Semiconductor device having quantum dots, display device, imaging system, and mobile body

Abstract

The present invention relates to a semiconductor device having quantum dots, a display device, an imaging system, and a moving body. A semiconductor device includes an anode, a cathode, a first functional layer between the anode and the cathode, and a second functional layer between the first functional layer and the cathode. The first functional layer contains first quantum dots having a first ligand, and the second functional layer contains second quantum dots having a second ligand different from the first ligand. The second ligand is an aromatic compound having a sulfur bond and an ester bond.

Description

Technical Field

[0001] One disclosed aspect of the present invention relates to a semiconductor device, a display device, an imaging system, and a mobile body. Background Art

[0002] In many imaging systems such as cameras, for example, a photodiode including an impurity diffusion layer formed on a single-crystalline silicon substrate is used for photoelectric conversion. On the other hand, recently, a photoelectric conversion element having a photoelectric conversion layer containing an organic material or a colloidal quantum dot has been developed. Such materials of the photoelectric conversion layer have higher photosensitivity in the long wavelength region than silicon. US2016 / 0133463 describes a high-sensitivity photoelectric conversion element including a photoelectric conversion layer using a colloidal quantum dot, the colloidal quantum dot having a 1,3-benzenedithiol or 4-mercaptobenzoic acid ligand.

[0003] In the photoelectric conversion element described in U.S. Patent Application Publication No. 2016 / 0133463, charges generated when irradiated with light remain therein. In this state, immediately after irradiation with light, the current value of the photoelectric conversion element is sometimes higher than the current generated by light irradiation, and the current value becomes unstable. In a semiconductor device, such current instability, particularly in a photoelectric conversion element, causes noise. Summary of the Invention

[0004] One disclosed aspect of the present invention provides a semiconductor device having a stable current value when irradiated with light.

[0005] According to one aspect of the present invention, a semiconductor device includes an anode, a cathode, a first functional layer between the anode and the cathode, and a second functional layer between the first functional layer and the cathode. The first functional layer contains first quantum dots having a first ligand, and the second functional layer contains second quantum dots having a second ligand different from the first ligand. The second ligand is an aromatic compound having a sulfur bond and an ester bond.

[0006] With reference to the accompanying drawings, further features of the present disclosure will become apparent from the following description of exemplary embodiments. Brief Description of the Drawings

[0007] Figure 1 is a diagram showing the energy difference between the conduction band minimum (CBM) of a quantum dot and the triplet excitation level (T1) of a ligand of the quantum dot.

[0008] Figure 2A is a schematic cross-sectional view of a semiconductor device according to an embodiment of the present disclosure. Figure 2B is Figure 2ASchematic partial cross-sectional view of the semiconductor device described in [description], showing a part of the semiconductor from the first electrode to the second electrode.

[0009] Figure 3 Is a partial schematic plan view of a semiconductor device according to an embodiment of the present disclosure, showing the configuration of a plurality of first electrodes and an intermediate layer.

[0010] Figures 4A to 4C Is a schematic cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present disclosure.

[0011] Figure 5A Is an example of an imaging device including a display device according to an embodiment of the present disclosure. Figure 5B Is an example of an electronic device including a display device. Figure 5C and Figure 5D Are examples of display devices each including a light-emitting device according to an embodiment of the present disclosure.

[0012] Figure 6A and Figure 6B Are diagrams respectively showing the structures of an imaging system and a moving body according to an embodiment.

[0013] Figure 7 Is a schematic block diagram showing the structure of an imaging system according to an embodiment.

[0014] Figure 8A and Figure 8B Are measurement diagrams of the residue of electrons and the variation of current generated in a device according to an embodiment, respectively. Detailed Description

[0015] The semiconductor device disclosed herein includes a first functional layer and a second functional layer between an anode and a cathode. The first functional layer and the second functional layer contain quantum dots. The anode is an electrode having a potential higher than that of the cathode when driving the semiconductor device. On the other hand, when driving the semiconductor device, the potential of the cathode is lower than that of the anode. The cathode may be grounded. The quantum dots in the second functional layer have ligands different from those of the quantum dots in the first functional layer. The quantum dots in the first functional layer may have a higher external quantum efficiency or photoelectric conversion efficiency than the quantum dots in the second functional layer. The quantum dots in the second functional layer have an aromatic compound ligand containing a sulfur bond and an ester bond. The presence of such ligands in the second functional layer enables the reduction of the number of electrons inadvertently remaining in the first functional layer. Therefore, the semiconductor device may have a stable current value when irradiated with light. In the description disclosed herein, having a sulfur bond means having a bond via a sulfur atom, and the sulfur bond may be derived from a thiol group. The sulfur bond may exist in the form of a thiolate anion. The ester bond mentioned herein is composed of a carbon atom, an oxygen atom double-bonded to the carbon atom in between, and another oxygen atom single-bonded to the carbon atom in between (defined). The ester bond may be derived from a carboxyl group. The carboxyl group may exist in the form of a carboxylate. Examples of aromatic compounds having both a sulfur bond and an ester bond include mercaptobenzoic acid (MBA), mercaptonaphthoic acid, and mercaptophenanthroic acid. In some embodiments, mercaptobenzoic acid or mercaptonaphthoic acid may be used.

