Vertical diode and method for manufacturing vertical diode

Abstract

Provided is a vertical diode in which a first electrode, an organic semiconductor layer, and a second electrode are laminated adjacently in the stated order, wherein low-molecular hydrophobic ions are attached to the surface of the first electrode adjacent to the organic semiconductor layer.

Description

Vertical diode and method for manufacturing the same

[0001] The present disclosure relates to vertical diodes and methods for manufacturing vertical diodes.

[0002] In organic semiconductor devices having a diode structure, attempts have been made to adjust the work function of the electrodes or to dope the organic semiconductor disposed near the electrodes in order to improve various device performances such as rectification characteristics and power conversion efficiency.

[0003] For example, Non-Patent Document 1 discloses a method for adjusting the work function of an electrode by coating the electrode with a polymer material such as polyethyleneimine, and Non-Patent Document 2 discloses a method for adjusting the work function of an electrode by forming a thin film on the electrode using a material such as a polymer electrolyte and a tertiary aliphatic amine.

[0004] Advanced Materials, 2020, Vol.32, Issue33, 2002329Advanced Materials Interfaces, 2014, Vol.1, Issue8, 1400189

[0005] A diode is a device that has rectification characteristics in which current flows only in the forward direction and is difficult to flow in the reverse direction, but diodes obtained by modifying the electrode surface by the methods described in Non-Patent Documents 1 and 2 may have insufficient rectification characteristics, and improvements are desired. An object of the present disclosure is to provide a vertical diode with excellent rectification characteristics.

[0006] In order to solve the above problems, the present inventors have conducted extensive research. As a result, they have found that a vertical diode with excellent rectification characteristics can be obtained by using an electrode whose surface is modified with hydrophobic closed-shell ions. They have also found that a vertical diode with excellent rectification characteristics can be obtained by injecting carriers and dopant ions into an organic semiconductor in the vicinity of the electrode. That is, the gist of the present disclosure is as follows.

[0007] [1] A vertical diode having a first electrode, an organic semiconductor layer, and a second electrode stacked adjacent to each other in this order, wherein a low-molecular-weight hydrophobic ion is attached to a surface of the first electrode adjacent to the organic semiconductor layer. [2] The vertical diode according to [1], wherein the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic closed-shell ion. [3] The vertical diode according to [1] or [2], wherein the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic cation, wherein the low-molecular-weight hydrophobic cation is one or more selected from the group consisting of cations represented by formulas (1A) to (1F). wherein M1 is rhodium or iridium; M2 is ruthenium; M3 is cobalt; R １ ~R ６ are each independently a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent.) [4] The vertical diode according to [1] or [2], wherein the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic anion, and the low-molecular-weight hydrophobic anion is one or more selected from the group consisting of anions represented by formulas (3F) to (3G): (In the formula, R １４ are each independently a hydrogen atom, a halogen atom, or an optionally substituted fluorinated alkyl group; R １５ are each independently a perfluoroalkyl group, and two R １５may be linked to each other to form a ring.) [5] The vertical diode according to any one of [1] to [4], wherein the small-molecular-weight hydrophobic ions are attached to 10 to 50 area % of the surface of the first electrode adjacent to the organic semiconductor layer. [6] The vertical diode according to any one of [1] to [5], wherein the small-molecular-weight hydrophobic ions form an ion layer on the surface of the first electrode adjacent to the organic semiconductor layer, and the thickness of the ion layer is 2 nm or less or 3 molecular layers or less. [7] The vertical diode according to any one of [1] to [6], wherein, among the small-molecular-weight hydrophobic ions attached to the surface of the first electrode adjacent to the organic semiconductor layer, a proportion of the small-molecular-weight hydrophobic ions forming salts with counter ions is 25 mol % or less, and the counter ions are counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, and ions of a metal contained in the first electrode. [8] The vertical diode according to any one of [1] to [7], wherein the first electrode is a copper electrode. [9] The vertical diode according to any one of [1] to [3] and [5] to [8], wherein the small-molecular-weight hydrophobic ion is a small-molecular-weight hydrophobic cation, the organic semiconductor layer has a doped layer and an undoped layer, the doped layer is a layer adjacent to the second electrode, and contains holes and dopant anions.

[10] The vertical diode according to any one of [1] to [2] and [4] to [8], wherein the small-molecular-weight hydrophobic ion is a small-molecular-weight hydrophobic anion, the organic semiconductor layer has a doped layer and an undoped layer, the doped layer is a layer adjacent to the second electrode, and contains electrons and dopant cations.

[11] The vertical diode according to any one of [1] to

[10] , wherein the thickness of the organic semiconductor layer is 15 nm or more and 50 nm or less.

[12] The vertical diode according to any one of [1] to

[11] , wherein the conversion efficiency from AC power at a frequency of 10 MHz to DC power is more than 5%.

[13] The vertical diode according to any one of [1] to

[12] , having a conversion efficiency from AC power at a frequency of 1 GHz to DC power of more than 5%.

[14] A method for manufacturing a vertical diode having a first electrode, an organic semiconductor layer, and a second electrode stacked adjacent to each other in this order, the method comprising: an electrode modification step of contacting a surface of the first electrode with a surface modification liquid to obtain a surface-modified first electrode; and a lamination step of laminating the first electrode and the organic semiconductor layer so that the surface of the first electrode modified in the electrode modification step comes into contact with the organic semiconductor layer, wherein the surface modification liquid is any of the following surface modification liquids (S1) to (S4): (S1) A surface modification liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation; (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion; (S3) A surface modification liquid containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation; or (S4) A surface modification liquid containing a second oxidizing agent that oxidizes the first electrode and a low-molecular-weight hydrophobic closed-shell anion.

[15] The method for manufacturing a vertical diode according to

[14] , wherein the surface modifying liquid (S1) further contains a low-molecular-weight hydrophobic cation different from the low-molecular-weight hydrophobic cation generated from the first reducing agent.

[16] The method for manufacturing a vertical diode according to

[14] , wherein the surface modifying liquid (S2) further contains a low-molecular-weight hydrophobic anion different from the low-molecular-weight hydrophobic anion generated from the first oxidizing agent.

[17] The method for manufacturing a vertical diode according to any one of

[14] to

[16] , wherein the surface modifying liquid is the surface modifying liquid (S1) or the surface modifying liquid (S2).

[18] The method for manufacturing a vertical diode according to

[14] , wherein the surface modifying liquid is the surface modifying liquid (S3) or the surface modifying liquid (S4).

[19] The method for manufacturing a vertical diode according to any one of

[14] to

[18] , wherein a solvent of the surface modifying liquid is water, and the electrode modification step is performed under air atmosphere.

[20] The method for manufacturing a vertical diode according to any one of

[14] to

[19] , wherein the organic semiconductor layer is an organic semiconductor layer having a doped layer and an undoped layer, and the doped layer is a layer adjacent to the second electrode, and further comprising: a doping step of forming the doped layer by contacting a surface of an organic semiconductor layer precursor with an aqueous solution containing one or more selected from the group consisting of a third oxidizing agent and a third reducing agent and a salt of a dopant ion; and a lamination step of laminating the organic semiconductor layer and the second electrode so that the doped layer and the second electrode are in contact with each other.

[21] The method for manufacturing a vertical diode according to

[20] , wherein the third reducing agent is one or more selected from the group consisting of a hydroquinone compound having a hydroquinone skeleton and a reduced coenzyme, and the third oxidizing agent is a quinone compound having a quinone skeleton.

[22] A surface modifying liquid for modifying the surface of an electrode and changing the work function of the electrode, the surface modifying liquid being any of the following surface modifying liquids (S1) to (S4): (S1) A surface modifying liquid containing a first reducing agent that reduces the electrode and generates a low-molecular-weight hydrophobic cation; (S2) A surface modifying liquid containing a first oxidizing agent that oxidizes the electrode and generates a low-molecular-weight hydrophobic anion; (S3) A surface modifying liquid containing a second reducing agent that reduces the electrode and a low-molecular-weight hydrophobic closed-shell cation; (S4) A surface modifying liquid containing a second oxidizing agent that oxidizes the electrode and a low-molecular-weight hydrophobic closed-shell anion.

[23] The surface modifying liquid according to

[22] , wherein the surface modifying liquid (S1) further contains a low-molecular-weight hydrophobic cation different from the low-molecular-weight hydrophobic cation generated from the first reducing agent.

[24] The surface modifying liquid according to

[22] , wherein the surface modifying liquid (S2) further contains a low-molecular-weight hydrophobic anion different from the low-molecular-weight hydrophobic anion generated from the first oxidizing agent.

[25] The surface modifying liquid according to any one of

[22] to

[24] , wherein the surface modifying liquid is the surface modifying liquid (S1) or the surface modifying liquid (S2).

[26] The surface modifying liquid according to

[22] , wherein the surface modifying liquid is the surface modifying liquid (S3) or the surface modifying liquid (S4).

[27] The surface modifying liquid according to any one of

[22] to

[26] , wherein the solvent of the surface modifying liquid is water.

[28] A vertical diode comprising a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode stacked adjacent to each other in this order, with the doped layer adjacent to the first electrode or the second electrode, wherein the doped layer contains carriers and dopant ions, and the dopant ions are hydrophobic closed-shell ions.

[29] The vertical diode according to

[28] , wherein the doped layer is a layer adjacent to the second electrode, the carriers are holes, the dopant ions are hydrophobic closed-shell anions, and low-molecular-weight hydrophobic closed-shell cations are attached to a surface of the first electrode adjacent to the organic semiconductor layer.

[30] The vertical diode according to

[28] , wherein the doped layer is a layer adjacent to the second electrode, the carriers are electrons, the dopant ions are hydrophobic closed-shell cations, and low-molecular-weight hydrophobic closed-shell anions are attached to a surface of the first electrode adjacent to the organic semiconductor layer.

[31] The vertical diode according to any one of

[28] to

[30] , wherein the ratio of the dopant ions forming salts with counter ions among the dopant ions contained in the doped layer is 25 mol % or less, and the counter ions are ions derived from an organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of a metal contained in the first electrode, and ions of a metal contained in the second electrode.

[32] The vertical diode according to any one of

[28] to

[31] , wherein the organic semiconductor constituting the doped layer is the same compound as the organic semiconductor constituting the undoped layer.

[33] The vertical diode according to any one of

[28] to

[32] , wherein the thickness of the organic semiconductor layer is 15 nm or more and 50 nm or less.

[34] A method for manufacturing a vertical diode including a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode, which are stacked adjacent to each other in this order, and the doped layer is stacked adjacent to the first electrode or the second electrode, the method comprising: a doping step of forming the doped layer by bringing an aqueous solution containing a fourth oxidizing agent or a fourth reducing agent and a salt of a dopant ion into contact with a surface of an organic semiconductor layer precursor, wherein the dopant ion is a hydrophobic closed-shell ion.

[35] The method for manufacturing a vertical diode according to

[34] , wherein the fourth reducing agent is one or more selected from the group consisting of a hydroquinone compound having a hydroquinone skeleton and a reduced coenzyme, and the fourth oxidizing agent is a quinone compound having a quinone skeleton.

[36] The method for manufacturing a vertical diode according to

[34] or

[35] , wherein the doped layer is a layer adjacent to the second electrode, and the method further comprises an electrode modification step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with a surface modification liquid, and the surface modification liquid is any of the following surface modification liquids (S1) to (S4). (S1) A surface modification liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation. (S4) A surface modification liquid containing a second oxidizing agent that oxidizes the first electrode and a low-molecular-weight hydrophobic closed-shell anion.

[37] The method for manufacturing a vertical diode according to

[36] , wherein the surface modification liquid is the surface modification liquid (S1) or the surface modification liquid (S2).

[38] The method for manufacturing a vertical diode according to

[36] , wherein the surface modification liquid is the surface modification liquid (S3) or the surface modification liquid (S4).

[39] The method for manufacturing a vertical diode according to any one of

[36] to

[38] , wherein a solvent of the surface modification liquid is water, and the electrode modification step is performed under air atmosphere.

[0008] According to the present disclosure, it is possible to provide an effect of providing a vertical diode with excellent rectification characteristics. The problems and effects of the present disclosure are not limited to those specifically described above, but also include those that will become apparent to those skilled in the art from the entire specification.

[0009] 1 is an energy diagram of PBTTT and BQ / HQ. It is a diagram illustrating a doping process according to an embodiment of the present disclosure. It is a graph plotting the change in the redox potential of BQ / HQ with pH in an equilibrium diagram of water potential-pH. It is a cross-sectional schematic diagram showing the structure of a vertical diode according to a second embodiment. It is a cross-sectional schematic diagram showing the structure of a vertical diode according to a fourth embodiment. It is a schematic diagram of a circuit used to evaluate 10% rectification at 1 GHz of the vertical diode prepared in Example 13. It is a diagram showing the evaluation results of 10% rectification at 1 GHz of the vertical diode prepared in Example 13. It is a diagram showing the evaluation results of the AC power to DC power conversion efficiency of the vertical diode prepared in Example 6. It is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 1. It is a diagram showing the UPS measurement results of the surface-modified Cu electrode prepared in Example 2. It is a diagram showing the UPS measurement results of the unmodified Cu electrode prepared in Comparative Example 1. It is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 3. FIG. 1 shows the current-voltage characteristics of the vertical diode prepared in Example 4. FIG. 2 shows the current-voltage characteristics of the vertical diode prepared in Example 5. FIG. 3 shows the current-voltage characteristics of the vertical diode prepared in Example 6. FIG. 4 shows the current-voltage characteristics of the vertical diode prepared in Example 7. FIG. 5 shows the current-voltage characteristics of the vertical diode prepared in Comparative Example 2. FIG. 6 shows the current-voltage characteristics of the vertical diode prepared in Comparative Example 3. FIG. 7 shows the results of PYS measurement of the surface-modified ITO electrode prepared in Example 8. FIG. 8 shows the results of PYS measurement of the unmodified ITO electrode prepared in Comparative Example 3. FIG. 9 shows the results of PYS measurement of the surface-modified ITO electrode prepared in Comparative Example 4. FIG. 10 shows the results of XPS elemental analysis of the unmodified ITO electrode prepared in Comparative Example 3. FIG. 11 shows the results of XPS elemental analysis of the surface-modified ITO electrode prepared in Example 9. FIG. 12 shows the results of XPS elemental analysis of the unmodified ITO electrode prepared in Comparative Example 5. FIG. 13 shows the current-voltage characteristics of the vertical diode prepared in Example 10. 1 is a diagram showing the current-voltage characteristics of a vertical diode fabricated in Comparative Example 6. FIG. 2 is a diagram showing the current-voltage characteristics of a vertical diode fabricated in Example 11. FIG. 3 is a diagram showing the current-voltage characteristics of a vertical diode fabricated in Example 12.13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 13. FIG. 14 is a diagram showing the evaluation results of the AC power to DC power conversion efficiency of the vertical diode fabricated in Example 13. FIG. 15 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 14.

[0010] The present disclosure will be described below with reference to specific embodiments. However, each configuration and combination thereof in each embodiment is merely an example, and addition, omission, substitution, and other modifications of the configuration are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited by the embodiments. Furthermore, each aspect disclosed in this specification can be combined with any other feature disclosed in this specification.

[0011] In this specification, the term "X to Y" indicating a range means "X or more and Y or less." Furthermore, when a numerical range expressed as "X to Y" or "X or more and Y or less" is described in stages (for example, in order of preference), the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, in this disclosure, a description such as "X such as x1, x2, and x3" lists x1, x2, and x3 as examples of X, and does not mean that X is limited to x1, x2, x3, and the like.

[0012] [1. Method for Manufacturing a Vertical Diode] A first embodiment of the present disclosure is a method for manufacturing a vertical diode in which a first electrode, an organic semiconductor layer, and a second electrode are stacked adjacent to each other in this order. The manufacturing method according to this embodiment includes an electrode modification step of contacting a surface of a first electrode with a surface modification liquid to obtain a surface-modified first electrode; and a lamination step of laminating the first electrode and the organic semiconductor layer so that the surface of the first electrode modified in the electrode modification step contacts the organic semiconductor layer. The surface modification liquid used in the electrode modification step is any one of surface modification liquids (S1) to (S4). (S1) A surface modification liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation. (S4) A surface modifying solution containing a second oxidizing agent for oxidizing the first electrode and a low-molecular-weight hydrophobic closed-shell anion.

[0013] In the present disclosure, "hydrophobic" means a property of having a low affinity for water and not dissolving or mixing in water or being difficult to do so.

[0014] In the present disclosure, "hydrophobic" ions (cations or anions) refer to ions containing one or more hydrophobic moieties. Preferred examples of hydrophobic moieties include aromatic hydrocarbon groups having 5 to 20 carbon atoms, such as cyclopentadienyl groups and phenyl groups; aromatic heterocyclic groups having 3 to 20 carbon atoms, such as imidazolyl groups; hydrocarbon groups having 8 to 20 carbon atoms, such as octyl groups; fluorinated aliphatic hydrocarbon groups having 1 to 20 carbon atoms, such as trifluoromethyl and pentafluoroethyl groups, preferably perfluoroaliphatic hydrocarbon groups; and fluorinated aromatic hydrocarbon groups having 6 to 20 carbon atoms, such as pentafluorophenyl groups and heptafluoronaphthyl groups, preferably perfluoroaromatic hydrocarbon groups. The number of hydrophobic moieties per molecule of the hydrophobic ion is preferably 1 to 10, more preferably 1 to 8, even more preferably 2 to 6, and particularly preferably 2 to 4. When the number of hydrophobic moieties is equal to or greater than the above lower limit, the ions become sufficiently bulky and exhibit hydrophobicity, thereby obtaining a surface-modified electrode that is highly stable against water and air. When the number of hydrophobic moieties is equal to or less than the above upper limit, a surface-modifying liquid containing hydrophobic ions at a sufficient concentration can be prepared.

[0015] It is desirable for the hydrophobic ion to have a charge that is widely delocalized within the hydrophobic ion. This is because the delocalization of the charge can suppress local interactions with water, improving the hydrophobicity of the hydrophobic ion. In order to delocalize the charge over a wide range of the hydrophobic ion, it is preferable to give the hydrophobic ion a conjugated structure, an electron-withdrawing group (when the hydrophobic ion is a hydrophobic anion), an electron-donating group (when the hydrophobic ion is a hydrophobic cation), or the like.

[0016] In the present disclosure, the term "low molecular weight" means that the molecule does not have a molecular weight distribution and has a molecular weight of 2,000 or less, preferably 1,000 or less, more preferably 800 or less, and even more preferably 500 or less. In contrast, molecules or ions that have a molecular weight distribution and have a molecular weight of 1,000 or more are distinguished from the latter by being called "macromolecules" or "polymers."

[0017] According to this embodiment, a vertical diode exhibiting excellent rectification characteristics can be obtained. Therefore, the manufacturing method according to this embodiment is useful as a method for manufacturing a rectifier diode. A rectifier diode has a higher current value in the forward direction than in the reverse direction, and the rectification ratio, which is the ratio, is two digits or more, preferably three digits or more. Furthermore, as will be described later, it is possible to greatly change the work function of the first electrode, thereby greatly improving the degree of freedom in selecting electrode materials. Furthermore, according to a preferred aspect of this embodiment, a vertical diode with excellent high-frequency response or a vertical diode exhibiting high current density even at a low voltage can be obtained. In this disclosure, "current density" refers to the forward current density. Furthermore, "high current density at a low voltage" refers to a forward current density of 1 Acm at a forward voltage of 2 V. －２ More than 10 Acm, preferably 10 Acm －２ More preferably, 100 Acm －２ The vertical diode obtained by the manufacturing method according to the present embodiment is considered to be applicable to various devices having a diode structure, such as solar cells and light-emitting diodes, and is also expected to be applied to electronic tags for wireless communication, which require high-frequency response.

[0018] [1-1. Electrode Modification Step] The electrode modification step is a step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with any one of the surface modifying solutions (S1) to (S4).

[0019] This step provides a surface-modified first electrode (hereinafter, sometimes referred to as a "surface-modified electrode"), in which low-molecular-weight hydrophobic ions are attached to the surface of the first electrode that is adjacent to the organic semiconductor layer when the vertical diode is fabricated.

[0020] In the electrode modification step, the work function of the first electrode can be significantly shifted by a simple solution process in which the surface of the first electrode is brought into contact with a surface modification solution. In addition, conventional techniques for changing the work function of an electrode by surface modification, such as polymer deposition, have the problem that the resulting electrode has low atmospheric stability, and when exposed to the atmosphere, the work function returns to approximately the same level as before the surface modification. However, the electrode modification step of this embodiment can provide a surface-modified electrode with high water resistance and atmospheric stability. Therefore, as shown in the examples described below, the work function, which has been shifted shallowly or deeply in the electrode modification step, is maintained even when the work function of the surface-modified electrode is measured after exposure to the atmosphere.

[0021] Here, the work function is the difference (positive value) between the Fermi level and the vacuum level. The Fermi level is the energy level at which the electron occupancy probability is 0.5. In a metal, the work function is equal to the ionization potential, which is the minimum energy required to extract one electron into a vacuum. The work function can be measured using an ultraviolet photoelectron spectroscopy device. However, when the measurement target is a metal, the work function is taken to be a value measured using a photoelectron yield spectroscopy device (for example, "AC-3" manufactured by Riken Keiki Co., Ltd.) for measuring the ionization potential.