[0016] Instability of the current during light irradiation causes, for example, image lag or photocurrent fluctuation. Image lag is a phenomenon in which electrons generated in the photoelectric conversion layer are not completely transferred by one scan and remain until the next scan. In this case, the device cannot respond to a sudden change in the incident light intensity and forms a picture that looks like a trailing in actual video shooting. Image lag should be reduced. Photocurrent fluctuation is a phenomenon in which the photocurrent fluctuates even when the incident light intensity remains constant. Although the light intensity is constant, a bright picture is formed during actual image shooting. Reduced photocurrent fluctuation is desirable.

[0017] In the case of a light-emitting device, if image lag or photocurrent fluctuation occurs, light having a higher brightness than the desired brightness may be emitted. In order to also be used in a light-emitting device, reduced current instability is desirable.

[0018] Role of MBA in reducing image lag

[0019] In a semiconductor device according to an embodiment of the present disclosure, mercaptobenzoic acid (MBA) is used to reduce the migration of electrons to an adjacent layer, thereby stabilizing the photocurrent to reduce image lag.

[0020] When a bias voltage is applied to a photoelectric conversion element, charge carriers injected from an electrode or generated by light irradiation remain in the photoelectric conversion element and are detected as signals even in the dark state after interruption of light irradiation. Thereby, image lag occurs. The photocurrent fluctuation may be caused by the temporal accumulation of holes or electrons during light irradiation. In the embodiments disclosed herein, MBA is used in the functional layer 133C ( Figure 2B shown in) to reduce the injection of electrons from the second electrode mainly used to apply a negative bias voltage into the functional layer 133B ( Figure 2B shown in), thereby reducing image lag.

[0021] In other words, a semiconductor device having a quantum dot film containing MBA between the second electrode 134 and the functional layer 133B mainly functioning as a light absorber hinders electrons generated in the functional layer 133B from reaching the second electrode 134 that collects holes. In addition, such a semiconductor device enables electrons generated in the functional layer 133B to effectively reach the first electrode 131 that collects electrons. In contrast, a semiconductor device including a quantum dot film containing MBA between the first electrode 131 and the functional layer 133B does not hinder electrons generated in the functional layer 133B from reaching the second electrode 134 that collects holes.

[0022] It is possible that the reason for the reduction in electron migration between layers due to the presence of MBA is not the energy level difference but the low ability of electron migration. This is indicated by the fact that the energy levels of mercaptopropionic acid (MPA) that cannot effectively reduce image lag are equivalent to those of MBA. To support this reason, the HOMO energy levels of quantum dot films respectively coordinated with 4-MBA, 3-MBA, 2-MBA, 1,3-benzenedithiol (1,3-BDT), MPA, and PbI2 were measured using an atmospheric photoelectron spectrometer AC-3 (manufactured by Riken Keiki).

[0023] The quantum dot film coordinated with 4-MBA shows a HOMO energy level at 5.3 eV; the quantum dot film coordinated with 3-MBA shows a HOMO energy level at 5.2 eV; the quantum dot film coordinated with 2-MBA shows a HOMO energy level at 5.2 eV; the quantum dot film coordinated with 1,3-BDT shows a HOMO energy level at 5.2 eV; the quantum dot film coordinated with MPA shows a HOMO energy level at 5.3 eV; and the quantum dot film coordinated with PbI2 shows a HOMO energy level at 5.6 eV. Since the difference in HOMO energy levels between MBA and MPA is small, these ligand substances basically have no difference in charge blocking performance caused by the energy level difference. Therefore, the reason for the effect of reducing image lag is not the energy level difference between MPA and MBA. The present inventors believe that the small electron mobility of MBA produces the effect of reducing image lag. Therefore, in the case of a structure including a first functional layer and a second functional layer between the first functional layer and the cathode, it is beneficial to endow the second functional layer with a lower electron mobility than the first functional layer.