[0022] [1-1-1. Surface modifying liquid] The surface modifying liquids (S1) to (S4) for modifying the surface of the first electrode are preferably solutions or dispersions, more preferably solutions. The components contained in the surface modifying liquids (S1) to (S4) are described below.

[0023] (Surface Modifying Liquid (S1)) The first reducing agent contained in the surface modifying liquid (S1) is a compound that reduces the first electrode and generates low-molecular-weight hydrophobic cations. When the surface modifying liquid (S1) is used as the surface modifying liquid, in this step, electrons are injected into the first electrode (i.e., the surface of the first electrode is reduced), thereby negatively charging the surface of the first electrode. Then, low-molecular-weight hydrophobic cations generated from the first reducing agent electrostatically attach to the negatively charged surface of the first electrode, thereby obtaining a surface-modified first electrode. At this time, the low-molecular-weight hydrophobic cations electrostatically attach to the first electrode to form a cation layer. The thickness of the cation layer is preferably three molecular layers or less, more preferably two molecular layers or less, and even more preferably a monolayer or less. Specifically, the thickness of the cation layer is preferably 2 nm or less, more preferably 1 nm or less. The thickness of the cation layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis. The first reducing agent that generates a low-molecular-weight hydrophobic cation is also a low-molecular-weight compound.

[0024] The surface modifying liquid (S1) preferably further contains low-molecular-weight hydrophobic cations (hereinafter, sometimes referred to as "other low-molecular-weight hydrophobic cations") different from the low-molecular-weight hydrophobic cations derived from the first reducing agent. When the surface modifying liquid (S1) further contains other low-molecular-weight hydrophobic cations, the other low-molecular-weight hydrophobic cations electrostatically attach to the first electrode, which has been negatively charged by reduction, or the low-molecular-weight hydrophobic cations derived from the first reducing agent that have electrostatically attached to the first electrode are replaced by the other low-molecular-weight hydrophobic cations. Therefore, a cation layer is formed on the surface of the first electrode by the low-molecular-weight hydrophobic cations derived from the first reducing agent and the other low-molecular-weight hydrophobic cations, or by the other low-molecular-weight hydrophobic cations. The molar ratio of the low-molecular-weight hydrophobic cations derived from the first reducing agent to the other low-molecular-weight hydrophobic cations in the cation layer can be adjusted by adjusting the concentration or degree of hydrophobicity of the other low-molecular-weight hydrophobic cations in the surface modifying liquid (S1).

[0025] Therefore, when the stability of the low molecular weight hydrophobic cation generated from the first reducing agent is insufficient, or when the first reducing agent is expensive, etc., by adding another low molecular weight hydrophobic cation to the surface modifying liquid (S1), it becomes possible to produce a surface-modified electrode that is more stable to air and water at lower cost.

[0026] Hereinafter, the low molecular weight hydrophobic cations derived from the first reducing agent and other low molecular weight hydrophobic cations may be collectively referred to as "low molecular weight hydrophobic cations" or "low molecular weight hydrophobic ions."

[0027] When the surface of the first electrode is modified as described above, a large dipole is formed at the interface between the surface of the first electrode and the low-molecular-weight hydrophobic cation, resulting in a work function of the first electrode that is shallower (smaller) than before modification. The shift in the work function of the first electrode due to the electrode modification step in this embodiment is very large. For example, as shown in the examples described below, the work function of a gold electrode shifts from approximately 5.0 eV to approximately 3.7 eV due to surface modification.

[0028] By reducing the work function of the first electrode, the electron injection from the first electrode to the organic semiconductor layer is greatly improved. This allows electrons from the first electrode to easily enter the LUMO of the organic semiconductor, facilitating electron transfer from the first electrode through the organic semiconductor layer to the second electrode. Meanwhile, the electron injection from the second electrode to the organic semiconductor layer remains almost unchanged, making electron transfer from the second electrode to the first electrode more difficult than electron transfer from the first electrode to the second electrode. In other words, surface modification of the first electrode facilitates current flow from the second electrode to the first electrode, while the ease of current flow from the first electrode to the second electrode remains almost unchanged. This improves the rectification characteristics of the vertical diode, ultimately achieving stable operation of the vertical diode. It also makes it possible to increase the current density of the vertical diode at low voltages.

[0029] As described above, when the first electrode is modified with the surface modifying liquid (S1) containing the first reducing agent, a vertical diode with excellent rectification characteristics can be obtained by using an electron-transporting organic semiconductor layer, i.e., an n-type organic semiconductor layer, as the organic semiconductor layer and using the first electrode as an electron injection electrode (cathode (negative electrode)). Furthermore, a vertical diode exhibiting high current density even at low voltage can be obtained. In this case, the entire organic semiconductor layer does not need to be an n-type organic semiconductor layer; for example, when the organic semiconductor layer has a multilayer structure, the above-described effects can be similarly obtained as long as only the layer adjacent to the first electrode is an n-type organic semiconductor layer.

[0030] Here, a method for adjusting the work function of an electrode by depositing a polymer or salt on the electrode is known as a conventional technique. However, in the polymer deposition method, a polymer layer thicker than a monolayer is formed between the electrode and the organic semiconductor layer, resulting in a significant decrease in electron injection from the electrode to the organic semiconductor layer. In the salt deposition method, a salt of a cation species and a counter anion such as a halide ion is used as the salt to be deposited on the electrode. This salt not only reduces electron injection from the electrode to the organic semiconductor layer, but also causes the problem that halide ions and the like diffuse into the organic semiconductor layer, thereby reducing the device's lifespan. Furthermore, even when these materials are thinly deposited, both polymers and salts contain moieties other than those responsible for work function control, and therefore, excessive activity that hinders electron injection is unavoidable.

[0031] Another prior art technique involves controlling the work function by covalently bonding a self-assembled monolayer to a metal and using the dipole of the monolayer. This technique requires the use of molecular materials that react appropriately with the metal species on a clean metal surface. Using clean surfaces in actual semiconductor device manufacturing processes is often difficult given other processes, such as lithography. Furthermore, limitations are placed on the metal species. Furthermore, the bonds formed by the self-assembled monolayer material are often not strong, and thermal detachment can occur. On the other hand, this technique uses a redox reaction, making it possible to perform processing in principle without depending on the surface cleanliness or the type of metal or conductive material. Therefore, the manufacturing method according to this embodiment has fundamental advantages in semiconductor device manufacturing.

[0032] In this embodiment, low-molecular-weight hydrophobic cations are attached (adsorbed) to the surface of the negatively charged first electrode by a reduction reaction to form a thin cation layer, which effectively prevents the formation of an excess layer that inhibits electron transfer between the first electrode and the organic semiconductor layer or the formation of salts, thereby achieving not only excellent electron transfer between the first electrode and the organic semiconductor layer and the rectifying characteristics of the vertical diode, but also a longer lifespan and improved current density at low voltages of the vertical diode.

[0033] The first reducing agent is not particularly limited as long as it can generate electrons and low-molecular-weight hydrophobic cations and reduce the first electrode.

[0034] The low-molecular-weight hydrophobic cation generated from the first reducing agent is preferably a low-molecular-weight hydrophobic cation that is highly hydrophobic and stable to air and water, and more preferably a low-molecular-weight hydrophobic closed-shell cation, because low-molecular-weight hydrophobic closed-shell cations are highly stable in solvents, particularly in water.

[0035] Preferred examples of the low-molecular-weight hydrophobic cation generated from the first reducing agent include low-molecular-weight hydrophobic closed-shell cations represented by formulas (1A) to (1C). The low-molecular-weight hydrophobic cation generated from the first reducing agent is preferably one or more selected from the cations represented by formulas (1A) to (1B), and more preferably one or more selected from the cation represented by formula (1B) in terms of higher stability to air and water.

[0036]

[0037] In the formula, M1 is rhodium or iridium, preferably rhodium.

[0038] In the formula, M2 is ruthenium.

[0039] wherein M3 is cobalt.

[0040] In the formula, R １ ~R ３ are each independently a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent.

[0041] R １ is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group. ２ is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group. ３ is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group.

[0042] R １ ~R ３Examples of the substituent that the alkyl group and aryl group represented by the formula (I) may have include, but are not limited to, a deuterium atom; a hydroxy group; a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom; an alkyl group having from 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, or an isopropyl group; a cycloalkyl group such as a cyclopropyl group or a cyclobutyl group; an aryl group having from 6 to 12 carbon atoms such as a phenyl group, a 1-naphthyl group, or a 2-naphthyl group; and an aralkyl group such as a benzyl group or a 2-phenylethyl group.

[0043] R １ ~R ３ The number of carbon atoms in the alkyl group which may have a substituent, represented by the following formula (I), is not particularly limited, but is preferably 1 or more and 20 or less, more preferably 1 or more and 12 or less, even more preferably 2 or more and 8 or less, and particularly preferably 2 or more and 6 or less.

[0044] R １ ~R ３ Specific examples of the alkyl group represented by the formula (I) which may have a substituent include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, a trifluoromethyl group, a pentafluoroethyl group, a hydroxymethyl group, and a 2-hydroxyethyl group, and a methyl group is preferred.

[0045] R １ ~R ３ The number of carbon atoms of the aryl group represented by the following formula (1) which may have a substituent is not particularly limited, but is preferably 6 or more and 20 or less, and more preferably 6 or more and 14 or less.

[0046] R １ ~R ３ Specific examples of the aryl group represented by the formula (I) which may have a substituent include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 9-phenanthrenyl group, a 9-fluorenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a mesityl group, a pentafluorophenyl group, and a p-trifluoromethyl group, and are preferably a phenyl group or a mesityl group.

[0047] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1A) include the following cations.

[0048]

[0049] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1B) include the following cations.

[0050]

[0051] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1C) include the following cations.

[0052]

[0053] Examples of first reducing agents that generate these low-molecular-weight hydrophobic cations include compounds represented by formulas (2A) to (2C). The compounds represented by formulas (2A) to (2C) are first reducing agents that generate low-molecular-weight hydrophobic closed-shell cations represented by formulas (1A) to (1C), respectively. Therefore, among these, the first reducing agent is preferably one or more selected from the compounds represented by formulas (2A) to (2B), and more preferably one or more selected from the compounds represented by formula (2B) in that it can generate low-molecular-weight hydrophobic closed-shell cations that are more stable to air and water.

[0054]

[0055] M1 and R in formula (2A) １ respectively represent M1 and R in formula (1A). １ The preferred embodiments of M and R in formula (2B) are also the same. ２ respectively represent M2 and R in formula (1B). ２ The preferred embodiments of M3 and R in formula (2C) are also the same. ３ respectively represent M3 and R in formula (1C). ３ The same applies to the preferred embodiments thereof.

[0056] Specific preferred examples of the compound represented by formula (2A) include the following compounds:

[0057]

[0058] Specific preferred examples of the compound represented by formula (2B) include the following compounds:

[0059]

[0060] Preferred examples of the compound represented by formula (2C) include cobaltocene and decamethylcobaltocene.

[0061] The first reducing agent may be used alone or in any combination of two or more kinds in any ratio. Accordingly, the low-molecular-weight hydrophobic cation attached to the surface of the first electrode may also be used alone or in any combination of two or more kinds.

[0062] The other low-molecular-weight hydrophobic cations contained in the surface-modifying liquid (S1) are synonymous with the low-molecular-weight hydrophobic cations derived from the first reducing agent, and preferred embodiments thereof are also the same. The low-molecular-weight hydrophobic cations may be used alone, or two or more may be used in any ratio and combination. However, the other low-molecular-weight hydrophobic cations contained in one surface-modifying liquid (S1) are cations different from the low-molecular-weight hydrophobic cations derived from the first reducing agent.

[0063] Counter anions of other low-molecular-weight hydrophobic cations contained in the surface modifying liquid (S1) are not particularly limited, and examples thereof include hydroxide ions, halide ions such as chloride ions, bromide ions, and iodide ions, carbonate ions, sulfate ions, and phosphate ions. Of these, hydroxide ions are preferred as counter anions, since they can suppress the deposition of halide salts that inhibit electron injection from the first electrode to the organic semiconductor layer.

[0064] The total concentration of the first reducing agent in the surface modifying liquid (S1) is not particularly limited and may be appropriately selected depending on the type of the first reducing agent, the coverage of the low-molecular-weight hydrophobic ion described below, the shift width of the work function, etc. For example, the total concentration of the first reducing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.

[0065] When the surface modifying liquid (S1) contains other low-molecular-weight hydrophobic cations, the total concentration of the other low-molecular-weight hydrophobic cations in the surface modifying liquid (S1) is not particularly limited and may be appropriately selected depending on the types of the other low-molecular-weight hydrophobic cations, the low-molecular-weight hydrophobic ion coverage rate (described later), the shift width of the work function, the proportion of the other low-molecular-weight hydrophobic cations in all the low-molecular-weight hydrophobic cations modifying the first electrode, etc. For example, the total concentration of the low-molecular-weight hydrophobic cations is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.

[0066] (Surface Modifying Liquid (S2)) The first oxidizing agent contained in the surface modifying liquid (S2) is a compound that oxidizes the first electrode and generates low-molecular-weight hydrophobic anions. When the surface modifying liquid (S2) is used as the surface modifying liquid, in this step, holes are injected into the first electrode (i.e., the surface of the first electrode is oxidized), thereby positively charging the surface of the first electrode. Then, low-molecular-weight hydrophobic anions generated from the first oxidizing agent electrostatically attach to the positively charged surface of the first electrode, thereby obtaining a surface-modified first electrode. At this time, the low-molecular-weight hydrophobic anions electrostatically attach to the first electrode to form an anion layer. The thickness of the anion layer is preferably three molecular layers or less, more preferably two molecular layers or less, and even more preferably a monolayer or less. Specifically, the thickness of the anion layer is preferably 2 nm or less, more preferably 1 nm or less. The thickness of the anion layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis. The first oxidizing agent that generates a low-molecular-weight hydrophobic anion is also a low-molecular-weight compound.

[0067] Preferably, the surface modifying liquid (S2) further contains low-molecular-weight hydrophobic anions (hereinafter, sometimes referred to as "other low-molecular-weight hydrophobic anions") different from the low-molecular-weight hydrophobic anions derived from the first oxidizing agent. When the surface modifying liquid (S2) further contains the other low-molecular-weight hydrophobic anions, the other low-molecular-weight hydrophobic anions electrostatically attach to the first electrode, which has been positively charged by oxidation, or the low-molecular-weight hydrophobic anions derived from the first oxidizing agent and electrostatically attached to the first electrode are replaced by the other low-molecular-weight hydrophobic anions. Therefore, an anion layer is formed on the surface of the first electrode by the low-molecular-weight hydrophobic anions derived from the first oxidizing agent and the other low-molecular-weight hydrophobic anions, or by the other low-molecular-weight hydrophobic anions. The molar ratio of the low-molecular-weight hydrophobic anions derived from the first oxidizing agent to the other low-molecular-weight hydrophobic anions in the anion layer can be controlled by adjusting the concentration or degree of hydrophobicity of the low-molecular-weight hydrophobic anions in the surface modifying liquid (S2).

[0068] Therefore, when the stability of the low-molecular-weight hydrophobic anion generated from the first oxidizing agent is insufficient or when the first oxidizing agent is expensive, for example, by adding another low-molecular-weight hydrophobic anion to the surface modifying liquid (S2), it becomes possible to produce a surface-modified electrode that is more stable to air and water at lower cost.

[0069] Hereinafter, the low-molecular-weight hydrophobic anions derived from the first oxidizing agent and other low-molecular-weight hydrophobic anions may be collectively referred to as "low-molecular-weight hydrophobic anions" or "low-molecular-weight hydrophobic ions."

[0070] When the surface of the first electrode is modified as described above, a large dipole is formed at the interface between the surface of the first electrode and the low-molecular-weight hydrophobic anion, and as a result, the work function of the first electrode becomes deeper (larger) than before modification. The electrode modification step in this embodiment can significantly shift the work function of the first electrode.

[0071] Increasing the work function of the first electrode significantly improves hole injection from the first electrode to the organic semiconductor layer. This allows holes to be easily injected from the first electrode into the HOMO of the organic semiconductor, facilitating their migration from the first electrode through the organic semiconductor layer to the second electrode. Meanwhile, hole injection from the second electrode to the organic semiconductor layer remains largely unchanged, making hole migration from the second electrode to the first electrode more difficult than hole migration from the first electrode to the second electrode. In other words, surface modification of the first electrode facilitates current flow from the first electrode to the second electrode, while barely changing the ease of current flow from the second electrode to the first electrode. This improves the rectification characteristics of the vertical diode, ultimately achieving stable operation of the vertical diode. It also enables an increase in the current density of the vertical diode at low voltages.

[0072] As described above, when the first electrode is modified with the surface modifying liquid (S2) containing the first oxidizing agent, a vertical diode with excellent rectification characteristics can be obtained by using a hole-transporting organic semiconductor layer, i.e., a p-type organic semiconductor layer, and using the first electrode as a hole-injection electrode (anode (positive electrode)). Furthermore, a vertical diode exhibiting high current density even at low voltage can be obtained. In this case, the entire organic semiconductor layer does not need to be a p-type organic semiconductor layer; for example, when the organic semiconductor layer has a multilayer structure, the above-described effects can be similarly obtained as long as only the layer adjacent to the first electrode is a p-type organic semiconductor layer.

[0073] Furthermore, when the surface modifying liquid (S2) is used to modify the first electrode, problems such as the formation of an excess layer between the first electrode and the organic semiconductor layer that inhibits hole injection and the generation of salt are effectively suppressed for the same reasons as when the surface modifying liquid (S1) is used, thereby improving the hole injection from the first electrode to the organic semiconductor layer, and also achieving improvements in the rectification characteristics of the vertical diode, a longer life for the vertical diode, and an improvement in current density at low voltage.

[0074] The first oxidizing agent is not particularly limited as long as it can generate holes and low-molecular-weight hydrophobic anions and oxidize the first electrode.

[0075] The low-molecular-weight hydrophobic anion generated from the first oxidizing agent is preferably a low-molecular-weight hydrophobic anion that is highly hydrophobic and stable to air and water, more preferably a low-molecular-weight hydrophobic closed-shell anion or a low-molecular-weight hydrophobic radical anion, and even more preferably a low-molecular-weight hydrophobic closed-shell anion, because low-molecular-weight hydrophobic closed-shell anions are highly stable in solvents, particularly in water.

[0076] Examples of low molecular weight hydrophobic closed shell anions generated from the first oxidant include FeCl ４ － and anions represented by formulae (3A) to (3C).

[0077]

[0078] In the formula, R １１ are each independently a trifluoromethyl group (CF ３ ), a methyloxycarbonyl group (COOMe), or a trifluoromethyloxycarbonyl group (COOCF ３ )

[0079] In the formula, R １２ are each independently a hydrogen atom, a halogen atom, or an alkyl group which may have a substituent, preferably a hydrogen atom or a halogen atom, more preferably a halogen atom.

[0080] R １２ Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is preferred.

[0081] R １２ The alkyl group which may have a substituent represented by R １ ~R ３ The meaning of the alkyl group is the same as that of the alkyl group which may have a substituent represented by the following formula: and preferred embodiments thereof are also the same.

[0082] In the formula, R １３ are each independently a cyano group (CN) or a methyloxycarbonyl group (COOMe).

[0083] Examples of the first oxidizing agent that generates a low-molecular-weight hydrophobic closed-shell anion include iron(III) chloride and compounds represented by formulas (4A) to (4C). Iron(III) chloride is FeCl ４ － The compounds represented by formulas (4A) to (4C) are first oxidizing agents that produce low-molecular-weight hydrophobic closed-shell cations represented by formulas (3A) to (3C), respectively.

[0084]

[0085] R in formula (4A) １１ is R in formula (3A). １１ The preferred embodiments thereof are also the same. １２ is R in formula (3B). １２ The preferred embodiments thereof are also the same. １３ is R in formula (3C) １３ The same applies to the preferred embodiments thereof.

[0086] Examples of the low-molecular-weight hydrophobic radical anion generated from the first oxidizing agent include radical anions represented by formulas (3D) to (3E). Among these, the low-molecular-weight hydrophobic radical anion generated from the first oxidizing agent is preferably one or more types selected from the radical anion represented by formula (3D).

[0087]

[0088] In the formula, R １４ and R １５ are each independently a hydrogen atom, a halogen atom, or an alkyl group which may have a substituent, preferably a hydrogen atom or a halogen atom, more preferably a halogen atom.

[0089] R １４ and R １５ Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is preferred.

[0090] R １４ and R １５The alkyl group which may have a substituent represented by R １ ~R ３ The meaning of the alkyl group is the same as that of the alkyl group which may have a substituent represented by the following formula: and preferred embodiments thereof are also the same.

[0091] Specific examples of the low-molecular-weight hydrophobic radical anion represented by formula (3D) include the following anions.

[0092]

[0093] Specific examples of the low-molecular-weight hydrophobic radical anion represented by formula (3E) include the following anions.

[0094]

[0095] Examples of first oxidizing agents that generate low-molecular-weight hydrophobic radical anions include compounds represented by formulas (4D) to (4E). The compounds represented by formulas (4D) to (4E) are first oxidizing agents that generate low-molecular-weight hydrophobic radical cations represented by formulas (3D) to (3E), respectively. Therefore, among these, it is preferable that the first oxidizing agent is one or more compounds selected from the compounds represented by formula (4D).

[0096]

[0097] R in formula (4D) １４ is R in formula (3D) １４ The preferred embodiments thereof are also the same. １５ is R in formula (3E). １５ The same applies to the preferred embodiments thereof.

[0098] Specific preferred examples of the compound represented by formula (4D) include the following compounds:

[0099]

[0100] Specific preferred examples of the compound represented by formula (4E) include the following compounds:

[0101]

[0102] The first oxidizing agent may be used alone or in any combination of two or more kinds in any ratio. Accordingly, the low-molecular-weight hydrophobic anion attached to the surface of the first electrode may also be used alone or in any combination of two or more kinds.

[0103] The other low-molecular-weight hydrophobic anion contained in the surface-modifying liquid (S2) has the same meaning as the low-molecular-weight hydrophobic anion derived from the first oxidizing agent, and the preferred embodiments thereof are also the same. The low-molecular-weight hydrophobic anion may be used alone, or two or more types may be used in any ratio and combination. However, the other low-molecular-weight hydrophobic anion contained in one surface-modifying liquid (S2) is an anion different from the low-molecular-weight hydrophobic anion derived from the first reducing agent.

[0104] Counter cations of other low-molecular-weight hydrophobic anions contained in the surface modifying liquid (S2) are not particularly limited, and examples thereof include protons and metal ions such as lithium ions, sodium ions, and potassium ions. Of these, protons are preferred as the counter cations, since they can suppress the deposition of metal salts that inhibit hole injection from the first electrode to the organic semiconductor layer.

[0105] The total concentration of the first oxidizing agent in the surface modifying liquid (S2) is not particularly limited and may be appropriately selected depending on the type of the first oxidizing agent, the coverage of the low-molecular-weight hydrophobic ions described below, the shift width of the work function, etc. For example, the total concentration of the first oxidizing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.

[0106] When the surface modifying liquid (S2) contains other low-molecular-weight hydrophobic anions, the total concentration of the other low-molecular-weight hydrophobic anions in the surface modifying liquid (S2) is not particularly limited and may be appropriately selected depending on the type of the other low-molecular-weight hydrophobic anions, the low-molecular-weight hydrophobic ion coverage rate (described later), the shift width of the work function, the proportion of the other low-molecular-weight hydrophobic anions in all the low-molecular-weight hydrophobic anions modifying the first electrode, etc. For example, the total concentration of the low-molecular-weight hydrophobic anions is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.

[0107] (Surface modifying liquid (S3)) The second reducing agent contained in the surface modifying liquid (S3) is a compound that reduces the first electrode and does not generate low-molecular-weight hydrophobic cations. Furthermore, the second reducing agent is preferably a compound that does not generate any cationic species other than low-molecular-weight hydrophobic cations during the reduction of the first electrode. This is because the second reducing agent does not generate any cationic species, allowing the low-molecular-weight hydrophobic closed-shell cations contained in the surface modifying liquid (S3) to be selectively attached to the surface of the first electrode.

[0108] The second reducing agent can be the same as the third reducing agent described later, and compounds preferred as the third reducing agent are also preferred as the second reducing agent. That is, examples of the second reducing agent include hydroquinone compounds having a hydroquinone skeleton, which will be described later as the third reducing agent; dihydroxyfuranone compounds having a dihydroxyfuranone skeleton; sugars having reducing properties; and reduced coenzymes; and the like. The second reducing agent is preferably one or more selected from the group consisting of hydroquinone compounds having a hydroquinone skeleton and reduced coenzymes, and more preferably a reduced coenzyme.

[0109] It is particularly preferable that the low-molecular-weight hydrophobic closed-shell cation contained in the surface modifying liquid (S3) is one that is unlikely to undergo an oxidation-reduction reaction with water or an oxidation-reduction reaction with oxygen under temperature conditions of 15°C or higher and 35°C or lower (room temperature conditions) and in the air.

[0110] As such low-molecular-weight hydrophobic closed-shell cations, in addition to the low-molecular-weight hydrophobic closed-shell cations exemplified above as those generated from the first reducing agent, low-molecular-weight hydrophobic closed-shell cations represented by formulas (1D) to (1F) are preferably used.

[0111]

[0112] In the formula, R ４ ~R ６ are each independently a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent. ４ ~R ６ The alkyl group which may have a substituent and the aryl group which may have a substituent are represented by R １ ~R ３These groups have the same meanings as the alkyl group which may have a substituent and the aryl group which may have a substituent, as represented by the following formula:

[0113] R ４ is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, more preferably an aryl group which may have a substituent, and even more preferably an unsubstituted aryl group. ５ is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, more preferably an aryl group which may have a substituent, and even more preferably an unsubstituted aryl group. ６ is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, and more preferably an unsubstituted alkyl group or an aryl group which may have a substituent.

[0114] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1D) include the following cations.

[0115]

[0116] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1E) include the following cations.

[0117]

[0118] Specific examples of the low-molecular-weight hydrophobic closed-shell cation represented by formula (1F) include the following cations.

[0119]

[0120] The counter anion of the low-molecular-weight hydrophobic closed-shell cation contained in the surface modifying liquid (S3) is not particularly limited, and examples thereof include hydroxide ions, halide ions such as chloride ions, bromide ions, and iodide ions, carbonate ions, sulfate ions, and phosphate ions. Among these, hydroxide ions are preferred as the counter anion, since they can suppress the deposition of halide salts that inhibit electron injection from the first electrode to the organic semiconductor layer.

[0121] The total concentration of the second reducing agent in the surface modifying liquid (S3) is not particularly limited and may be appropriately selected depending on the type of the second reducing agent, the shift width of the work function, etc. For example, the total concentration of the second reducing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.

[0122] The total concentration of the low-molecular-weight hydrophobic closed-shell cations in the surface modifying liquid (S3) is not particularly limited and may be appropriately selected depending on the type of low-molecular-weight hydrophobic closed-shell cation, the low-molecular-weight hydrophobic ion coverage (described later), the shift width of the work function, etc. For example, the total concentration of the low-molecular-weight hydrophobic closed-shell cations is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.

[0123] When the counter anion of the low-molecular-weight hydrophobic closed-shell cation is a halide ion, the total concentration of the halide ions in the surface modifying liquid (S3) is preferably 100 ppm by mass or less, more preferably 10 ppm by mass or less, and even more preferably 1 ppm by mass or less. By keeping the halide ion concentration within this range, it is possible to suppress problems such as the deposition of unnecessary salts on the surface of the first electrode and the diffusion of halide ions into the organic semiconductor layer, which shortens the life of the vertical diode.

[0124] When the surface-modifying liquid (S3) is used as the surface-modifying liquid, electrons are injected into the first electrode (i.e., the surface of the first electrode is reduced), thereby negatively charging the surface of the first electrode. Then, low-molecular-weight hydrophobic closed-shell cations electrostatically attach to the negatively charged surface of the first electrode, resulting in a surface-modified first electrode. At this time, as in the case of using the surface-modifying liquid (S1), low-molecular-weight hydrophobic closed-shell cations electrostatically attach to the surface of the first electrode, forming a cation layer with a thickness of less than a monolayer. The thickness of the cation layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.

[0125] In this way, when the surface modifying liquid (S3) is used as the surface modifying liquid, the surface of the first electrode is modified in the same way as when the surface modifying liquid (S1) is used. Therefore, when the surface modifying liquid (S3) is used as the surface modifying liquid, the work function of the first electrode can be made shallow (small) as in the case of when the surface modifying liquid (S1) is used, and the rectifying characteristics of the vertical diode can be improved. In addition, it is also possible to increase the current density of the vertical diode at low voltages.

[0126] When the first electrode is modified with the surface modifying liquid (S3), a vertical diode with excellent rectification characteristics can be obtained by using an electron-transporting organic semiconductor layer, i.e., an n-type organic semiconductor layer, as the organic semiconductor layer and using the first electrode as an electron injection electrode (cathode (negative electrode)). Furthermore, a vertical diode exhibiting high current density even at low voltage can be obtained. In this case, the entire organic semiconductor layer does not need to be an n-type organic semiconductor layer; for example, when the organic semiconductor layer has a multilayer structure, the above-described effect can be similarly obtained as long as only the layer adjacent to the first electrode is an n-type organic semiconductor layer.

[0127] When the surface modifying liquid (S3) is used to modify the first electrode, problems such as the formation of an excess layer between the first electrode and the organic semiconductor layer that inhibits electron injection and the generation of salt are effectively suppressed for the same reasons as when the surface modifying liquid (S1) is used. As a result, the electron injection from the first electrode to the organic semiconductor layer can be improved, and the rectification characteristics of the vertical diode can be improved, the lifetime can be extended, and the current density at a low voltage can be improved.

[0128] (Surface modifying liquid (S4)) The second oxidizing agent contained in the surface modifying liquid (S4) is a compound that oxidizes the first electrode and does not generate low-molecular-weight hydrophobic anions. Furthermore, the second oxidizing agent is preferably a compound that does not generate any anion species other than low-molecular-weight hydrophobic anions during the oxidation of the first electrode. This is because the second oxidizing agent does not generate any anion species, allowing the low-molecular-weight hydrophobic closed-shell anions contained in the surface modifying liquid (S4) to be selectively attached to the surface of the first electrode.

[0129] The second oxidizing agent can be the same as the third oxidizing agent described later, and compounds preferred as the third oxidizing agent are also preferred as the second oxidizing agent. That is, examples of the second oxidizing agent include quinone compounds having a quinone skeleton, furantrione compounds having a furantrione skeleton, and radical compounds, which are described below as the third oxidizing agent, and are preferably quinone compounds having a quinone skeleton.

[0130] It is particularly preferable that the low-molecular-weight hydrophobic closed-shell anion contained in the surface modifying liquid (S4) is one that is unlikely to undergo an oxidation-reduction reaction with water or an oxidation-reduction reaction with oxygen under temperature conditions of 15°C or higher and 35°C or lower (room temperature conditions) and in the air.

[0131] Preferred examples of such low-molecular-weight hydrophobic closed-shell anions include those exemplified as the low-molecular-weight hydrophobic closed-shell anions generated from the first oxidizing agent, as well as low-molecular-weight hydrophobic closed-shell anions represented by formulas (3F) to (3G).

[0132]

[0133] In the formula, R １４ are each independently a hydrogen atom, a halogen atom, or an optionally substituted fluorinated alkyl group, and are preferably a halogen atom.

[0134] In the formula, R １５ are each independently a perfluoroalkyl group, and two R １５ may be linked to each other to form a ring.

[0135] R １４ Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a chlorine atom or a fluorine atom is preferred, and a fluorine atom is more preferred.

[0136] R １４ The substituents that the fluorinated alkyl group represented by the formula (I) may have include R １ ~R ３Examples of the substituent include, but are not limited to, the same as the substituent that may be possessed by the alkyl group and aryl group represented by the following formula: In addition, in the fluorinated alkyl group, the substituent is a group that substitutes a hydrogen atom bonded to a carbon atom of the fluorinated alkyl group.

[0137] R １４ The number of carbon atoms in the optionally substituted fluorinated alkyl group represented by the formula (I) is not particularly limited, but is preferably 1 or more and 10 or less, more preferably 1 or more and 6 or less, and even more preferably 2 or more and 4 or less.

[0138] R １４ Specific examples of the fluorinated alkyl group represented by the formula (I) which may have a substituent include a trifluoromethyl group, a pentafluoroethyl group, a pentafluoro-n-propyl group, and a 1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl group, and preferably a trifluoromethyl group.

[0139] R １５ The number of carbon atoms in the perfluoroalkyl group represented by the formula (I) is not particularly limited, but is preferably 1 or more and 20 or less, more preferably 1 or more and 12 or less, even more preferably 2 or more and 8 or less, and particularly preferably 2 or more and 6 or less.

[0140] R １５ Specific examples of the perfluoroalkyl group represented by the formula (I) include a perfluoromethyl group (trifluoromethyl group), a perfluoroethyl group, a perfluoro-n-propyl group, a perfluoroisopropyl group, a perfluoro-n-butyl group, a perfluoroisobutyl group, a perfluoro-sec-butyl group, a perfluoro-tert-butyl group, a perfluoro-n-pentyl group, a perfluoroneopentyl group, a perfluoro-n-hexyl group, a perfluorocyclohexyl group, and the like, and preferred are a perfluoromethyl group and a perfluoro-n-butyl group.

[0141] Specific examples of the low-molecular-weight hydrophobic closed-shell anion represented by formula (3F) include tetraphenylborate anion, tetrakis(p-tolyl)borate anion, tetrakis(p-trifluoromethylphenyl)borate anion, tetrakis(p-fluorophenyl)borate anion, tetrakis(perfluorophenyl)borate anion, and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion, and preferably tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion.

[0142] Specific examples of the low-molecular-weight hydrophobic closed-shell anion represented by formula (3G) include bis(trifluoromethanesulfonyl)imide anion, bis(perfluoroethanesulfonyl)imide anion, bis(perfluoropropanesulfonyl)imide anion, bis(perfluorobutanesulfonyl)imide anion, and cyclohexafluoropropane-1,3-bis(sulfonyl)imide anion, and the like, with the bis(trifluoromethanesulfonyl)imide anion being preferred.

[0143] The counter cation of the low-molecular-weight hydrophobic closed-shell anion contained in the surface modifying liquid (S4) is not particularly limited, and examples thereof include protons and metal ions such as lithium ions, sodium ions, and potassium ions. Of these, the counter cation is preferably protons, since this can suppress the deposition of metal salts that inhibit hole injection from the first electrode to the organic semiconductor layer.

[0144] When the counter cation of the low-molecular-weight hydrophobic closed-shell anion is a metal ion, the total concentration of the metal ion in the surface modifying liquid (S3) is preferably 10,000 ppm by mass or less, more preferably 1,000 ppm by mass or less, and even more preferably 100 ppm by mass or less. By keeping the metal ion concentration within this range, it is possible to suppress problems such as the deposition of unnecessary salts on the surface of the first electrode and the diffusion of metal ions into the organic semiconductor layer, which shortens the life of the vertical diode.

[0145] The total concentration of the second oxidizing agent in the surface modifying liquid (S4) is not particularly limited and may be appropriately selected depending on the type of the second oxidizing agent, the shift width of the work function, etc. For example, the total concentration of the second oxidizing agent is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.

[0146] The total concentration of the low-molecular-weight hydrophobic closed-shell anions in the surface modifying liquid (S4) is not particularly limited and may be appropriately selected depending on the type of the low-molecular-weight hydrophobic closed-shell anions, the low-molecular-weight hydrophobic ion coverage rate (described later), the shift width of the work function, etc. For example, the total concentration of the low-molecular-weight hydrophobic closed-shell anions is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.

[0147] When the surface modifying liquid (S4) is used as the surface modifying liquid, holes are injected into the first electrode in this step (i.e., the surface of the first electrode is oxidized), thereby positively charging the surface of the first electrode. Then, low-molecular-weight hydrophobic closed-shell anions electrostatically attach to the positively charged surface of the first electrode, resulting in a surface-modified first electrode. At this time, as in the case of using the surface modifying liquid (S2), low-molecular-weight hydrophobic closed-shell anions electrostatically attach to the surface of the first electrode, forming an anion layer with a thickness of less than a monolayer. The thickness of the anion layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.

[0148] In this way, when the surface modifying liquid (S4) is used as the surface modifying liquid, the surface of the first electrode is modified in the same way as when the surface modifying liquid (S2) is used. Therefore, when the surface modifying liquid (S4) is used as the surface modifying liquid, the work function of the first electrode can be deepened (increased) in the same way as when the surface modifying liquid (S2) is used, and the rectifying characteristics of the vertical diode can be improved. In addition, it is also possible to increase the current density of the vertical diode at low voltages.

[0149] When the first electrode is modified with the surface modifying liquid (S4), a vertical diode with excellent rectification characteristics can be obtained by using a hole-transporting organic semiconductor layer, i.e., a p-type organic semiconductor layer, as the organic semiconductor layer and using the first electrode as a hole-injection electrode (anode (positive electrode)). In this case, the entire organic semiconductor layer does not need to be a p-type organic semiconductor layer; for example, when the organic semiconductor layer has a multilayer structure, the above-mentioned effect can be similarly obtained as long as only the layer adjacent to the first electrode is a p-type organic semiconductor layer.

[0150] When the surface modifying liquid (S4) is used to modify the first electrode, problems such as the formation of an excess layer between the first electrode and the organic semiconductor layer that inhibits hole injection and the generation of salt are effectively suppressed for the same reasons as when the surface modifying liquid (S2) is used. This makes it possible to improve the hole injection from the first electrode to the organic semiconductor layer, and also to realize improved rectification characteristics, longer life, and improved current density at low voltages of the vertical diode.

[0151] (Solvent) The solvent for the surface modifying liquids (S1) to (S4) may be an organic solvent, water, or a mixed solvent of an organic solvent and water. However, from the viewpoints of reducing production costs, improving workability, and reducing the environmental load, water is preferred.

[0152] The water is not particularly limited, and may be tap water; pure water such as distilled water, RO water, and deionized water; or ultrapure water with a resistivity of 18 MΩ or more; but is preferably pure water, and more preferably deionized water. In the present disclosure, RO water means water filtered through a reverse osmosis membrane.

[0153] The organic solvent is not particularly limited as long as it can dissolve or disperse the low-molecular-weight reducing agent or the low-molecular-weight oxidizing agent, and examples thereof include alcohols such as methanol, ethanol, and n-propanol; hydrocarbons such as hexane, benzene, toluene, and xylene; ethers such as diethyl ether, 1,4-dioxane, diglyme, and tetrahydrofuran (THF); esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; halogenated hydrocarbon solvents such as 1,2-dichloroethane and chloroform; nitrile solvents such as acetonitrile and benzonitrile; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methyl-2-pyrrolidone (NMP); and sulfoxides such as dimethyl sulfoxide (DMSO).

[0154] The organic solvent contained in the mixed solvent may be any of the above-mentioned organic solvents that are miscible with water. The water content in the mixed solvent is not particularly limited as long as the two can be uniformly mixed, and may be, for example, in the ranges of 5% by mass or more and less than 100% by mass, 40% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, and 80% by mass or more and 90% by mass or less.

[0155] (Other Components) The surface modifying solutions (S1) to (S4) may contain one or more components other than the above-described components, as long as the effects of the present disclosure are not impaired.

[0156] (Preparation of Surface Modifying Liquid) The surface modifying liquids (S1) and (S2) are prepared by dissolving a first reducing agent and a second oxidizing agent in a solvent, respectively.

[0157] The surface modifying liquid (S3) is prepared by dissolving a second reducing agent and a compound containing a low-molecular-weight hydrophobic cation as a cationic component in a solvent. The compound is preferably a salt formed from the low-molecular-weight hydrophobic cation and an anionic component such as hydroxide ions, halide ions such as chloride ions, bromide ions, and iodide ions, carbonate ions, sulfate ions, and phosphate ions. From the viewpoints of availability and cost, the compound is more preferably a halide salt formed from the low-molecular-weight hydrophobic cation and a halide ion.

[0158] When a halide salt is used to prepare the surface-modifying liquid (S3), the resulting surface-modifying liquid (S3) contains halide ions as counter anions of the low-molecular-weight hydrophobic cations. Therefore, when a halide salt is used to prepare the surface-modifying liquid (S3), it is preferable to dissolve the halide salt in a solvent, bring the resulting solution into contact with an anion exchange resin, and exchange the halide ions in the solution for hydroxide ions, thereby reducing the total concentration of halide ions to the preferred range described above. Any known anion exchange resin can be used as the anion exchange resin.

[0159] The surface modifying liquid (S4) is prepared by dissolving a second oxidizing agent and a compound containing a low-molecular-weight hydrophobic anion as an anion component in a solvent. From the viewpoints of availability and cost, the compound is preferably a metal salt formed from a low-molecular-weight hydrophobic anion and a metal ion such as a lithium ion, a sodium ion, or a potassium ion.

[0160] When a metal salt is used to prepare the surface-modifying liquid (S4), the resulting surface-modifying liquid (S4) contains a metal ion as a counter cation of the low-molecular-weight hydrophobic anion. Therefore, when a metal salt is used to prepare the surface-modifying liquid (S4), it is preferable to bring a solution obtained by dissolving the metal salt in a solvent into contact with a cation exchange resin to exchange the metal ions in the solution for protons, thereby reducing the total concentration of the metal ions to the above-mentioned preferred range. Any known cation exchange resin can be used as the cation exchange resin.

[0161] [1-1-2. First Electrode] In order to obtain good rectification characteristics in a vertical diode, it is generally desirable that the cathode have a work function smaller than the LUMO of the organic semiconductor constituting the organic semiconductor layer and smaller than the work function of the anode. It is also desirable that the anode have a work function larger than the LUMO of the organic semiconductor constituting the organic semiconductor layer.

[0162] Therefore, when the first electrode is a cathode (negative electrode; electron injection electrode), it is desirable that the first electrode, after the electrode modification step, has a work function smaller than the LUMO of the organic semiconductor constituting the organic semiconductor layer (or the organic semiconductor constituting the layer adjacent to the first electrode if the organic semiconductor layer has a multilayer structure) and smaller than the work function of the second electrode. Also, when the first electrode is an anode (positive electrode; hole injection electrode), it is desirable that the first electrode exhibits a work function larger than the second electrode and the organic semiconductor constituting the organic semiconductor layer (or the organic semiconductor constituting the layer adjacent to the second electrode if the organic semiconductor layer has a multilayer structure).