[0024] According to the research of the present inventors, in order to form a quantum dot film that can reduce electron migration and can be used as a quantum dot film coordinated with MBA, it is effective to reduce the energy difference between the lowest conduction band energy level (CBM) of the quantum dot and the triplet excitation energy level (T1) of the ligand of the quantum dot. Additionally, it is beneficial to reduce the energy difference between the CBM of the quantum dot and the singlet excitation energy level (S1) of the ligand of the quantum dot. In other words, it is beneficial that the energy difference between T1 of the ligand of the quantum dot in the second functional layer and the CBM of the quantum dot is smaller than the energy difference between T1 of the ligand of the quantum dot in the first functional layer and the CBM of the quantum dot. Additionally, it is beneficial that the energy difference between S1 of the ligand of the quantum dot in the second functional layer and the CBM of the quantum dot is smaller than the energy difference between S1 of the ligand of the quantum dot in the first functional layer and the CBM of the quantum dot.

[0025] More specifically, the difference between the CBM energy of the quantum dot in the second functional layer and the T1 energy of the ligand of the quantum dot can be 0.8 eV or less. In one embodiment, the difference between the CBM energy of the quantum dot in the second functional layer and the T1 energy of the ligand of the quantum dot can be 0.3 eV or less. Additionally, the difference between the CBM energy of the quantum dot and the S1 energy of the ligand of the quantum dot can be 0.3 eV or less. The S1 energy refers to the lowest excited singlet energy or singlet excitation energy, and the T1 energy refers to the lowest excited triplet energy or triplet excitation energy.

[0026] Figure 1It is a graph showing the energy difference between the CBM and T1 that depends on the ligand substance. The CBM is the CBM of PbS. The vertical axis of the graph represents the approximate difference between the CBM and T1, and the horizontal axis represents the ligands: MBA, BDT, and MPA. MBA gives the smallest difference among the three ligands, and the energy difference between the CBM and T1 is less than 0.3 eV. BDT gives an intermediate energy difference of approximately 0.9 eV among the three ligands. MPA gives the largest difference among the three ligands, and the energy difference between the CBM and T1 is 1.0 eV or more. The solid line in the graph represents the energy level of 1.0 eV, and the dashed line represents the energy level of 0.8 eV. Compounds with an energy difference between the CBM and T1 of 0.8 eV or less have the same effect as MBA.

[0027] It is possible that the energy difference between the CBM and T1 has the following relationship for reducing electron migration. For example, in addition to having an aromatic ring, MBA has the same chemical structure as MPA, and as described above, the difference in HOMO energy levels between them is not large. However, the external quantum efficiency (EQE) of MBA is low, and the EQE of MPA is higher than that of MBA. The difference in EQE between MBA and MPA may cause a difference in charge transportability. The charge transportability of organic ligands is explained using the energy levels in the ground state (S0), singlet excited state (S1), and triplet excited state (T1) of the electronic state of the organic ligand.

[0028] The S1 energy levels of MPA and MBA are higher than the CBM of the quantum dot. Comparing these two ligands, the S1 energy level of MBA with an aromatic ring is lower than that of MPA. The T1 energy level of MBA is also lower than that of MPA. Therefore, the T1 energy level of MBA is closer to the CBM energy level of the quantum dot than that of MPA. Different from MPA, MBA with an aromatic ring is stabilized due to the interaction between the orbitals of the quantum dot and MBA. Therefore, the S1 and T1 energy levels of MBA can be further reduced, promoting the energy resonance between the quantum dot and the organic ligand.

[0029] As described above, compared with MBA, MPA gives a larger energy difference between the CBM and T1 energy levels of the quantum dot. Therefore, the electrons generated in the quantum dot migrate to adjacent quantum dots without exciting the MPA ligand.

[0030] In quantum dots with the MBA ligand, compared with quantum dots with the MPA ligand, the electrons generated in the quantum dot are more likely to excite MBA, and the electrons migrating to adjacent quantum dots are reduced. As a result, quantum dots with the MPA ligand show high EQE, while quantum dots with the MBA ligand show low EQE.

[0031] In a semiconductor device including a quantum dot film containing MBA between a first electrode 131 and a functional layer 133B, the number of electrons generated per unit time in the functional layer 133B and reaching the first electrode 131 is thereby reduced, and the EQE is significantly decreased.

[0032] In the above embodiment, MBA is used as a ligand having a benzene skeleton. In one embodiment, the ligand may be a compound having a plurality of benzene rings, for example, a naphthalene skeleton or an anthracene skeleton may be used. This is because the energy gap between the S0 and S1 states of molecules of such skeletons is smaller than that of the benzene skeleton, and they have reduced S1 and T1 energy levels, and thus, electron migration from the quantum dots to the ligand can be induced. Therefore, electron migration between the layers is reduced; thus, the same effect as described above is produced.