[0163] As described above, the material for the first electrode is appropriately selected depending on the organic semiconductor and the second electrode, but is not particularly limited as long as it is a conductive material, since this process can significantly shift the work function of the first electrode and easily adjust it to a desired work function. Specific electrode materials include, for example, metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, molybdenum, and tungsten; alloys containing two or more of these metals; and metal oxides such as indium oxide, tin oxide, zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO).

[0164] For example, as shown in the examples described below, contact with a surface-modifying solution containing a low-molecular-weight reducing agent can shift the work function of a gold electrode from approximately 5.0 eV to approximately 3.7 eV. Therefore, by using a surface-modified gold electrode, an organic semiconductor layer with a LUMO of approximately 4.0, and an unmodified gold electrode as the first electrode, organic semiconductor layer, and second electrode, respectively, a vertical diode with excellent rectification characteristics, preferably a vertical diode with excellent rectification characteristics and high current density at low voltage, can be obtained. Furthermore, even if the surface-modified gold electrode is replaced with a surface-modified copper electrode or a surface-modified ITO electrode, a vertical diode with excellent rectification characteristics can be obtained based on the same principle.

[0165] Conventionally, electrodes made of precious metals such as gold and silver have typically been used as electrodes for vertical diodes, and copper, ITO, and the like have been considered unsuitable as electrode materials. In contrast, according to the present embodiment, even electrodes made of less expensive materials such as copper and ITO can be suitably used for vertical diodes by subjecting the electrodes to the above-described surface modification. Therefore, the present embodiment can provide a vertical diode with excellent rectification characteristics, in which either or both of the first electrode and the second electrode are copper electrodes or ITO electrodes, preferably a vertical diode in which the first electrode is a copper electrode or ITO electrode.

[0166] The thickness of the first electrode is not particularly limited and may be adjusted appropriately taking into consideration the application of the vertical diode, the device life, etc. Specific examples of the thickness of the second electrode include 10 nm to 200 nm, and preferably 20 nm to 50 nm.

[0167] The second electrode can be produced by any method, such as a known method or a method similar thereto, including, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.

[0168] [1-1-3. Operation Procedure and Conditions] The method for bringing the surface of the first electrode into contact with the surface modifying liquid is not particularly limited and can be appropriately selected from any known solution process, a process equivalent thereto, etc. Known solution processes include, for example, a method in which the first electrode is immersed in the surface modifying liquid, and a method in which the surface modifying liquid is applied to the first electrode by any application method such as spin coating, spray coating, or roll coating.

[0169] The electrode modification step can be carried out in an inert atmosphere such as argon or nitrogen, or in the air. As described above, the surface-modified electrode obtained by this step has high stability to water and the air, and therefore, even if the electrode modification step is carried out by a solution process using an aqueous solution in the air, the effect of the surface modification can be sufficiently obtained. Therefore, in terms of good workability and advantages for industrialization, it is preferable to carry out the electrode modification step in the air.

[0170] The temperature during contact between the surface of the first electrode and the surface modifying liquid is not particularly limited, but is preferably from 5° C. to 50° C., more preferably from 15° C. to 35° C. The time during which the surface of the first electrode is in contact with the surface modifying liquid is not particularly limited, but is preferably from 1 second to 10 hours.

[0171] The contact conditions between the surface of the first electrode and the surface modifying liquid are preferably adjusted so that the proportion of low-molecular-weight hydrophobic ions occupying the surface of the first electrode that is adjacent to the organic semiconductor layer when a vertical diode is fabricated, i.e., the coverage of that surface with a layer of low-molecular-weight hydrophobic ions (hereinafter, sometimes referred to as "low-molecular-weight hydrophobic ion coverage"), falls within the range described below. This is because, by setting the low-molecular-weight hydrophobic ion coverage within the predetermined range, it becomes possible to significantly change the work function of the first electrode.

[0172] The coverage rate of the low-molecular-weight hydrophobic ions can be adjusted by adjusting the concentration of the low-molecular-weight hydrophobic ions, the concentration of the oxidizing agent or reducing agent, and, when the solvent contains water, by adjusting the pH of the solvent, etc. When the electrode surface is oxidized, the coverage rate tends to increase as the pH becomes lower, and when the electrode surface is reduced, the coverage rate tends to increase as the pH becomes higher.

[0173] [1-2. Doping Step] In this embodiment, the organic semiconductor layer of the vertical diode to be manufactured preferably has a doped layer and an undoped layer. Therefore, the manufacturing method according to this embodiment preferably includes a doping step of forming the doped layer by bringing an aqueous solution containing one or more selected from the group consisting of a third oxidizing agent and a third reducing agent and a salt of a dopant ion (hereinafter, sometimes referred to as a "dope solution") into contact with the surface of the organic semiconductor layer precursor. The surface of the organic semiconductor layer that is brought into contact with the dope solution in the doping step is the surface that will be adjacent to the second electrode when the vertical diode is manufactured.

[0174] In the doping step, the doping solution is brought into contact with the surface of the organic semiconductor layer precursor, whereby an oxidation reaction or a reduction reaction of the organic semiconductor proceeds (i.e., carriers are injected into the organic semiconductor layer precursor), and as a result, dopant ions are introduced into the organic semiconductor layer precursor, thereby forming a doped layer. This step can achieve efficient doping even when performed in an air atmosphere.

[0175] Conventionally, chemical doping of organic semiconductors using one or more oxidizing agents and reducing agents has been carried out in an organic solvent system under an inert atmosphere such as argon or nitrogen. The doping method described in WO 2020 / 085342 achieves excellent doping efficiency through chemical doping using ion exchange, resulting in conductive polymers with excellent properties, but the doping must be carried out in an organic solvent system and a nitrogen atmosphere. This is because the oxidizing agents and reducing agents typically used in chemical doping of organic semiconductors are unstable to air and water and are therefore not suitable for chemical doping in an air atmosphere. On the other hand, it has been recognized that oxidizing agents and reducing agents that can be used in the presence of air and water do not have sufficient oxidizing and reducing power to inject carriers into typical organic semiconductors.

[0176] In contrast to this, the doping step in the present embodiment involves the coexistence of a third oxidizing agent that oxidizes an organic semiconductor by electron transfer or proton-conjugated electron transfer, or a third reducing agent that reduces an organic semiconductor by electron transfer or proton-conjugated electron transfer, and a salt of a doping ion in a pH-adjusted aqueous solution, thereby exerting a synergistic effect and enabling chemical doping of an organic semiconductor in the presence of oxygen and water.

[0177] [1-2-1. Doping Solution] The doping solution used in the doping step is an aqueous solution containing at least one selected from the group consisting of a third oxidizing agent and a third reducing agent, and a salt of a dopant ion.

[0178] (Third Oxidizing Agent and Third Reducing Agent) The third oxidizing agent is a compound that injects holes into the organic semiconductor layer precursor and oxidizes the organic semiconductor. The third reducing agent is a compound that injects electrons into the organic semiconductor layer precursor and reduces the organic semiconductor that constitutes the organic semiconductor layer.

[0179] When these compounds oxidize or reduce an organic semiconductor, k protons and k electrons transfer in a concerted manner. k is an integer of 1 or more, preferably 1 to 4, more preferably 1 to 2. For example, as described below, benzoquinone, which is a third oxidizing agent, oxidizes an organic semiconductor through the concerted transfer of two protons and two electrons. As the third oxidizing agent, it is preferable to use two or more third oxidizing agents having different k values ​​in combination. Furthermore, it is preferable to use two or more third reducing agents having different k values ​​in combination. This makes it possible to reduce the influence of external conditions, such as the pH of the dope solution, on doping.

[0180] In the doping step, when a doped layer is formed on a p-type organic semiconductor layer, holes are injected into the organic semiconductor layer precursor by the third oxidizing agent to oxidize the organic semiconductor layer precursor, whereas in the doping step, when a doped layer is formed on an n-type organic semiconductor layer, electrons are injected into the organic semiconductor layer precursor by the third reducing agent to reduce the organic semiconductor layer precursor.

[0181] The third oxidizing agent and the third reducing agent are not particularly limited as long as they are compounds that undergo an oxidation reaction or a reduction reaction by electron transfer or proton-coupled electron transfer, and any compound can be used. Suitable third oxidizing agents include compounds that undergo proton-related oxidation or reduction reactions (i.e., compounds whose redox potential described by the Nernst equation is proportional to pH) and chemical species whose redox potential matches the HOMO level of the organic semiconductor (i.e., chemical species that act as oxidizing agents). Suitable third reducing agents include compounds that undergo proton-related reduction reactions (i.e., compounds whose redox potential described by the Nernst equation is proportional to pH) and chemical species whose redox potential matches the LUMO level of the organic semiconductor (i.e., chemical species that act as reducing agents).

[0182] Examples of the third oxidizing agent include a quinone compound (k=2) having a quinone skeleton; a furantrione compound (k=2) having a furantrione skeleton; and a radical compound; and preferably a quinone compound having a quinone skeleton.

[0183] Examples of the quinone compound include compounds represented by formulas (Q1) to (Q4).

[0184]

[0185] In the formula, R Ｑ１ ~R Ｑ６ are each independently a monovalent functional group; m1 is an integer of 0 to 4; m2 is an integer of 0 to 2; m3 is an integer of 0 to 4; m4 is an integer of 0 to 4; m5 is an integer of 0 to 4; and m6 is an integer of 0 to 4.

[0186] In the formula, R Ｑ１ ~R Ｑ６ are each independently a monovalent functional group. Ｑ１ ~R Ｑ６ may be bonded to each other to form a ring. The ring formed is preferably a 5- to 7-membered ring.

[0187] R Ｑ１ ~R Ｑ６The monovalent functional group represented by the formula (I) is not particularly limited, but examples thereof include an alkyl group (preferably having 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms), an alkenyl group (preferably having 2 to 12 carbon atoms, more preferably 2 to 6 carbon atoms), an aryl group (preferably having 6 to 22 carbon atoms, more preferably 6 to 14 carbon atoms), an aralkyl group (preferably having 6 to 22 carbon atoms, more preferably 6 to 14 carbon atoms), an alkoxy group (preferably having 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms), a hydroxy group, a carboxy group, a mercapto group, an amino group, a halogen atom (such as a chlorine atom or a bromine atom), an alkyl ether group, a carboxylic acid ester group, a sulfonic acid group, a formyl group, a nitro group, a cyano group, and a silyl group. Furthermore, the monovalent functional group may be a group in which the above functional groups are bonded via a divalent linking group such as -O-, -NR-, -S-, -CO-, -COO-, and -CONH-. The alkyl group and alkenyl group may be linear, branched, or cyclic.

[0188] R Ｑ１ ~R Ｑ６ At least one of these is preferably at least one selected from an alkyl group, an alkoxy group, an alkyl ether group, a carboxylic acid ester group, a halogen atom, a hydroxy group, an amino group, a carboxy group, a sulfonic acid group, an aldehyde group, a nitro group, a cyano group, a thiol group, and a silyl group.

[0189] R Ｑ１ ~R Ｑ６ Among these, by making one or more of them hydrophilic groups such as alkoxy groups, hydroxy groups, carboxy groups, sulfonic acid groups, and amino groups, the hydrophilicity of the compound can be adjusted, which is preferable.

[0190] R Ｑ１ ~R Ｑ６ By using one or more of the groups R as an electron-withdrawing group or an electron-donating group, the redox potential of the compound can be adjusted, which is preferable. The electron-withdrawing group increases the oxidizing power of the compound and decreases the reducing power. Conversely, the electron-donating group decreases the oxidizing power of the compound and increases the reducing power. In other words, the R group is selected so as to match the HOMO level or LUMO level of the organic semiconductor to be used. Ｑ１ ~R Ｑ６ can be selected to adjust the redox reaction.

[0191] m1 is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably an integer of 0 to 1. m2 is an integer of 0 to 2, preferably an integer of 0 to 1. m3 is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably an integer of 0 to 1. m4 is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably an integer of 0 to 1. m5 is an integer of 0 to 4, preferably an integer of 1 to 2. m6 is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably an integer of 0 to 1.

[0192] Specific examples of the quinone compound include p-benzoquinone, 2,5-dihydroxy-p-benzoquinone, 2-hydroxy-p-benzoquinone, tetrahydroxy-p-benzoquinone, 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, 2-methyl-p-benzoquinone, 2-methyl-1,4-naphthoquinone, 2,5-dimethoxy-1,4-benzoquinone, 2,5-di-tert-butyl-1,4-naphthoquinone, anthraquinone, etc. Furthermore, the quinone compounds described in JP-A-2018-520455 can also be used as the third oxidizing agent in this embodiment.

[0193] The furantrione compound includes a compound represented by formula (Q5).

[0194]

[0195] In the formula, R Ｑ７ and R Ｑ８ are each a hydrogen atom or a monovalent functional group. Ｑ７ and R Ｑ８ The monovalent functional group represented by R Ｑ１ ~R Ｑ６ The preferred embodiments thereof are also the same as those of the monovalent functional group represented by the formula:

[0196] Specific examples of the compound represented by formula (Q5) include dehydroascorbic acid.

[0197] Examples of radical compounds include 2,2-diphenyl-1-picrylhydrazyl (DPPH), 4-hydroxy-2,2,6,6-tetramethyl-piperidine 1-oxyl (TEMPOL), 2,2,6,6-tetramethyl-piperidinyloxyl (TEMPO), 2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy, free radical (galvinoxyl, free radical), and triphenylmethyl radical.

[0198] The radical compound is preferably a compound containing a radical on an oxygen atom, in that the reaction tends to proceed more efficiently in an aqueous solution, and is more preferably one or more compounds selected from the compound represented by formula (F1) and the compound represented by formula (F2) (k=1).

[0199]

[0200] In the formula, R Ｆ１ is a monovalent functional group; R Ｆ２ is O or S, preferably O.

[0201] R Ｆ１ The monovalent functional group represented by the formula (I) is not particularly limited, but preferred examples include a hydrogen atom, a hydroxy group, a carboxy group, an amino group, a (meth)acryloyl group, a (meth)acrylamide group, a hydrocarbon group having 1 to 20 carbon atoms which may have a hetero atom, and an alkoxy group having 1 to 20 carbon atoms.

[0202] R Ｆ１ is preferably a hydrophilic group, in that the water solubility of the compound represented by formula (F1) is improved. Preferred examples of the hydrophilic group include a hydroxy group, a carboxy group, a (meth)acryloyl group, a (meth)acrylamide group, and an alkoxy group (a methoxy group, an ethoxy group).

[0203] As the compound represented by formula (F1) and the compound represented by formula (F2), synthetic products may be used, or commercially available products such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (methacrylic acid TEMPO), 4-acetamido-TEMPO, 4-hydroxy-TEMPO (TEMPO), 4-oxo-TEMPO, 4-hydroxy-TEMPO benzoate, 4-(2-iodoacetamido)-TEMPO, 4-amino-TEMPO, and 4-carboxy-TEMPO may be used.

[0204] The third oxidizing agent may be used alone or in any combination of two or more kinds in any ratio.

[0205] The third oxidizing agent is preferably one or more selected from a quinone compound and a furantrione compound, is preferably one or more selected from the compounds represented by formulas (Q1) to (Q5), and is preferably one or more selected from the compounds represented by formula (Q1).

[0206] In addition, it is preferable that the compounds represented by formulas (Q1) to (Q5) are contained in the doping solution together with their reduced forms, which allows for more precise control of the redox potentials of the compounds represented by formulas (Q1) to (Q5), and as a result, more precise control of the Fermi level of the organic semiconductor contained in the doping layer.

[0207] Examples of the third reducing agent include hydroquinone compounds (k=2) having a hydroquinone skeleton; dihydroxyfuranone compounds (k=2) having a dihydroxyfuranone skeleton; sugars having reducing properties; and reduced coenzymes; and the like. Preferably, the third reducing agent is one or more selected from the group consisting of hydroquinone compounds having a hydroquinone skeleton and reduced coenzymes, and more preferably a reduced coenzyme.

[0208] Examples of hydroquinone compounds include compounds represented by formulas (Q1') to (Q4'). The compounds represented by formulas (Q1') to (Q4') are reduced forms of the compounds represented by formulas (Q1) to (Q4), respectively.

[0209]

[0210] In the formula, R Ｑ１ ~R Ｑ６ are R in formulas (Q1) to (Q4), respectively. Ｑ１ ~R Ｑ６ The same applies to the preferred embodiments thereof.

[0211] Specific examples of the hydroquinone compound include p-hydroquinone, 1,2,4,5-benzenetetraol, 1,2,4-benzenetriol, benzenehexaol, 1,4-naphthalenediol, 1,2,5-naphthalenetriol, 2-methyl-1,4-benzenediol, 2-methyl-1,4-naphthalenediol, 2,5-dimethoxy-1,4-benzenediol, 2,5-di-tert-butyl-1,4-naphthalenediol, and 9,10-anthracenediol. In addition, the reduced products of the quinone compounds described in JP-A-2018-520455 can also be used as the third reducing agent in this embodiment.

[0212] An example of the dihydroxyfuranone compound is a compound represented by formula (Q5'): The compound represented by formula (Q5') is a reduced form of the compound represented by formula (Q5).

[0213]

[0214] In the formula, R Ｑ７ and R ８ are R in formula (Q5), respectively. Ｑ７ and R ８ The same applies to the preferred embodiments thereof.

[0215] Specific examples of the compound represented by formula (Q5') include ascorbic acid.

[0216] Examples of reducing sugars include fructose, glucose, galactose, maltose, lactose, and cellobiose, with fructose being preferred.

[0217] Examples of reduced coenzymes include reduced flavin mononucleotide (FMNH2), reduced flavin adenine dinucleotide (FADH2), reduced nicotinamide adenine dinucleotide, and reduced nicotinamide adenine dinucleotide phosphate (NADPH), with reduced flavin mononucleotide (FMNH2) being preferred. Reduced coenzymes can be generated by reducing oxidized coenzymes using reducing sugars or the like. For example, when fructose and oxidized flavin mononucleotide (FMN) are dissolved in water, the oxidized flavin mononucleotide accepts electrons from fructose, thereby generating reduced flavin mononucleotide in the system, and this reduced flavin mononucleotide injects electrons into the organic semiconductor layer precursor.

[0218] The third reducing agent may be used alone or in any combination of two or more kinds in any ratio.

[0219] The third reducing agent is preferably one or more selected from hydroquinone compounds and dihydroxyfuranone compounds, preferably one or more selected from compounds represented by formulas (Q1') to (Q5'), and preferably one or more selected from compounds represented by formula (Q1').

[0220] In addition, it is preferable that the compounds represented by formulas (Q1') to (Q5') are contained in the doping solution together with their oxidized forms, which allows for more precise control of the redox potentials of the compounds represented by formulas (Q1') to (Q5'), and as a result, more precise control of the Fermi level of the organic semiconductor contained in the doping layer.

[0221] The dope solution may contain either a third oxidizing agent or a third reducing agent together with a salt of dopant ions, but it is also preferable to contain both a third oxidizing agent and a third reducing agent. This is because the dope solution containing both a third oxidizing agent and a third reducing agent can more stably control the redox potential of the dope solution and the Fermi level of the organic semiconductor. When the dope solution contains both a third oxidizing agent and a third reducing agent, the ratio of the third oxidizing agent to the third reducing agent can be adjusted depending on the carriers and dopant ions to be injected into the organic semiconductor layer precursor.

[0222] The total content of the third oxidizing agent and the third reducing agent in the dope solution is not particularly limited, but is preferably 0.01 to 1,000 mM from the viewpoint of improving doping efficiency. The third oxidizing agent and the third reducing agent contained in the dope solution are preferably completely dissolved in water as a solvent, but may be partly contained in the dope solution in a solid state.

[0223] (Dopant ion salt) The dopant ion salt is a coexisting salt of a dopant ion that is ultimately introduced into the organic semiconductor layer and a spectator ion that is its counter ion. The dopant ion is preferably a closed-shell ion, more preferably a hydrophobic closed-shell ion. The spectator ion is an ion that is not introduced into the organic semiconductor.

[0224] When the organic semiconductor layer is a p-type organic semiconductor layer, the dopant ion is preferably a closed-shell anion capable of forming a salt with a spectator ion, and more preferably a hydrophobic closed-shell anion capable of forming a salt with a spectator ion.

[0225] Examples of such dopant ions include bis(trifluoromethanesulfonyl)imide ion (TFSI ion), tetrafluoroborate ion (BF ４ － ), hexafluorophosphate ion (PF ６ － ), hexafluoroantimonate ion (SbF ６ －), carbonate ion, sulfonate ion, nitrate ion, phosphate ion, thiocyanate ion, cyanate ion, chloride ion, bromide ion, iodide ion, triiodide ion, fluoride ion, trifluoro[tris(pentafluoroethyl)]phosphate ion (FAP ion), bis(pentafluoroethanesulfonyl)imide ion (TFESI ion), bis(oxalato)borate ion (BOB ion), bis(malonate)borate ion (MOB ion), tetrakis(pentafluorophenyl)borate ion (PFPB ion), tetrakis(3,5-trifluoromethyl)phenylborate ion (TtFPB ion), tetrakis(pentafluorophenyl)borate ion (TFPB), and iron tetrachloride ion (FeCl ４ － ) and the like; and derivatives thereof; and the like.

[0226] According to the doping process of this embodiment, dopant ions can be introduced into the organic semiconductor layer regardless of the type of dopant ion. The dopant ions may be appropriately selected depending on the properties of the organic semiconductor. For example, from the viewpoint of imparting superior stability to the doped organic semiconductor layer, the doping ions are preferably anions such as TFSI ions and FAP ions, which have more delocalized negative charges. On the other hand, if there is a purpose such as preventing the inclusion of a specific element (e.g., fluorine atom) in the doped organic semiconductor layer, sulfonate ions, sulfate ions, etc. may also be used.

[0227] When the organic semiconductor layer is a p-type organic semiconductor layer, the spectator ion is preferably a cation with a closed shell structure that can form a salt with the dopant ion.

[0228] Examples of such spectator ions include ions of metals such as Li, Na, Cs, Mg, Ca, Cu, and Ag; metal ions of these metals modified with cyclic ethers or the like; organic molecular ions such as imidazolium, morpholinium, piperidinium, pyridinium, pyrrolidinium, ammonium, and phosphonium; and derivatives of these organic molecular ions.

[0229] When the organic semiconductor layer is an n-type organic semiconductor layer, the dopant ion is preferably a closed-shell cation capable of forming a salt with a spectator ion, and more preferably a hydrophobic closed-shell cation capable of forming a salt with a spectator ion.

[0230] Examples of such dopant ions include ions of metals such as Li, Na, Cs, Mg, Ca, Cu, and Ag; ions of these metals modified with cyclic ethers or the like; organic molecular ions such as imidazolium, morpholinium, piperidinium, pyridinium, pyrrolidinium, ammonium, and phosphonium; and derivatives of these organic molecular ions.

[0231] When the organic semiconductor layer is an n-type organic semiconductor layer, the spectator ion is preferably a closed-shell anion capable of forming a salt with the dopant ion.

[0232] Such spectator ions include BF ４ － , P.F. ６ － , SbF ６ － , carbonate ion, sulfonate ion, nitrate ion, phosphate ion, thiocyanate ion, cyanate ion, chloride ion, bromide ion, iodide ion, triiodide ion, fluoride ion, FAP ion, TFSI ion, TFESI ion, BOB ion, MOB ion, PFPB ion, TtFPB ion, TFPB ion, and FeCl ４ － and the like; and derivatives thereof; and the like.

[0233] The salt of the doping ion may be used alone or in any combination of two or more kinds in any ratio.

[0234] The total content of the salt of the doping ion in the doping solution is not particularly limited, but is preferably 0.01 mM to 1,000 mM. The salt of the doping ion may be present in the aqueous solution in a state where at least a part of it is dissolved in the water solvent, or a part of it may be present as a solid.

[0235] (Solvent) The water solvent is not particularly limited, and examples thereof include tap water; pure water such as distilled water, RO water, and deionized water; and ultrapure water with a resistivity of 18 MΩ or more; however, pure water is preferred, and deionized water is more preferred.

[0236] (pH) The pH of the doping solution is not particularly limited, but since the doping amount of the organic semiconductor depends on the pH of the doping solution, it is preferable to adjust the pH of the doping solution to achieve a desired doping amount. By controlling the doping amount of the organic semiconductor by adjusting the pH of the doping solution, the Fermi level of the organic semiconductor can be precisely controlled. In the present disclosure, pH refers to the pH at 25°C.

[0237] In addition, it is preferable to adjust the pH of the dope solution in advance so that the redox potentials of the third oxidizing agent and the third reducing agent can be adjusted to a level at which carrier transfer can occur between the third oxidizing agent and the third reducing agent and the organic semiconductor. The third oxidizing agent and the third reducing agent used in this embodiment are compounds that oxidize and reduce the organic semiconductor by electron transfer or proton-conjugated electron transfer, respectively. The redox potentials of such compounds can be precisely and easily adjusted by adjusting the pH of the dope solution. Note that when a one-electron oxidizing agent or a one-electron reducing agent that does not involve proton transfer is used, the above-mentioned adjustment is difficult.

[0238] Figure 3 is a diagram plotting the change in the redox potential of benzoquinone / hydroquinone (hereinafter referred to as "HQ / BQ") with pH on an equilibrium diagram of the redox potential of water versus pH. As can be seen from Figure 3, the redox potential of HQ / BQ can be adjusted within a range that does not involve a reaction with water, so the reactivity can be adjusted appropriately depending on the type of organic semiconductor, etc.

[0239] The preferred range of pH of the dope solution varies depending on the type of organic semiconductor, the type of third oxidizing agent, the type of third reducing agent, the content of the third oxidizing agent, the content of the third reducing agent, etc., but can be easily determined by a spectroscopic method, an electrochemical method, a quantum chemical calculation, etc. The procedure for setting the preferred range of pH of the dope solution will be described below.

[0240] First, the redox potentials of the third oxidizing agent and the third reducing agent can both be expressed relative to the vacuum level or the electrode potential of a reference electrode such as silver-silver chloride. For example, this value for BQ / HQ is publicly known.

[0241] Furthermore, if the pH is changed by 1, the redox potential of BQ / HQ shifts by 59 meV, and even if the concentration ratio of BQ / HQ ([BQ] / [HQ]) is changed by two orders of magnitude, the redox potential still shifts by 59 meV. When using other oxidizing agents and reducing agents, the quantitative difference between the redox potential at a given pH and BQ / HQ can be evaluated by cyclic voltammetry. This method is well known, and the evaluation results themselves are often publicly known in the literature, so there are no technical difficulties in measurement and investigation.

[0242] The doping of the p-type organic semiconductor layer can be carried out by adjusting the relationship between the redox potential of the third oxidizing agent and the ionization potential of the p-type organic semiconductor.

[0243] The ionization potential of p-type organic semiconductors can be easily measured by photoelectron yield spectroscopy, cyclic voltammetry, etc., and many values ​​measured by similar methods have been reported in the literature, so there are no technical difficulties in measuring and investigating them.

[0244] In doping the n-type organic semiconductor layer, the relationship between the redox potential of the third reducing agent and the electron affinity of the n-type organic semiconductor may be adjusted.

[0245] The electron affinity of n-type organic semiconductors can be estimated from information obtained by combining ionization potential measurements by photoelectron yield spectroscopy with band gap measurements (optical absorption measurements), and can also be evaluated by cyclic voltammetry. This information has also been widely reported in the literature, and there are no technical difficulties in measuring and investigating it.

[0246] As described above, the preferred pH range of the doping solution can be determined based on the redox potential, ionization potential, and electron affinity. The redox potential, ionization potential, and electron affinity may be values ​​estimated by density functional theory calculations.

[0247] The pH of the dope solution may be adjusted by adding agents such as pH adjusters, such as acids and bases, and pH buffers.

[0248] [1-2-2. Operation Procedure and Conditions] The method for bringing the dope solution into contact with the surface of the organic semiconductor layer is not particularly limited and can be appropriately selected from any known solution process or a process similar thereto. Examples of known solution processes include a method of immersing the organic semiconductor layer in a surface modifying liquid, and a method of applying the dope solution to the organic semiconductor layer by any coating method such as spin coating, spray coating, or roll coating.

[0249] The doping step can be carried out in an inert atmosphere such as argon or nitrogen, or in the air. However, it is preferable to carry out the doping step in the air, as this provides good workability and is advantageous for industrialization.

[0250] The temperature during contact between the surface of the first electrode and the surface modifying liquid is not particularly limited, but is preferably from 5° C. to 50° C., more preferably from 15° C. to 35° C. The time during which the surface of the first electrode is in contact with the surface modifying liquid is not particularly limited, but is preferably from 1 second to 10 hours.

[0251] [1-2-3. Estimated Doping Mechanism] The estimated doping mechanism in the doping process will be explained with reference to the drawings.

[0252] 1 and 2 show an example in which poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14, also simply referred to as "PBTTT") is used as the p-type organic semiconductor and benzoquinone is used as the third oxidant. In this example, the aqueous solution contains not only benzoquinone (BQ), which is the third oxidant, but also its redox pair, hydroquinone (HQ). The structures of PBTTT and BQ / HQ are as follows:

[0253]

[0254]

[0255] Figure 1 shows an energy diagram of PBTTT and BQ / HQ. The vertical axis represents energy relative to the vacuum level. The redox potential of BQ / HQ can be easily adjusted by adjusting the pH of the aqueous solution, and in relation to PBTTT, electron transfer (ET) can occur. In other words, BQ / HQ can act as a third oxidizing agent for PBTTT.

[0256] In the doping step, doping is thought to occur according to the mechanism shown in FIGS. 2(A) to 2(C).

[0257] First, BQ / HQ and dopant anion Y － When the PBTTT layer comes into contact with a doping solution containing a salt of BQ and a counter cation (spectator ion; not shown), at least a portion of the BQ receives two protons from the aqueous solution and two electrons from PBTTT, resulting in reduction to HQ (Fig. 2(A)). Meanwhile, PBTTT is oxidized, i.e., holes, which are carriers, are injected into the PBTTT layer, and the surface of the PBTTT layer becomes positively charged (Fig. 2(A)).

[0258] Then, due to electrostatic interactions, the dopant ions Y in the doping solution － are introduced from the positively charged surface of the organic semiconductor layer (FIG. 2B). As a result, holes and dopant ions Y are introduced into the region including the surface of the PBTTT layer. － A doped layer is formed by introducing the above (FIG. 2(C)).

[0259] The following formulas are model reactions occurring at each stage of the doping process. Reaction (i) occurs at the stage shown in Figure 2(A). Reactions (ii) and (iii) occur at the stages shown in Figure 2(B) and Figure 2(C).

[0260]

[0261] The above-mentioned estimated mechanism relates to the case where holes and dopant anions are introduced into a p-type organic semiconductor layer. The estimated doping mechanism is similar when electrons and dopant cations are introduced into an n-type organic semiconductor layer. Furthermore, although the estimated doping mechanism has been explained using an example in which BQ with k = 2 was used as the third oxidizing agent, the estimated doping mechanism is also similar when k is other than 2.

[0262] [1-2-4. Organic semiconductor layer precursor and organic semiconductor layer] The organic semiconductor layer precursor to be doped in the doping step will be described. In an embodiment in which the manufacturing method according to the present embodiment does not include a doping step, the "organic semiconductor layer precursor to be doped" is a layer that is directly incorporated into the vertical diode as the "organic semiconductor layer". In the present disclosure, the "organic semiconductor layer" may be used as a concept that includes the "organic semiconductor layer precursor", and the "organic semiconductor layer precursor" may be used as a concept that includes the "organic semiconductor layer".

[0263] The organic semiconductor layer precursor is a layer formed of an organic semiconductor and has a single-layer structure or a multilayer structure. The layer structure of the organic semiconductor layer precursor and the type of organic semiconductor constituting the organic semiconductor layer precursor may be appropriately selected depending on the surface modification of the first electrode, the types of carriers and dopant ions to be injected into the organic semiconductor layer precursor in the doping step, and the like.

[0264] For example, when a low-molecular-weight hydrophobic cation is attached to the first electrode in the electrode modification step, the organic semiconductor layer precursor may be a single-layer n-type organic semiconductor layer precursor; a two-layer organic semiconductor layer precursor in which an n-type organic semiconductor layer and a p-type organic semiconductor layer are stacked from the first electrode to the second electrode; or a three-layer organic semiconductor layer precursor in which an n-type organic semiconductor layer, an i-type organic semiconductor layer, and a p-type organic semiconductor layer are stacked from the first electrode to the second electrode. In this case, when the layer to be doped is a p-type organic semiconductor layer, it is preferable to use the organic semiconductor layer precursor of the above-mentioned two-layer or three-layer structure so that holes and dopant anions are injected into the p-type organic semiconductor layer. Even when a low-molecular-weight hydrophobic cation is attached to the first electrode in the electrode modification step, as described above, a suitable organic semiconductor layer precursor can be selected based on the mechanism of the diode.

[0265] The organic semiconductor constituting the organic semiconductor layer precursor may be a low molecular weight compound or a high molecular weight compound.

[0266] Examples of p-type low molecular weight compounds include condensed polycyclic compounds, triarylamine compounds, five-membered heterocyclic compounds, phthalocyanine compounds, porphyrin compounds, carbon nanotubes, and graphene.

[0267] Examples of condensed polycyclic compounds include anthracene, tetracene, pentacene, anthradithiophene, and hexabenzocoronene, which may have a substituent.

[0268] Examples of triarylamine compounds include 4,4',4"-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), 4,4',4"-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (TPD), 1,3-bis(9-carbazolyl)benzene (mCP), and 4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP).

[0269] Examples of the five-membered heterocyclic compound include oligothiophene and tetrathiafulvalene (TTF), which may have a substituent.

[0270] Examples of the phthalocyanine compound include metal complexes of phthalocyanine, naphthalocyanine, anthracyanine, and tetrapyrazinoporphyrazine, which may have a substituent.

[0271] Examples of the porphyrin compound include metal complexes of porphyrin which may have a substituent.

[0272] As a p-type low molecular weight compound, 3,11-dioctyldinaphtho[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (C ８ -DNBDT), 3,11-didecyldinaphtho[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (C １０ -DNBDT), 3,9-dihexyldinaphtho[2,3-b;2',3-d]thiophene (C ６ -DNT), 2,9-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C １０ -DNTT), 2,7-dioctylbenzothieno[3,2-b][1]benzothiophene (C ８ -BTBT), and 6,13-bis(triisopropylsilylethynyl)pentacene, etc. are preferred.

[0273] Examples of n-type low molecular weight compounds include fullerene compounds, electron-deficient phthalocyanine compounds, condensed polycyclic compounds (such as naphthalene tetracarbonyl compounds and perylene tetracarbonyl compounds), TCNQ compounds (tetracyanoquinodimethane compounds), and graphene.

[0274] As the fullerene compound, C ６０ , C ７０ , C ７６ , C ７８ , C ８０ , C ８２ , C ８４ , C ８６ , C ８８, C ９０ , C ９６ , C １１６ , C １８０ , C ２４０ , C ５４０ and PCBM, and preferably C ６０ , C ７０ , C ８６ or PCBM, which may have a substituent.

[0275] Examples of electron-deficient phthalocyanine compounds include metal complexes of phthalocyanine compounds such as phthalocyanine, naphthalocyanine, anthracyanine, and tetrapyrazinoporphyrazine, to which four or more electron-withdrawing groups are bonded. These may have a substituent. Examples of electron-deficient phthalocyanine compounds include fluorinated phthalocyanine (F １６ MPc) and chlorinated phthalocyanine (Cl １６ M represents a central metal, and Pc represents phthalocyanine.

[0276] Examples of naphthalene tetracarbonyl compounds include naphthalene tetracarboxylic anhydride (NTCDA), naphthalene bisimide compounds (NTCDI), and perinone pigments (Pigment Orange 43, Pigment Red 194, etc.).

[0277] Examples of perylene tetracarbonyl compounds include perylene tetracarboxylic anhydride (PTCDA), perylene bisimide compounds (PTCDI), and benzimidazole fused compounds (PV).Specific examples of perylene tetracarbonyl compounds include dicyanoperylene-3,4:9,10-bis(dicarboximide).

[0278] Examples of TCNQ compounds include TCNQ, TCNQ, and compounds in which the benzene ring moiety of these compounds is replaced with another aromatic ring or heterocycle. Specific examples of TCNQ compounds include TCNQ (tetracyanoquinodimethane), TCNAQ (tetracyanoanthraquinodimethane), and TCN3T (2,2'-((2E,2"E)-3',4'-alkyl-substituted-5H,5"H-[2,2':5',2"-terthiophene]-5,5"-diyldiene) dimalononitrile derivatives).

[0279] The polymer compound may be a π-conjugated polymer, such as polythiophene, polyselenophene, polypyrrole, polyparaphenylene, polyparaphenylenevinylene, polythiophenevinylene, or polyaniline, which may have a substituent.

[0280] Examples of p-type polymer compounds include [poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]] (PBTTT-C14), poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-ortho-5,5-(2,5-di(thie-2-yl)thieno[3,2-b]thiophene)] (Poly[2,5-(2-oc

[0033] Examples of suitable diketopyrrolopyrrole copolymers include poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)] (PDPP2T-TT-OD)), and poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-o-(di(thienothie-2-yl)thiophene)] (PDPP2TT-T).

[0281] Examples of n-type polymer compounds include poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-o-5,5'-(2,2'-bithiophene)} (N2200) and poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)).

[0282] The organic semiconductor may be used alone or in any combination of two or more kinds in any ratio.

[0283] The organic semiconductor may be crystallized. In particular, when the organic semiconductor is a low molecular weight compound, the organic semiconductor is preferably a single crystal. Furthermore, when the organic semiconductor is a high molecular weight compound, the high molecular weight compound may be molecular oriented.

[0284] The method for producing the organic semiconductor layer precursor is not particularly limited, and any method such as a known method or a method similar thereto can be adopted.As a known method, for example, a method in which a composition layer is formed by a coating method using a composition containing an organic semiconductor and a solvent, and the solvent is removed from the composition layer to obtain the organic semiconductor layer precursor.When the organic semiconductor layer precursor has a multilayer structure, the organic semiconductor layer precursor can be produced by repeating the cycle of forming the above-mentioned composition layer and removing the solvent from the composition layer multiple times.

[0285] The solvent contained in the composition is not particularly limited as long as it can dissolve the organic semiconductor, and examples thereof include aromatic organic solvents such as dichlorobenzene, acetonitrile, butyl acetate, and fluoroalcohols. The content of the organic semiconductor in the composition may be adjusted appropriately depending on the desired thickness of the organic semiconductor layer precursor, and is preferably 0.1% by mass or more and 99% by mass or less.

[0286] Other known methods include the methods described in paragraphs 0025 to 0033 of International Publication No. 2020 / 085342; and the methods described in paragraphs 0026 to 0029 of Japanese Patent Laid-Open No. 2020-38133.

[0287] The thickness of the organic semiconductor layer precursor (total thickness when the organic semiconductor layer precursor has a multilayer structure) is not particularly limited and may be appropriately adjusted taking into consideration the application of the vertical diode, the element life, etc. Specific examples of the thickness of the organic semiconductor layer precursor include 11 nm to 300 nm, preferably 12 nm to 70 nm, more preferably 15 nm to 50 nm, even more preferably 18 nm to 40 nm, and particularly preferably 20 nm to 30 nm. In addition, in an embodiment in which the manufacturing method according to the present embodiment does not include a doping step, the "organic semiconductor layer precursor" referred to here is a layer that is incorporated into the vertical diode as an "organic semiconductor layer" either doped or as is, and therefore the total thickness of the organic semiconductor is also as described above.

[0288] In this embodiment, the ion layer that contributes to improving the rectification characteristics is not dispersed in the organic semiconductor layer but is present at the interface between the first electrode and the organic semiconductor layer, so a high rectification ratio can be achieved even if the organic semiconductor layer is thin, regardless of the presence or absence of a doped layer. More specifically, while the organic semiconductor layer of a conventional vertical diode typically has a thickness of about 100 nm, in the examples described below, a vertical diode that exhibits good rectification characteristics was obtained even though the organic semiconductor layer was 25 nm thick.

[0289] [1-3. Lamination Step] In this embodiment, the first electrode, the organic semiconductor layer, and the second electrode are laminated adjacent to each other in this order. At this time, the first electrode and the organic semiconductor layer are laminated so that the surface of the first electrode modified in the electrode modification step comes into contact with the organic semiconductor layer. Furthermore, if a doped layer is formed on the organic semiconductor layer in the doping step, the organic semiconductor layer and the second electrode are laminated so that the doped layer comes into contact with the second electrode.

[0290] The method for laminating each layer is not particularly limited as long as the layers are laminated in an order that satisfies the above-mentioned conditions, and any method such as a known method or a method similar thereto can be used.

[0291] For example, lamination may be performed by preparing a first electrode, modifying the surface of the first electrode, preparing an organic semiconductor layer on the surface-modified first electrode, and preparing a second electrode on the organic semiconductor layer. Alternatively, lamination may be performed by preparing a second electrode, preparing an organic semiconductor layer on the second electrode, and disposing the surface-modified first electrode on the organic semiconductor layer. Examples of methods for preparing an organic semiconductor layer include the wet method described above in the section [1-2-4. Organic Semiconductor Layer Precursor and Organic Semiconductor Layer]. Alternatively, lamination of the organic semiconductor layer may be performed by a transfer method in which an organic semiconductor layer is prepared on a transfer substrate, the organic semiconductor layer is transferred onto one of the surface-modified first and second electrodes, and the other electrode is prepared on the organic semiconductor layer.

[0292] When the production method according to this embodiment includes a doping step, the lamination may be performed, for example, by preparing a first electrode, modifying the surface of the first electrode, preparing an organic semiconductor layer precursor on the surface-modified first electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a second electrode on the doped layer formed by the doping step; alternatively, the lamination may be performed by preparing a second electrode, transferring the organic semiconductor layer on which the doped layer has been formed by the doping step from a transfer substrate onto the second electrode, and arranging the surface-modified first electrode on the undoped layer of the organic semiconductor layer.

[0293] [1-3-1. Second Electrode] The following describes the material of the second electrode to be laminated together with the organic semiconductor layer and a method for producing the second electrode. The second electrode is an anode when the first electrode is a cathode, and is a cathode when the first electrode is an anode.

[0294] As described above in the section [1-1-2. First Electrode], when the second electrode is an anode, it is desirable that the second electrode exhibit a work function larger than that of the organic semiconductor constituting the organic semiconductor layer and the first electrode. Furthermore, when the second electrode is a cathode, it is desirable that the second electrode have a work function smaller than the LUMO of the organic semiconductor and smaller than that of the first electrode.

[0295] The material for the second electrode is not particularly limited and may be appropriately selected from conductive materials depending on the type of the first electrode and the organic semiconductor. Specific electrode materials include those exemplified as materials for the unmodified first electrode.

[0296] The thickness of the second electrode is not particularly limited and may be adjusted appropriately taking into consideration the application of the vertical diode, the element life, etc. Specific examples of the thickness of the second electrode include 10 nm to 200 nm, and preferably 20 nm to 50 nm.

[0297] The second electrode is formed to a predetermined thickness by any known method or a method equivalent thereto, and is laminated with other layers. Known methods for forming the second electrode include, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.

[0298] When another layer is laminated on the first electrode, the first electrode is preferably formed on a substrate, and the same applies when another layer is laminated on the second electrode.

[0299] The substrate is not particularly limited as long as it can form the first electrode or the second electrode, but it is preferable that it does not chemically react with the organic semiconductor that constitutes the organic semiconductor layer. Examples of such substrates include a glass substrate and a silicon substrate.

[0300] [1-4. Other Steps] The production method according to this embodiment may include other steps in addition to the steps described above. Examples of other steps include a step of washing the surface-modified first electrode after the electrode modification step, and a step of washing the doped organic semiconductor layer after the doping step.

[0301] Alternatively, the manufacturing method according to this embodiment may include, in addition to or instead of the doping step, a step of doping the organic semiconductor layer by any known method such as those disclosed in International Publication No. 2020 / 085342 or a method equivalent thereto.

[0302] [2. Vertical Diode] A second embodiment of the present disclosure is a vertical diode in which a first electrode, an organic semiconductor layer, and a second electrode are stacked adjacent to each other in this order, and low-molecular-weight hydrophobic ions are attached to a surface of the first electrode that is adjacent to the organic semiconductor layer. The vertical diode according to this embodiment can be manufactured by the manufacturing method according to the first embodiment. Furthermore, the vertical diode according to this embodiment has excellent rectification characteristics and can therefore be suitably used as a rectifying diode.

[0303] 4A, the vertical diode 10 according to this embodiment is a vertical diode in which a first electrode 12, an organic semiconductor layer 14, and a second electrode 18 are stacked adjacent to each other in this order. Low-molecular-weight hydrophobic ions 13 are attached to the surface of the first electrode 12 that is adjacent to the organic semiconductor layer 14.

[0304] The low-molecular-weight hydrophobic ions are electrostatically attached to the surface of the first electrode by the electrode modification step in the first embodiment. That is, the low-molecular-weight hydrophobic ions are any of low-molecular-weight hydrophobic cations and / or other low-molecular-weight hydrophobic cations derived from the first reducing agent contained in the surface-modifying liquid (S1); low-molecular-weight hydrophobic anions and / or other low-molecular-weight hydrophobic anions derived from the first oxidizing agent contained in the surface-modifying liquid (S2); low-molecular-weight hydrophobic closed-shell cations contained in the surface-modifying liquid (S3); and low-molecular-weight hydrophobic closed-shell anions contained in the surface-modifying liquid (S4). Therefore, the explanation of the low-molecular-weight hydrophobic ions in the section [1-1-1. Surface-modifying liquid] is incorporated herein by reference.

[0305] In the vertical diode, the coverage of the low-molecular-weight hydrophobic ions is preferably 10 area % or more and 50 area % or less, more preferably 15 area % or more and 40 area % or less, and even more preferably 20 area % or more and 30 area % or less. When the coverage of the low-molecular-weight hydrophobic ions is within the above range, a first electrode having a work function significantly shifted compared to that before surface modification can be obtained, and the shifted work function can be maintained even in an air atmosphere.

[0306] After the surface modification of the first electrode, some of the molecular hydrophobic ions attached to the surface of the first electrode may diffuse into the organic semiconductor layer during the process of producing the vertical diode or during storage of the vertical diode. However, the preferred range of the coverage of the small molecular hydrophobic ions is as described above, both immediately after the surface modification of the first electrode and after the production of the vertical diode.

[0307] The coverage of the low-molecular-weight hydrophobic ions can be measured by X-ray photoelectron spectroscopy (XPS). By analyzing the spectral intensity derived from atoms originating from the electrode and the spectral intensity derived from atoms of the low-molecular-weight hydrophobic ions, the coverage and the film thickness of the low-molecular-weight hydrophobic ion layer can be determined.

[0308] As described above, in this embodiment, the formation of salts between low-molecular-weight hydrophobic ions and counter ions on the surface of the first electrode is suppressed. It is preferable that the low-molecular-weight hydrophobic ions do not form salts with any of the counter ions, including ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, and ions of the metal contained in the first electrode.

[0309] More specifically, among the low-molecular-weight hydrophobic ions attached to the surface of the first electrode adjacent to the organic semiconductor layer, the proportion of low-molecular-weight hydrophobic ions forming salts with counter ions is preferably 0 mol% or more and 25 mol% or less, more preferably more than 0 mol% and 20 mol% or less, even more preferably 0 mol% or more and 15 mol% or less, and particularly preferably 5 mol% or more and 10 mol% or less.

[0310] The proportion of the low-molecular-weight hydrophobic ions that form salts with counter ions on the surface of the first electrode can be measured by X-ray photoelectron spectroscopy (XPS). By analyzing the spectral intensity derived from the counter ion atoms and the spectral intensity derived from the low-molecular-weight hydrophobic ions, it is possible to evaluate the proportion of the low-molecular-weight hydrophobic ions that form salts.

[0311] As shown in FIG. 4B , in the vertical diode 10 according to this embodiment, the organic semiconductor layer 14 preferably includes a doped layer 17 and an undoped layer 15. The doped layer 17 is formed as the outermost layer of the organic semiconductor layer 14 and is adjacent to the second electrode 18. This doped layer 17 is formed by injecting carriers (electrons or holes) and dopant ions into the organic semiconductor layer precursor in the doping step according to the first embodiment. In this embodiment, the organic semiconductor layer preferably includes a doped layer and an undoped layer. The undoped layer may have a single-layer structure or a multilayer structure.

[0312] The dopant ions contained in the doped layer are derived from salts of the dopant ions contained in the dope solution and have the opposite polarity to the carriers. Therefore, when the carriers contained in the doped layer are holes, the dopant ions contained in the doped layer are dopant anions. When the organic semiconductor layer has such a doped layer, it is preferable that the low-molecular-weight hydrophobic ions modifying the surface of the first electrode are low-molecular-weight hydrophobic cations, in terms of improving the rectification characteristics of the vertical diode and improving the current density at low voltage.

[0313] On the other hand, when the carriers contained in the doped layer are electrons, the dopant ions contained in the doped layer are dopant cations. When the organic semiconductor layer has such a doped layer, it is preferable that the low-molecular-weight hydrophobic ions modifying the surface of the first electrode are low-molecular-weight hydrophobic anions, in terms of improving the rectification characteristics of the vertical diode and improving the current density at low voltage.

[0314] When a hole-transporting organic semiconductor layer, i.e., a p-type organic semiconductor layer, is used as the organic semiconductor constituting the doped layer, holes and dopant anions are injected into the doped layer, thereby providing a vertical diode with excellent rectification characteristics and high current density at low voltage. On the other hand, when an electron-transporting organic semiconductor layer, i.e., an n-type organic semiconductor layer, is used as the organic semiconductor constituting the doped layer, electrons and dopant cations are injected into the doped layer, thereby providing a vertical diode with excellent rectification characteristics and high current density at low voltage.

[0315] It is preferable that the dopant ions contained in the doped layer do not form salts with counter ions, and it is more preferable that the dopant ions do not form salts with any counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, and ions of the metal contained in the second electrode.

[0316] More specifically, among the dopant ions contained in the doped layer, the proportion of dopant ions that form salts with counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, or ions of the metal contained in the second electrode is preferably 0 mol% or more and 25 mol% or less, more preferably more than 0 mol% and 20 mol% or less, even more preferably 0 mol% or more and 15 mol% or less, and particularly preferably 5 mol% or more and 10 mol% or less.

[0317] The proportion of dopant ions that form salts with counter ions can be measured by X-ray photoelectron spectroscopy (XPS).

[0318] In this embodiment, in the organic semiconductor layer precursor, a region from the surface of the organic semiconductor layer precursor in contact with the doping solution to the depth reached by the carriers and dopant ions becomes a doped layer, and the remaining region becomes an undoped layer. Note that the depth reached by the carriers and dopant ions is usually the thickness T of the doped layer. ｄ is equivalent to

[0319] Doped layer thickness T ｄis not particularly limited, but is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more and 20 nm or less, even more preferably 3 nm or more and 15 nm or less, and even more preferably 4 nm or more and 10 nm or less. ｄ The total thickness of the organic semiconductor layer T ｏ The thickness of the undoped layer T subtracted from ｕ is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 50 nm or less, even more preferably 12 nm or more and 30 nm or less, and even more preferably 15 nm or more and 25 nm or less. ｄ By setting the value of the current flowing in the forward direction to be within the above range, it is possible to increase the value of the current flowing in the forward direction while maintaining rectification.

[0320] Undoped layer T ｕ The thickness of the undoped layer T can be estimated by capacitance measurement, and the thickness of the undoped layer T can be estimated by contact step height measurement. ｕ If the thickness of the doped layer can be determined, the thickness of the doped layer can also be estimated.

[0321] The undoped layer is a layer into which carriers and dopant ions are not implanted during the doping process in the first embodiment. However, since dopant ions in the doped layer may diffuse into the region during the manufacturing process after the doping process and during storage of the vertical diode, in this disclosure, a layer that acts as a resistive component in capacitance measurement is referred to as a "doped layer" and a layer that acts as a capacitive component is referred to as an "undoped layer." Furthermore, although the undoped layer 15 in FIG. 4B is illustrated as a single layer, the undoped layer may have a multilayer structure.

[0322] The vertical diode according to this embodiment can efficiently convert high-frequency AC power into DC power. In this disclosure, "high frequency" means a frequency of 10 MHz or higher (e.g., 10 MHz, 100 MHz, or 1 GHz).

[0323] More specifically, the vertical diode according to this embodiment has a conversion efficiency (AC-DC conversion efficiency) for converting 10 MHz AC power into DC power of preferably 4% or more, more preferably 5% or more, and even more preferably greater than 5%. Alternatively, the vertical diode according to this embodiment has a conversion efficiency (AC-DC conversion efficiency) for converting 1 GMz AC power into DC power of preferably 4% or more, more preferably 5% or more, and even more preferably greater than 5%.

[0324] As a specific layer structure of the vertical diode according to this embodiment, in which low-molecular-weight hydrophobic cations are attached to the surface of the first electrode, for example, the layer structures shown in (A1) to (A5) below are preferably exemplified. Although not described in (A1) to (A5) below, the first electrode or the second electrode is usually formed on a substrate 11, as shown in Figures 4(A) and 4(B).

[0325] (A1) First electrode / n-type organic semiconductor layer / second electrode (A2) First electrode / n-type organic semiconductor layer / p-type organic semiconductor layer / second electrode (A3) First electrode / n-type organic semiconductor layer / p-type organic semiconductor layer (doped layer) / second electrode (A4) First electrode / n-type organic semiconductor layer / i-type organic semiconductor layer / p-type organic semiconductor layer / second electrode (A5) First electrode / n-type organic semiconductor layer / i-type organic semiconductor layer / p-type organic semiconductor layer (doped layer) / second electrode

[0326] As a specific layer structure of the vertical diode according to this embodiment, in which low-molecular-weight hydrophobic anions are attached to the surface of the first electrode, for example, the layer structures shown in (A6) to (A10) below are preferably exemplified. Note that although not described in (A6) to (A10) below, the first electrode or the second electrode is usually formed on a substrate.

[0327] (A6) First electrode / p-type organic semiconductor layer / second electrode (A7) First electrode / p-type organic semiconductor layer / n-type organic semiconductor layer / second electrode (A8) First electrode / p-type organic semiconductor layer / n-type organic semiconductor layer (doped layer) / second electrode (A9) First electrode / p-type organic semiconductor layer / i-type organic semiconductor layer / n-type organic semiconductor layer / second electrode (A10) First electrode / p-type organic semiconductor layer / i-type organic semiconductor layer / n-type organic semiconductor layer (doped layer) / second electrode

[0328] In (A1) to (A10), " / " means that the layers before and after it are adjacent to each other.

[0329] In (A1) to (A5), the term "p-type organic semiconductor layer (doped layer)" means that the p-type organic semiconductor layer is a doped layer containing holes and dopant anions, or that one of the outermost layers of the p-type organic semiconductor layer is a doped layer containing holes and dopant anions, and is adjacent to two electrodes.

[0330] In (A6) to (A10), the term "n-type organic semiconductor layer (doped layer)" means that the n-type organic semiconductor layer is a doped layer containing electrons and dopant cations, or that one of the outermost layers of the n-type organic semiconductor layer is a doped layer containing electrons and dopant cations, and is adjacent to two electrodes.

[0331] 3. Method for Manufacturing Vertical Diode A third embodiment of the present disclosure is a method for manufacturing a vertical diode in which a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode are adjacent to each other in this order, and the doped layer is stacked adjacent to the first electrode or the second electrode, the method including a doping step of forming the doped layer by bringing an aqueous solution containing a fourth oxidizing agent or a fourth reducing agent and a salt of a dopant ion (hereinafter, may be referred to as a "dope solution") into contact with a surface of an organic semiconductor layer precursor.

[0332] According to this embodiment, a doped layer into which carriers and dopant ions are injected is formed near the first electrode or the second electrode. This improves carrier injection from the electrode adjacent to the doped layer to the organic semiconductor layer, thereby obtaining a vertical diode exhibiting excellent rectification characteristics. Therefore, the manufacturing method according to this embodiment is useful as a method for manufacturing a rectifying diode. Furthermore, according to a preferred aspect of this embodiment, a vertical diode exhibiting excellent high-frequency response or a vertical diode exhibiting high current density even at a low voltage can be obtained.

[0333] [3-1. Doping Step] The doping step is a step of forming a doped layer as the outermost layer of the organic semiconductor layer, and is one step of a step of producing an organic semiconductor layer having a doped layer and an undoped layer (hereinafter, this step may be referred to as an "organic semiconductor layer production step"). In this embodiment, it is preferable that the organic semiconductor layer is composed of a doped layer and an undoped layer. Furthermore, the undoped layer may have a single-layer structure or a multi-layer structure.

[0334] The organic semiconductor layer preparation process is a process A in which an organic semiconductor layer precursor is subjected to a doping process to inject carriers and dopant ions into a region from the surface of the organic semiconductor layer precursor to a desired depth, thereby obtaining an organic semiconductor layer having a doped layer and an undoped layer; or a process B in which an organic semiconductor layer precursor is subjected to a doping process to inject carriers and dopant ions into the entire organic semiconductor layer precursor to form a doped layer, and an undoped organic semiconductor layer is laminated on the obtained doped layer, thereby obtaining an organic semiconductor layer.

[0335] The doping step in Step A is the same process as the doping step in the first embodiment, and preferred aspects thereof are also the same, so the explanation in the section [1-2. Doping step] is incorporated herein by reference. In this case, in the section [1-2. Doping step], the third oxidizing agent and the third reducing agent shall be read as the fourth oxidizing agent and the fourth reducing agent, respectively.

[0336] In step A, the region of the organic semiconductor layer precursor from the surface of the organic semiconductor layer precursor that has been in contact with the doping solution to the depth reached by the carriers and dopant ions usually becomes a doped layer, and the remaining region becomes an undoped layer. Note that the "desired depth" to which the carriers and dopant ions are injected is usually the thickness T of the doped layer described later. ｄ is equivalent to:

[0337] The doping step in step B is the same process as the doping step in the first embodiment, except that carriers and dopant ions are injected into the entire organic semiconductor layer precursor, not just a portion of it. Therefore, the explanation in the section [1-2. Doping step] is incorporated herein by reference, and the method for injecting carriers and dopant ions into the entire organic semiconductor layer precursor is as follows. Note that in the section [1-2. Doping step], the third oxidizing agent and the third reducing agent should be read as the fourth oxidizing agent and the fourth reducing agent, respectively.

[0338] Injection of carriers and dopant ions into the entire organic semiconductor layer precursor can be achieved by setting the thickness of the organic semiconductor layer precursor to a thickness corresponding to the doped layer, but can be more efficiently achieved by combining one or more of the following: adjusting the total content of the fourth oxidizing agent or the fourth reducing agent in the dope solution; adjusting the contact temperature between the organic semiconductor layer precursor and the dope solution; and adjusting the contact time between the organic semiconductor layer precursor and the dope solution. These conditions are preferably adjusted within the ranges described in [1-2. Doping step].

[0339] In step B, the organic semiconductor layer precursor and the undoped layer can be prepared by any method, such as a known method or a method similar thereto. Examples of known methods include the wet method described above in the section [1-2-4. Organic semiconductor layer precursor and organic semiconductor layer]. As described below, the organic semiconductor layer precursor is preferably prepared directly on the first electrode or the second electrode and then subjected to the doping step.

[0340] In the present disclosure, the "desired depth" to which carrier and dopant ions are implanted in step A is usually the thickness T of the doped layer described later.ｄ The thickness of the doped layer formed by the doping step in step B is usually equal to the thickness T ｄ is equivalent to

[0341] [3-2. Electrode Modification Step] When the doped layer is a layer adjacent to the second electrode, the manufacturing method according to this embodiment preferably includes an electrode modification step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with a surface modification liquid. The surface modification liquid used in the electrode modification step is any one of surface modification liquids (S1) to (S4). (S1) A surface modification liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation. (S4) A surface modification liquid containing a second oxidizing agent that oxidizes the first electrode and a low-molecular-weight hydrophobic closed-shell anion.

[0342] This step yields a surface-modified first electrode, in which low-molecular-weight hydrophobic ions generated from the first reducing agent or the first oxidizing agent are attached to the surface of the first electrode.

[0343] The electrode modification step in this embodiment is the same process as the electrode modification step in the first embodiment, and the preferred aspects are also the same. Therefore, the explanation in the section [1-1. Electrode modification step] is incorporated herein by reference.

[0344] When a doped layer is formed using a doping solution containing a fourth oxidant and a salt of a dopant anion in the doping step, a vertical diode having a doped layer in which holes and dopant anions are injected near the second electrode is obtained. Therefore, in the electrode modification step, it is preferable to use the surface modification solution (S1) or (S3) to prepare a first electrode into which electrons are injected and to which low-molecular-weight hydrophobic cations are electrostatically attached. This is because not only the hole injection property from the second electrode to the organic semiconductor layer but also the electron injection property from the first electrode to the organic semiconductor layer are improved, and the rectification characteristics and current density at low voltage of the vertical diode can be improved.

[0345] When a doped layer is formed using a doping solution containing a fourth reducing agent and a salt of a dopant cation in the doping step, a vertical diode having a doped layer in which electrons and dopant cations are injected near the second electrode is obtained. Therefore, in the electrode modification step, it is preferable to use the surface modification solution (S2) or (S4) to prepare a first electrode into which holes are injected and to which hydrophobic closed-shell anions are electrostatically attached. This is because not only the electron injection from the second electrode to the organic semiconductor layer but also the hole injection from the first electrode to the organic semiconductor layer is improved, and the rectification characteristics and current density at low voltage of the vertical diode can be improved.

[0346] [3-3. Lamination Step] In this embodiment, the first electrode, the organic semiconductor layer having a doped layer and an undoped layer, and the second electrode are laminated adjacent to each other in this order. At this time, the organic semiconductor layer and the first electrode or the second electrode are laminated so that the doped layer and the first electrode or the second electrode are in contact with each other. Furthermore, if the surface of the first electrode is modified in the electrode modification step, the first electrode and the organic semiconductor layer are laminated so that the modified surface of the first electrode and the organic semiconductor layer are in contact with each other.

[0347] The method for laminating each layer is not particularly limited as long as the layers are laminated in an order that satisfies the above-mentioned conditions, and any method such as a known method or a method similar thereto can be used.

[0348] For example, when the organic semiconductor layer preparation step is step A, lamination may be performed by preparing a first electrode, preparing an organic semiconductor layer precursor on the first electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a second electrode on the doped layer formed by the doping step, or by preparing a second electrode, preparing an organic semiconductor layer precursor on the second electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a first electrode on the doped layer formed by the doping step. Alternatively, each layer may be laminated by a transfer method in which an organic semiconductor layer is prepared on a transfer substrate by the organic semiconductor layer preparation step, this organic semiconductor layer is transferred onto one of the first electrode and the second electrode, and the other electrode is prepared on the organic semiconductor layer.

[0349] Furthermore, for example, when the organic semiconductor layer preparation step is step B, lamination may be performed by preparing a first electrode, preparing an organic semiconductor layer precursor on the first electrode, subjecting the organic semiconductor layer precursor to a doping step, preparing an undoped layer on the doped layer formed by the doping step, and preparing a second electrode on the undoped layer, or by preparing a second electrode, preparing an organic semiconductor layer precursor on the second electrode, subjecting the organic semiconductor layer precursor to a doping step, preparing an undoped layer on the doped layer formed by the doping step, and preparing a second electrode on the undoped layer. The organic semiconductor layer may be laminated on the first electrode and the second electrode by a transfer method, as described above. However, from the viewpoint of ensuring adhesion between the organic semiconductor layer and the first electrode or the second electrode, it is preferable to form an organic semiconductor layer precursor directly on the first electrode or the second electrode, and then subject the organic semiconductor layer precursor to a doping step, thereby laminating the organic semiconductor layer on the electrode.

[0350] Hereinafter, materials for the first electrode and the second electrode to be laminated together with the organic semiconductor layer, and a method for producing the first electrode and the second electrode will be described.

[0351] The first electrode and the second electrode are a pair of electrodes, i.e., when the first electrode is a cathode, the second electrode is an anode, and when the first electrode is an anode, the second electrode is a cathode.

[0352] In order to obtain good rectification characteristics in a vertical diode, it is generally desirable that the cathode have a work function smaller than the LUMO of the organic semiconductor constituting the adjacent organic semiconductor layer and smaller than the anode, and that the anode also have a work function larger than the LUMO of the organic semiconductor.

[0353] Therefore, it is preferable that the materials constituting the first electrode and the second electrode are appropriately selected from conductive materials depending on the work function of the paired electrode and the work function of the LUMO of the organic semiconductor. When the production method according to this embodiment includes an electrode modification step, the work function of the first electrode to be considered for selecting the electrode material is the work function of the first electrode after the first electrode surface modification.

[0354] Specific examples of materials constituting the first electrode and the second electrode include metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, molybdenum, and tungsten; alloys containing two or more of these metals; and metal oxides such as indium oxide, tin oxide, zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); with gold being preferred.

[0355] The first electrode and the second electrode are formed to a predetermined thickness by any known method or a method equivalent thereto, and are laminated together with other layers. Known methods for forming the first electrode and the second electrode include, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.

[0356] The thickness of the first electrode and the second electrode is not particularly limited and may be appropriately adjusted taking into consideration the application of the vertical diode, the element life, etc. Specific examples of the thickness of these electrodes include 10 nm or more and 200 nm or less, and preferably 20 nm or more and 50 nm or less.

[0357] When another layer is laminated on the first electrode, the first electrode is preferably formed on a substrate, and the same applies when another layer is laminated on the second electrode. The substrate is not particularly limited as long as it can form the first electrode or the second electrode, but it is preferably one that does not chemically react with the organic semiconductor that constitutes the organic semiconductor layer. Examples of such substrates include glass substrates and silicon substrates.

[0358] [3-4. Other Steps] The manufacturing method according to this embodiment may include other steps in addition to the steps described above. Examples of other steps include a step of washing the organic semiconductor layer after the doping step, and a step of washing the first electrode whose surface has been modified.

[0359] [4. Vertical Diode] A fourth embodiment of the present disclosure is a vertical diode in which a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode are stacked adjacent to each other in this order, with the doped layer being adjacent to the first electrode or the second electrode. The doped layer contains carriers and dopant ions, and the dopant ions are hydrophobic closed-shell ions. The vertical diode according to this embodiment can be manufactured by the manufacturing method according to the third embodiment. Furthermore, the vertical diode according to this embodiment has excellent rectification characteristics and can therefore be suitably used as a rectifying diode.

[0360] 5A and 5B , the vertical diode 20 according to this embodiment includes a first electrode 22, an organic semiconductor layer 24 having a doped layer 27 and an undoped layer 25, and a second electrode 28 stacked adjacent to each other in this order, with the doped layer 27 adjacent to the first electrode 22 or the second electrode 28. The doped layer 27 contains carriers (electrons or holes) and dopant ions. The dopant ions are preferably closed-shell ions, and more preferably hydrophobic closed-shell ions.

[0361] In this embodiment, the doped layer is a layer formed by the doping step in the third embodiment. The dopant ions contained in the doped layer are derived from salts of dopant ions contained in the doping solution and have the opposite polarity to the carriers. In the vertical diode according to this embodiment, holes and dopant anions are injected into the doped layer adjacent to one electrode, thereby improving hole injection from the electrode adjacent to the doped layer to the organic semiconductor layer. Furthermore, electrons and dopant cations are injected into the doped layer adjacent to one electrode, thereby improving electron injection from the electrode adjacent to the doped layer to the organic semiconductor layer.

[0362] The vertical diode according to this embodiment exhibits excellent rectification characteristics due to the formation of such a doped layer near one of the electrodes. Furthermore, according to a preferred aspect of this embodiment, a vertical diode having excellent high-frequency response or a vertical diode exhibiting high current density even at low voltage can be obtained. Therefore, the vertical diode according to this embodiment is considered to be applicable to various devices having a diode structure, such as solar cells and light-emitting diodes, and is also expected to be used in wireless communication electronic tags and other devices that require high-frequency response.

[0363] It is preferable that the dopant ions contained in the doped layer do not form salts with counter ions, and it is more preferable that the dopant ions do not form salts with any counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, and ions of the metal contained in the second electrode.

[0364] More specifically, among the dopant ions contained in the doped layer, the proportion of dopant ions that form salts with counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, or ions of the metal contained in the second electrode is preferably 0 mol% or more and 25 mol% or less, more preferably more than 0 mol% and 20 mol% or less, even more preferably 0 mol% or more and 15 mol% or less, and particularly preferably 5 mol% or more and 10 mol% or less.

[0365] The proportion of dopant ions that form salts with counter ions can be measured by X-ray photoelectron spectroscopy (XPS).

[0366] When a hole-transporting organic semiconductor layer, i.e., a p-type organic semiconductor layer, is used as the organic semiconductor constituting the doped layer, holes and dopant anions are injected into the doped layer, thereby providing a vertical diode with excellent rectification characteristics and high current density at low voltage. On the other hand, when an electron-transporting organic semiconductor layer, i.e., an n-type organic semiconductor layer, is used as the organic semiconductor constituting the doped layer, electrons and dopant cations are injected into the doped layer, thereby providing a vertical diode with excellent rectification characteristics and high current density at low voltage.

[0367] Furthermore, the organic semiconductor constituting the doped layer is preferably the same compound as the organic semiconductor constituting the undoped layer, because when the doped layer and the undoped layer are made of the same organic semiconductor, carrier injection from the doped layer to the undoped layer can be improved.

[0368] Doped layer thickness T ｄ is not particularly limited, but is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more and 20 nm or less, even more preferably 3 nm or more and 15 nm or less, and even more preferably 4 nm or more and 10 nm or less. ｄ The total thickness of the organic semiconductor layer T ｏ The thickness of the undoped layer T subtracted from ｕ is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 50 nm or less, even more preferably 12 nm or more and 30 nm or less, and even more preferably 15 nm or more and 25 nm or less. ｄ By setting the value of the current flowing in the forward direction to be within the above range, it is possible to increase the value of the current flowing in the forward direction while maintaining rectification.

[0369] Undoped layer T ｕ The thickness of the undoped layer T can be estimated by capacitance measurement, and the thickness of the undoped layer T can be estimated by contact step height measurement. ｕ If the thickness of the doped layer can be determined, the thickness of the doped layer can also be estimated.

[0370] The undoped layer is a layer into which carriers and dopant ions are not implanted during the doping process in the third embodiment. However, since dopant ions in the doped layer may diffuse into the region during the manufacturing process after the doping process and during storage of the vertical diode, in this disclosure, the layer that acts as a resistive component in capacitance measurement is referred to as the "doped layer" and the layer that acts as a capacitive component is referred to as the "undoped layer." Furthermore, although the undoped layer 25 is illustrated as a single layer in Figures 5(A) to 5(C), the undoped layer may have a multilayer structure.

[0371] As shown in FIG. 5C, in the vertical diode 20 according to this embodiment, when the doped layer 27 is a layer adjacent to the second electrode 28, it is preferable that the low-molecular-weight hydrophobic ions 23 are attached to the surface of the first electrode that is adjacent to the organic semiconductor layer 24.

[0372] In this embodiment, the low-molecular-weight hydrophobic ions are ions that electrostatically attach to the surface of the first electrode adjacent to the organic semiconductor layer by the electrode modification step in the third embodiment. The types of low-molecular-weight hydrophobic ions, the coverage rate of the low-molecular-weight hydrophobic ions, and the proportion of the low-molecular-weight hydrophobic ions that form salts with counterions in this embodiment are the same as those of the low-molecular-weight hydrophobic ions attached to the first electrode in the first embodiment, including preferred embodiments thereof. Therefore, the descriptions of the types of low-molecular-weight hydrophobic ions, the coverage rate of the low-molecular-weight hydrophobic ions, and the proportion of the low-molecular-weight hydrophobic ions that form salts with counterions in the section [2. Vertical Diode] are incorporated herein by reference.

[0373] When the vertical diode has a doped layer adjacent to the second electrode, and the doped layer is a layer into which holes and dopant anions are injected, it is preferable that the low-molecular-weight hydrophobic ions electrostatically attached to the surface of the first electrode are low-molecular-weight hydrophobic cations, i.e., electrons have been injected into the first electrode by an electrode modification process. This improves hole injection from the second electrode to the organic semiconductor layer and electron injection from the first electrode to the organic semiconductor layer, thereby facilitating forward current (current flowing from the second electrode to the first electrode), significantly improving rectification characteristics and current density at low voltages. In this case, it is more preferable that the layer of the organic semiconductor layer adjacent to the first electrode is an n-type organic semiconductor layer.

[0374] On the other hand, when the vertical diode has a doped layer adjacent to the second electrode, and the doped layer is a layer into which electrons and dopant cations are injected, it is preferable that the low-molecular-weight hydrophobic ions electrostatically attached to the surface of the first electrode are low-molecular-weight hydrophobic anions, i.e., holes have been injected into the first electrode by the electrode modification process. This improves the electron injection from the second electrode to the organic semiconductor layer and the hole injection from the first electrode to the organic semiconductor layer, thereby facilitating the flow of forward current (current flowing from the first electrode to the second electrode), significantly improving the rectification characteristics and current density at low voltage. In this case, it is more preferable that the layer of the organic semiconductor layer adjacent to the first electrode is a p-type organic semiconductor layer.

[0375] Specific examples of the layer structure of the vertical diode according to this embodiment include the layer structures shown in (B1) to (B12) below. Although not described in (B1) to (B12) below, the first electrode or the second electrode is usually formed on a substrate.

[0376] (B1) First electrode / (doped layer) n-type organic semiconductor layer / second electrode (B2) First electrode / (doped layer) n-type organic semiconductor layer / p-type organic semiconductor layer / second electrode (B3) First electrode / (doped layer) n-type organic semiconductor layer / i-type organic semiconductor layer / p-type organic semiconductor layer (doped region) / second electrode (B4) First electrode / (doped layer) p-type organic semiconductor layer / second electrode (B5) First electrode / (doped layer) p-type organic semiconductor layer / n-type organic semiconductor layer / second electrode (B6) First electrode / (doped layer) p-type organic semiconductor layer / i-type organic semiconductor layer / n-type organic semiconductor layer / second electrode (B7) First electrode / n-type organic semiconductor layer (doped layer) / second electrode (B8) First electrode / p-type organic semiconductor layer / n-type organic semiconductor layer (doped layer) / second electrode (B9) First electrode / p-type organic semiconductor layer / i-type organic semiconductor layer / n-type organic semiconductor layer (doped layer) / second electrode (B10) First electrode / p-type organic semiconductor layer (doped layer) / second electrode (B11) First electrode / n-type organic semiconductor layer / p-type organic semiconductor layer (doped layer) / second electrode (B12) First electrode / n-type organic semiconductor layer / i-type organic semiconductor layer / p-type organic semiconductor layer (doped layer) / second electrode

[0377] In (B1) to (B12), " / " means that the layers before and after it are adjacent to each other.

[0378] In (B1) to (B3), the term "(doped layer) n-type organic semiconductor layer" means that a doped layer into which electrons and dopant cations are injected is disposed at a position of the n-type organic semiconductor layer adjacent to the first electrode, or that the entire n-type organic semiconductor layer is a doped layer into which electrons and dopant cations are injected.

[0379] In (B4) to (B6), the term "(doped layer) p-type organic semiconductor layer" means that a doped layer into which holes and dopant anions are injected is disposed at a position of the p-type organic semiconductor layer adjacent to the first electrode, or that the entire p-type organic semiconductor layer is a doped layer into which holes and dopant anions are injected.

[0380] In (B7) to (B9), the term "n-type organic semiconductor layer (doped layer)" means that a doped layer into which electrons and dopant cations are injected is disposed at a position of the n-type organic semiconductor layer adjacent to the second electrode, or that the entire n-type organic semiconductor layer is a doped layer into which electrons and dopant cations are injected.

[0381] In (B10) to (B12), the term "p-type organic semiconductor layer (doped layer)" means that a doped layer into which holes and dopant anions are injected is disposed at a position of the p-type organic semiconductor layer adjacent to the second electrode, or that the entire p-type organic semiconductor layer is a doped layer into which holes and dopant anions are injected.

[0382] In the case of (B8) and (B9), it is also preferable that a low-molecular-weight hydrophobic anion is attached to the surface of the first electrode that is adjacent to the p-type organic semiconductor layer.In the case of (B11) and (B12), it is also preferable that a low-molecular-weight hydrophobic cation is attached to the surface of the first electrode that is adjacent to the n-type organic semiconductor layer.

[0383] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples without departing from the gist of the disclosure. Unless otherwise specified, the solution processes for electrode modification and doping in the following examples were carried out in an air atmosphere.

[0384] [Reagents] The reducing agents and organic semiconductors used in the examples and comparative examples are shown below.

[0385]

[0386]

[0387] Example 1 A vertical diode having a layer structure of surface-modified Au electrode / P(NDI-2T) / Au electrode was fabricated by the following procedure. The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0388] (1) Au electrodes were obtained by forming a gold film on a glass substrate using resistance heating deposition. (2) The gold electrode was immersed in an aqueous solution containing 1 mM TPPA-OH, 1 M fructose, and 50 mM riboflavin. (3) The gold electrode was washed with pure water to obtain a surface-modified gold electrode. (4) A solution containing 1 wt% N2200 (P(NDI-2T)) was spin-coated onto the surface-modified gold electrode at 2,000 rpm for 60 seconds. (5) The coating was baked at 80°C for 20 minutes to form an organic semiconductor layer approximately 70 nm thick. (6) A gold top electrode (30 nm) was deposited on the organic semiconductor layer to obtain a vertical diode.

[0389] Example 2 A Cu electrode with a surface modification was prepared by the following procedure.

[0390] (1) A Cu film was formed on a glass substrate by vacuum resistance heating deposition to obtain a Cu electrode. (2) BQ (20 mM), Li-TFPB (5 mM), and H ２ SO ４ The Cu electrode was immersed in an aqueous solution containing (1 mM) for 30 seconds. (3) The Cu electrode was washed with pure water and dried by nitrogen blowing to obtain a surface-modified Cu electrode.

[0391] The surface-modified Cu electrode was subjected to ultraviolet photoelectron spectroscopy (UPS) using a 21.2 eV helium light source. The UPS measurement results for the surface-modified Cu electrode are shown in Figure 10(A). An enlarged view of the high-binding-energy region is shown in Figure 10(B). Based on the rise position and the light source energy (21.2 eV), the surface-modified Cu electrode was evaluated to have a work function of 5.12 eV.

[0392] Comparative Example 1 An unmodified Cu electrode was obtained by the procedure (1) of Example 2. Ultraviolet photoelectron spectroscopy (UPS) measurement was performed on the unmodified Cu electrode using a 21.2 eV helium light source. The UPS measurement results for the unmodified Cu electrode are shown in Figure 11(A). An enlarged view of the high binding energy region is shown in Figure 11(B). Based on the rise position and the light source energy (21.2 eV), the unmodified Cu electrode was evaluated to have a work function of 4.66 eV.

[0393] [Example 3] Using an Au electrode whose surface had been modified under the same conditions as in Example 2 as the first electrode, a vertical diode having a layer structure of surface-modified Au electrode / PTAA / Au electrode was fabricated by the following procedure. The current-voltage characteristics of the obtained vertical diode are shown in Figure 12.

[0394] (1) PTAA was dissolved in o-dichlorobenzene to prepare a 2 wt % PTAA solution. This solution was spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds. (2) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer. (3) Au was deposited on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.

[0395] A vertical diode having a layer structure of a surface-modified Cu electrode / PTAA / Au electrode was fabricated in the same manner as in Example 3, except that the surface-modified Cu electrode fabricated in Example 2 was used as the first electrode. The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0396] [Example 5] A vertical diode having a layer structure of a surface-modified Cu electrode / PTAA / Cu electrode was fabricated in the same manner as in Example 4, except that in (3), Cu was deposited by vacuum resistance heating deposition. The current-voltage characteristics of the obtained vertical diode are shown in Figure 14.

[0397] Example 6 A vertical diode having a layer structure of a surface-modified Au bilayer electrode / P(NDI-2T) / Au electrode was fabricated by the following procedure. The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0398] (1) Cr 2 nm and Au 20 nm were sequentially laminated on a glass substrate by vacuum resistance heating deposition to obtain an Au double-layer electrode. (2) The glass substrate on which the Au double-layer electrode was formed was exposed to UV / O for 15 minutes. ３ (3) UV / O ３ The treated glass substrate was washed in acetone and isopropanol for 10 minutes each using an ultrasonic cleaner, and then dried on a hot plate at 100°C for 10 minutes. (4) (RuMes*Cp) ２A 2 mM butyl acetate solution of NDI-2T was dropped onto the Au bilayer electrode and allowed to stand for 10 seconds. (5) The glass substrate was spun at 2,000 rpm for 20 seconds using a spin coater. (6) The coating was dried on a hot plate at 80°C for 5 minutes. (7) Butyl acetate solvent was dropped onto the Au bilayer electrode, and the glass substrate was spun at 2,000 rpm for 20 seconds using a spin coater to clean the surface of the Au bilayer electrode. (8) The surface-modified electrode was obtained by drying on a hot plate at 80°C for 5 minutes. (9) P(NDI-2T) was dissolved in o-dichlorobenzene to obtain a 1 wt% P(NDI-2T) solution. The resulting solution was spin-coated on the surface-modified electrode at 2,000 rpm for 60 seconds. (10) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer approximately 70 nm thick. (11) A 30 nm thick Au film was formed on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.

[0399] [Evaluation of AC to DC Conversion Efficiency] Figure 8 shows a graph plotting the AC power introduced into the vertical diode on the horizontal axis and the AC to DC conversion efficiency. In Figure 8, the resistance values ​​are the set values ​​of the variable resistors. Figure 8 shows that the vertical diode obtained in Example 13 converted 1 GHz AC power with an efficiency of about 9%. This efficiency is more than one order of magnitude higher than the reported value for solution-processed diodes.

[0400] [Example 7] In (5), (RuMes*Cp) ２ CoCp ２ A vertical diode having a layer structure of a surface-modified Au bilayer electrode / P(NDI-2T) / Au electrode was fabricated in the same manner as in Example 6, except for changing the electrode structure to the following: The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0401] Comparative Example 2 A vertical diode having a layer structure of an unmodified Au bilayer electrode / P(NDI-2T) / Au electrode was fabricated in the same manner as in Example 6, except that steps (4) to (8) were not performed. The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0402] [Evaluation of Coverage of Small-Molecular-Weight Hydrophobic Ions] XPS elemental analysis was performed on the unmodified Au bilayer electrode obtained in Comparative Example 2 and the surface-modified Au bilayer electrode obtained in Example 6. The results are shown in Figure 18. A slight C1s peak due to carbon debris was also observed in the unmodified Au bilayer electrode. The intensities of C1s and Ru3d were stronger in the surface-modified Au bilayer electrode. The density of Ru complex molecular cations deposited on the Au bilayer electrode surface was determined from the intensities of Ru3d and Au3d. It was found that the thickness of the Ru complex molecular cation layer was less than a monolayer (less than 1 nm), covering approximately 30% by area of ​​the Au bilayer electrode.

[0403] Example 8: (RuMes*Cp) was prepared by the following procedure. ２ An ITO electrode was fabricated whose surface was modified with a low-molecular-weight hydrophobic closed-shell cation derived from the compound. The resulting surface-modified ITO electrode was subjected to photoelectron yield spectroscopy (PYS) measurement. The results are shown in FIG. 19 and Table 1.

[0404] (1) 5 minutes of UV / O ３ The surface of the ITO electrode was cleaned by the treatment. (2) (RuMes*Cp) ２ A 2 mM butyl acetate solution was irradiated with UV / ３ The solution was dropped onto the treated ITO electrode, allowed to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds. (3) The coating was dried on a hot plate at 80°C for 5 minutes. (4) Butyl acetate was dropped onto the ITO electrode, and the ITO electrode surface was cleaned by rotating at 3,000 rpm for 60 seconds. (5) The cleaned ITO electrode was dried on a hot plate at 80°C for 5 minutes to obtain a surface-modified ITO electrode.

[0405] Comparative Example 3 An unmodified ITO electrode was prepared according to the procedure (1) of Example 8.

[0406] Comparative Example 4 An ITO electrode whose surface was modified with PEI was prepared by the following procedure. The obtained surface-modified ITO electrode was subjected to photoelectron yield spectroscopy (PYS) measurement. The results are shown in FIG. 21 and Table 1.

[0407] (1) 5 minutes of UV / O ３The ITO electrode surface was cleaned by this treatment. (2) A 0.2 wt% PEI aqueous solution prepared by dissolving PEI in pure water was dropped onto the ITO electrode, allowed to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds. (3) The coating was dried on a hot plate at 90°C for 30 minutes. (4) Butyl acetate was dropped onto the ITO electrode, and the ITO electrode surface was cleaned by spinning at 3,000 rpm for 60 seconds. (5) The cleaned ITO electrode was dried on a hot plate at 80°C for 5 minutes to obtain a surface-modified ITO electrode.

[0408] [Evaluation of Work Function] Photoelectron yield spectroscopy (PYS) measurements were performed on the surface-modified ITO electrode obtained in Example 8, the unmodified ITO electrode obtained in Comparative Example 3, and the surface-modified ITO electrode obtained in Comparative Example 4. The measurement results for Example 8, Comparative Example 3, and Comparative Example 4 are shown in Figures 19 to 21, respectively. The calculated work functions are also shown in Table 1.

[0409]

[0410] [Surface Composition Analysis] XPS elemental analysis was performed on the surface-modified ITO electrode obtained in Example 8 and the unmodified ITO electrode obtained in Comparative Example 3. The results are shown in FIG. 22 and Table 2. As shown in FIG. 22, the surface-modified ITO electrode obtained in Example 8 contained (RuCp*Mes) on the surface of the ITO electrode. ２ It can be seen that a layer of low molecular weight hydrophobic closed-shell cations derived from the cations is formed.

[0411]

[0412] [Evaluation of Layer Thickness of Low-Molecular-Weight Hydrophobic Closed-Shell Cation Layer] A simulation was performed to determine the elemental structure when a monolayer of cations was deposited on the surface of an ITO electrode. The simulation results are shown in Table 3.

[0413]

[0414] The Ru composition ratio determined by XPS measurement of the surface-modified ITO electrode obtained in Example 8 was 1 / 10 of that in the monolayer deposition model. Therefore, in Example 8, (RuCp*Mes) ２It can be seen that the thickness of the layer of the resulting low-molecular-weight hydrophobic closed-shell cations is less than a monolayer (1 nm or less). In Example 8, electron injection and deposition of low-molecular-weight hydrophobic closed-shell cations occur due to the redox reaction, which is thought to result in a shift in the electric field and vacuum level, resulting in a decrease in the work function of the surface-modified ITO electrode.

[0415] Example 9 A vertical diode having a layer structure of a surface-modified ITO electrode / P(NDI-2T) / Au electrode was fabricated by the following procedure.

[0416] (1) 5 minutes of UV / O ３ The surface of the ITO electrode was cleaned by the treatment. (2) (RuMes*Cp) ２ A 2 mM butyl acetate solution was irradiated with UV / ３ The solution was dropped onto the treated ITO, allowed to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds. (3) The coating was dried on a hot plate at 80°C for 5 minutes. (4) Butyl acetate was dropped onto the ITO electrode, and the ITO electrode surface was cleaned by rotating at 3,000 rpm for 60 seconds. (5) The cleaned ITO electrode was dried on a hot plate at 80°C for 5 minutes to obtain a surface-modified ITO electrode. (6) A 1 wt% P(NDI-2T) solution prepared by dissolving P(NDI-2T) in o-dichlorobenzene was spin-coated onto the surface-modified ITO electrode at 2,000 rpm for 60 seconds. (7) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer approximately 70 nm thick. (8) A 40 nm thick Au film was deposited on the organic semiconductor layer under high vacuum conditions using a vacuum resistance heating deposition machine, thereby obtaining a vertical diode.

[0417] Comparative Example 5 A vertical diode was fabricated by the following procedure.

[0418] (1) 5 minutes of UV / O ３The ITO electrode surface was cleaned by this process, yielding an unmodified ITO electrode. (2) A 1 wt% P(NDI-2T) solution prepared by dissolving P(NDI-2T) in o-dichlorobenzene was spin-coated onto the ITO electrode at 2,000 rpm for 60 seconds. (3) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer. (4) A 40 nm thick Au layer was deposited on the organic semiconductor layer under high vacuum conditions using a vacuum resistance heating deposition machine, yielding a vertical diode.

[0419] [Evaluation of Coverage Rate of Small-Molecular-Weight Hydrophobic Ions] XPS elemental analysis was performed on the surface-modified ITO electrode obtained in Example 9 and the unmodified ITO electrode obtained in Comparative Example 5. The measurement results of Example 9 and Comparative Example 5 are shown in Fig. 23 and Fig. 24, respectively.

[0420] Surface modification resulted in an increase in C1s and Ru3d, (RuMes*Cp). ２ The results showed that cations derived from Ru3d were deposited on the surface of the ITO electrode (see FIG. 23). Furthermore, a comparison of the Ru3d intensity and the intensity derived from ITO showed that the coverage of the low-molecular-weight hydrophobic ions on the surface-modified ITO electrode obtained in Example 8 was approximately 30 area %.

[0421] Example 10 A vertical diode having a layer structure of a surface-modified ITO electrode / P(NDI-2T) / Au electrode was fabricated by the following procedure.

[0422] (1) 5 minutes of UV / O ３ The surface of the ITO electrode was cleaned by the treatment. (2) (RuMes*Cp) ２ A 2 mM butyl acetate solution was irradiated with UV / ３The solution was dropped onto the treated ITO electrode, allowed to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds. (3) The coating was dried on a hot plate at 80°C for 5 minutes. (4) Butyl acetate was dropped onto the ITO electrode, and the ITO electrode surface was cleaned by rotating at 3,000 rpm for 60 seconds. (5) The cleaned ITO electrode was dried on a hot plate at 80°C for 5 minutes to obtain a surface-modified ITO electrode. (6) A 1 wt% P(NDI-2T) solution prepared by dissolving P(NDI-2T) in o-dichlorobenzene was spin-coated onto the surface-modified ITO substrate at 2,000 rpm for 60 seconds. (7) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer approximately 70 nm thick. (8) A 40 nm thick Au film was deposited on the organic semiconductor layer under high vacuum conditions using a vacuum resistance heating deposition machine, thereby obtaining a vertical diode.

[0423] Comparative Example 6 A vertical diode having a layer structure of unmodified ITO electrode / P(NDI-2T) / Au electrode was fabricated in the same manner as in Example 10, except that steps (2) to (5) were not performed.

[0424] [Evaluation of Rectification Ratio] The current-voltage characteristics of the vertical diode obtained in Example 10 and the vertical diode obtained in Comparative Example 6 are shown in Figures 25 and 26, respectively. The forward current, reverse current, and rectification ratio of these vertical diodes are also shown in Table 4. Table 4 shows that the electron injection characteristics from the ITO electrode to the organic semiconductor layer were improved by the surface modification.

[0425]

[0426] Example 11 A vertical diode having a layer structure of a surface-modified Au electrode / PTAA (doped layer) / Au electrode was fabricated by the following procedure.

[0427] (1) Au electrode is UV / O ３(2) The Au electrode was immersed in an aqueous solution containing hydroquinone HQ (1 mM) and 1,3-dimethylimidazolium hydroxide (0.1 mM) for 30 seconds and then dried with nitrogen blow to obtain a surface-modified Au electrode. (3) PTAA was dissolved in o-dichlorobenzene to prepare a 2 wt% PTAA solution. This solution was spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds. (4) The coating was dried on a hot plate at 80°C for 20 minutes to form an organic semiconductor layer. (5) To dope holes near the surface of the organic semiconductor layer, the organic semiconductor layer formed on the Au electrode was immersed in an aqueous solution containing sulfuric acid (1 mM), benzoquinone (10 mM), and lithium tetrakis(pentafluorophenyl)borate (10 mM) for 30 seconds, and then rinsed with pure water. (6) Au electrodes were formed on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.

[0428] Example 12 A vertical diode having a layer structure of a surface-modified Au electrode / PTAA / Au electrode was fabricated in the same manner as in Example 11, except that (5) was not carried out.

[0429] [Evaluation of Rectification Ratio] The current-voltage characteristics of the vertical diode obtained in Example 11 and the vertical diode obtained in Example 12 are shown in Figures 27 and 28, respectively. From Figures 27 and 28, it can be seen that in Example 11, in which a doped layer was formed near the Au electrode, the reverse current was suppressed and the rectification ratio was higher than in Example 12. Furthermore, the vertical diodes obtained in Examples 11 and 12 had a current density of 100 A cm at a voltage of 3 V. －２ It can be seen that a high current density is achieved even at a low voltage.

[0430] Example 13 A vertical diode having a layer structure of a surface-modified Au bilayer electrode / P(NDI-2T) / Au electrode was fabricated in the same manner as in Example 6, except that in (9), the P(NDI-2T) concentration in the P(NDI-2T) solution was changed to 0.5 wt %. The thickness of the P(NDI-2T) layer of this vertical diode was 25 nm. The current-voltage characteristics of the obtained vertical diode are shown in FIG.

[0431] The vertical diode obtained in Example 13 had an organic semiconductor layer as thin as 25 nm, but as can be seen from FIG. 29, it had excellent rectification characteristics and a high current density at low voltage.

[0432] Evaluation of 10% rectification at 1 GHz: Evaluation of 10% rectification at 1 GHz was performed using the circuit shown in Figure 6. A 1 GHz AC signal generated by a signal generator (waveform generator) was amplified by an amplifier, and this AC power was evaluated as P1 using a power meter. Note that the component of the power that was reflected without being introduced into the diode was measured as P2 using the power meter.

[0433] When AC power is introduced into the vertical diode, it is rectified and converted into DC power. This DC power is then introduced into a variable resistor connected by a bias tee. The resistance value of this variable resistor and the voltage V generated across both ends are ３ The magnitude of the DC power converted by the vertical diode was evaluated from the voltage V ３ The results are shown in Figure 7.

[0434] [Evaluation of AC to DC conversion efficiency] Figure 30 shows a graph plotting the resistance of the variable resistor when 70 mW or 42 mW of AC power is introduced into the vertical diode against the conversion efficiency from AC to DC on the horizontal axis. Figure 30 shows that the vertical diode obtained in Example 13 converted 1 GHz AC power with an efficiency of about 8%. This efficiency is more than one order of magnitude higher than the reported value for solution-processed diodes.

[0435] Example 14 (1) A gold film was formed on a glass substrate by resistance heating deposition, and an Au electrode was obtained by photolithographic patterning. (2) The Au electrode was immersed in an aqueous solution containing 0.25 mM TPPA-OH, 1 M fructose, and 10 mM riboflavin. (3) The Au electrode was rinsed with pure water to obtain a surface-modified Au electrode. (4) A solution containing 0.8 wt% N2200 (P(NDI-2T)) was spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds. (5) The coating was baked at 80°C for 20 minutes to form an organic semiconductor layer approximately 40 nm thick. (6) A 30 nm Au top electrode was vapor-deposited on the organic semiconductor layer, and the Au top electrode was patterned using photolithography to obtain a vertical diode.

[0436] [Evaluation of Rectification Ratio] The current-voltage characteristics of the vertical diode obtained in Example 14 are shown in Figure 31. Figure 31 shows that a high rectification ratio and a high current value suitable for a rectifying diode can be achieved even when the electrode surface is modified in an air atmosphere.

Claims

1. A vertical diode having a first electrode, an organic semiconductor layer, and a second electrode stacked adjacent to each other in this order, wherein low molecular weight hydrophobic ions are attached to a surface of the first electrode adjacent to the organic semiconductor layer.

2. The vertical diode of claim 1, wherein the small molecule hydrophobic ion is a small molecule hydrophobic closed shell ion.

3. The vertical diode according to claim 1, wherein the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic cation, and the low-molecular-weight hydrophobic cation is one or more selected from the group consisting of cations represented by formulas (1A) to (1F). (wherein M1 is rhodium or iridium; M2 is ruthenium; M3 is cobalt; R １ ~R ６ are each independently a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent.

4. The vertical diode according to claim 1, wherein the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic anion, and the low-molecular-weight hydrophobic anion is one or more types selected from the group consisting of anions represented by formulas (3F) to (3G): (In the formula, R １４ are each independently a hydrogen atom, a halogen atom, or a fluorinated alkyl group which may have a substituent; R １５ are each independently a perfluoroalkyl group, and two R １５ may be linked to each other to form a ring.) 5. The vertical diode according to claim 1, wherein the low-molecular-weight hydrophobic ions are attached to 10% by area or more and 50% by area or less of the surface of the first electrode adjacent to the organic semiconductor layer.

6. The vertical diode according to claim 1, wherein the small molecule hydrophobic ions form an ionic layer on a surface of the first electrode adjacent to the organic semiconductor layer, and the thickness of the ionic layer is 2 nm or less or a thickness of three molecular layers or less.

7. The vertical diode according to claim 1, wherein the ratio of the low-molecular-weight hydrophobic ions forming a salt with a counter ion among the low-molecular-weight hydrophobic ions attached to the surface of the first electrode adjacent to the organic semiconductor layer is 25 mol % or less, and the counter ions are counter ions other than ions derived from an organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, and ions of a metal contained in the first electrode.

8. The vertical diode of claim 1, wherein said first electrode is a copper electrode.

9. The vertical diode according to claim 1, wherein the small molecule hydrophobic ions are small molecule hydrophobic cations, the organic semiconductor layer has a doped layer and an undoped layer, and the doped layer is a layer adjacent to the second electrode and contains holes and dopant anions.

10. The vertical diode of claim 1, wherein the small molecule hydrophobic ion is a small molecule hydrophobic anion, the organic semiconductor layer has a doped layer and an undoped layer, and the doped layer is adjacent to the second electrode and contains electrons and dopant cations.

11. The vertical diode according to claim 1, wherein the organic semiconductor layer has a thickness of 15 nm or more and 50 nm or less.

12. The vertical diode according to claim 1, having a conversion efficiency from AC power at a frequency of 10 MHz to DC power of more than 5%.

13. The vertical diode according to claim 1, having a conversion efficiency from AC power at a frequency of 1 GHz to DC power of more than 5%.

14. A method for manufacturing a vertical diode having a first electrode, an organic semiconductor layer, and a second electrode stacked adjacent to each other in this order, comprising: an electrode modification step of contacting a surface of the first electrode with a surface modification liquid to obtain a surface-modified first electrode; and a lamination step of laminating the first electrode and the organic semiconductor layer so that the surface of the first electrode modified in the electrode modification step comes into contact with the organic semiconductor layer, wherein the surface modification liquid is any one of the following surface modification liquids (S1) to (S4): (S1) A surface modification liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation. (S4) A surface modification liquid containing a second oxidizing agent that oxidizes the first electrode and a low-molecular-weight hydrophobic closed-shell anion.

15. The method for producing a vertical diode according to claim 14, wherein the surface modification liquid (S1) further contains a low molecular weight hydrophobic cation different from the low molecular weight hydrophobic cation resulting from the first reducing agent.

16. The method for producing a vertical diode according to claim 14, wherein the surface modification liquid (S2) further comprises a low-molecular-weight hydrophobic anion different from the low-molecular-weight hydrophobic anion resulting from the first oxidizing agent.

17. The method for producing a vertical diode according to claim 14, wherein the surface modifying liquid is the surface modifying liquid (S1) or the surface modifying liquid (S2).

18. The method for producing a vertical diode according to claim 14, wherein the surface modifying liquid is the surface modifying liquid (S3) or the surface modifying liquid (S4).

19. The method for producing a vertical diode according to claim 14, wherein the solvent of the surface modification liquid is water, and the electrode modification step is carried out in an air atmosphere.

20. A method for producing a vertical diode according to claim 14, wherein the organic semiconductor layer is an organic semiconductor layer having a doped layer and an undoped layer, and the doped layer is a layer adjacent to the second electrode, and further comprising: a doping step of forming the doped layer by contacting a surface of an organic semiconductor layer precursor with an aqueous solution containing one or more selected from the group consisting of a third oxidizing agent and a third reducing agent and a salt of a dopant ion; and a lamination step of laminating the organic semiconductor layer and the second electrode so that the doped layer and the second electrode are in contact with each other.

21. The method for producing a vertical diode according to claim 20, wherein the third reducing agent is one or more selected from the group consisting of a hydroquinone compound having a hydroquinone skeleton and a reduced coenzyme, and the third oxidizing agent is a quinone compound having a quinone skeleton.

22. A surface modification liquid for modifying the surface of an electrode and changing the work function of the electrode, the surface modification liquid being any one of the following surface modification liquids (S1) to (S4): (S1) A surface modification liquid containing a first reducing agent that reduces the electrode and generates a low molecular weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent that oxidizes the electrode and generates a low molecular weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent that reduces the electrode and a low molecular weight hydrophobic closed shell cation. (S4) A surface modification liquid containing a second oxidizing agent that oxidizes the electrode and a low molecular weight hydrophobic closed shell anion.

23. The surface modification liquid according to claim 22, wherein the surface modification liquid (S1) further comprises a low molecular weight hydrophobic cation different from the low molecular weight hydrophobic cation resulting from the first reducing agent.

24. The surface modification liquid according to claim 22, wherein the surface modification liquid (S2) further comprises a small molecule hydrophobic anion different from the small molecule hydrophobic anion resulting from the first oxidizing agent.

25. The surface modifying liquid according to claim 22, wherein the surface modifying liquid is the surface modifying liquid (S1) or the surface modifying liquid (S2).

26. The surface modifying liquid according to claim 22, wherein the surface modifying liquid is the surface modifying liquid (S3) or the surface modifying liquid (S4).

27. The surface modification liquid of claim 22, wherein the solvent of the surface modification liquid is water.

28. A vertical diode comprising a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode stacked adjacent to each other in this order, with the doped layer adjacent to the first electrode or the second electrode, wherein the doped layer contains carriers and dopant ions, and the dopant ions are hydrophobic closed shell ions.

29. The vertical diode of claim 28, wherein the doped layer is a layer adjacent to the second electrode, the carriers are holes, the dopant ions are hydrophobic closed shell anions, and small molecule hydrophobic closed shell cations are attached to a surface of the first electrode adjacent to the organic semiconductor layer.

30. The vertical diode of claim 28, wherein the doped layer is a layer adjacent to the second electrode, the carriers are electrons, the dopant ions are hydrophobic closed shell cations, and a small molecule hydrophobic closed shell anion is attached to a surface of the first electrode adjacent to the organic semiconductor layer.

31. The vertical diode according to claim 28, wherein the ratio of the dopant ions forming salts with counter ions among the dopant ions contained in the doped layer is 25 mol % or less, and the counter ions are ions derived from an organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of a metal contained in the first electrode, and ions of a metal contained in the second electrode.

32. The vertical diode according to claim 28, wherein the organic semiconductor constituting the doped layer is the same compound as the organic semiconductor constituting the undoped layer.

33. The vertical diode according to claim 28, wherein the organic semiconductor layer has a thickness of 15 nm or more and 50 nm or less.

34. A method for manufacturing a vertical diode in which a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode are stacked adjacent to each other in this order, with the doped layer being adjacent to the first electrode or the second electrode, the method comprising a doping step of forming the doped layer by contacting a surface of an organic semiconductor layer precursor with an aqueous solution containing a fourth oxidizing agent or a fourth reducing agent and a salt of a dopant ion, wherein the dopant ion is a hydrophobic closed shell ion.

35. A method for producing a vertical diode as described in claim 34, wherein the fourth reducing agent is one or more selected from the group consisting of a hydroquinone compound having a hydroquinone skeleton and a reduced coenzyme, and the fourth oxidizing agent is a quinone compound having a quinone skeleton.

36. The method for producing a vertical diode according to claim 34, wherein the doped layer is a layer adjacent to the second electrode, and the method further comprises an electrode modification step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with a surface modification liquid, the surface modification liquid being any one of the following surface modification liquids (S1) to (S4): (S1) A surface modification liquid containing a first reducing agent which reduces the first electrode and generates a low molecular weight hydrophobic cation. (S2) A surface modification liquid containing a first oxidizing agent which oxidizes the first electrode and generates a low molecular weight hydrophobic anion. (S3) A surface modification liquid containing a second reducing agent which reduces the first electrode and a low molecular weight hydrophobic closed shell cation. (S4) A surface modification liquid containing a second oxidizing agent which oxidizes the first electrode and a low molecular weight hydrophobic closed shell anion.

37. The method for producing a vertical diode according to claim 36, wherein the surface modifying liquid is the surface modifying liquid (S1) or the surface modifying liquid (S2).

38. The method for producing a vertical diode according to claim 36, wherein the surface modification liquid is the surface modification liquid (S3) or the surface modification liquid (S4).

39. The method for producing a vertical diode according to claim 36, wherein the solvent of the surface modification liquid is water, and the electrode modification step is carried out in an air atmosphere.

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