[0033] Since the CBM of the quantum dots varies according to the particle size of the quantum dots, the energy difference between the CBM of the quantum dots and the T1 of the ligand can be controlled by selecting an appropriate particle size of the quantum dots. For example, the CBM can be increased by reducing the particle size of the quantum dots to less than 3.0 mm, as long as the quantum dots can sufficiently absorb light in the desired wavelength range. A high CBM means a shallow CBM. Advantageously, the CBM energy level is higher than the T1 energy level.

[0034] The present inventors have thus found that a multilayer element using MBA as an organic ligand having a thiol group and a carboxyl group as functional groups is effective in reducing image lag. Generally, a quantum dot film coordinated with 4-MBA alone is not suitable as a main light absorption layer of a photoelectric conversion element because of its low EQE. However, in the case of using a quantum dot film coordinated with 4-MBA as the functional layer 133C of a component of a multilayer element, improved performance is provided not only in terms of EQE but also in terms of image lag and photocurrent fluctuation.

[0035] Exemplary embodiments of the present disclosure will now be described with reference to the drawings. The embodiments described below are merely some exemplary embodiments of the concept of the present disclosure, and the present disclosure is not limited to the disclosed values and structures, including shapes, forms, materials, and configurations or connection relationships of components or members. For example, although the semiconductor device of the concept of the present invention is implemented as a photoelectric conversion device in the embodiments described below, in other embodiments, the semiconductor device may be implemented as a light-emitting device. Additionally, the conductive types of the transistors and semiconductor regions used in the following embodiments may be changed as needed.

[0036] The same components or elements are denoted by the same reference numerals or symbols in all the drawings, and thus, in some cases, the description may be omitted or simplified. Additionally, in the drawings in which there are a plurality of identical elements or components in the configuration or structure, the reference numerals or symbols of the identical elements and their descriptions may be omitted.

[0037] Structure of the semiconductor device

[0038] Figure 2A It is a schematic cross-sectional view of a semiconductor device according to an embodiment of the present disclosure. Figure 2A It shows a cross-section of the semiconductor device taken at a plane composed of the Z direction (the upward direction of the figure) and the X direction (the rightward direction of the figure). The semiconductor device of the illustrated embodiment is a photoelectric conversion device that converts incident light into electricity to generate charges according to the amount of the incident light. Figure 2A It shows three unit cells 120 of the semiconductor device. The unit cell 120 is usually referred to as a sub-pixel. The three unit cells 120 may have the same circuit structure as each other. Each unit cell 120 includes at least one photoelectric conversion element.

[0039] In one embodiment, the semiconductor device may be a light-emitting device. In such a case, the unit cell 120 includes at least one light-emitting element. The semiconductor device functions as a photoelectric conversion device or a light-emitting device depending on the material of the functional layer of the unit cell 120.

[0040] The semiconductor device includes a substrate 100. The substrate 100 in the illustrated embodiment is a single-crystalline silicon substrate or any other semiconductor substrate, but in other embodiments, it may be an insulator substrate made of glass, ceramic, or the like. The substrate 100 has a main surface P1. The substrate 100 is provided with a transistor 101 and an element isolation portion 113 at the main surface P1. Providing the transistor at the main surface P1 means forming an impurity region on the surface of the semiconductor substrate to define a region where a channel can be formed.

[0041] The transistor 101 may be an N-type MOS transistor including source / drain regions 102, a gate insulating film 103, a gate electrode 104, and source / drain regions 105. The gate insulating film 103 and the gate electrode 104 are formed on the main surface P1. The gate insulating film 103 is disposed between the gate electrode 104 and the main surface P1. The source / drain regions 102 and 105 are disposed inside the substrate 100. For the N-type MOS transistor 101, the source / drain regions 102 and 105 are N-type semiconductor regions. The element isolation portion 113 may have a structure for shallow trench isolation (STI).

[0042] The wiring structure 106 is disposed on the main surface P1 of the substrate 100. The wiring structure 106 includes contact plugs 107, wiring layers 108, via plugs 109, wiring layers 110, via plugs 111, and an insulating layer 112. The insulating layer 112 may be composed of a single layer or multiple layers. These components may be formed of any metal, insulating material, and other materials commonly used in semiconductor processes.

[0043] The contact plugs 107 and the via plugs 109 and 111 may be made of materials selected from the group including aluminum, copper, tungsten, titanium, and titanium nitride. Typically, the contact plugs 107 and the via plugs 109 and 111 may be formed in a multilayer structure formed of titanium, titanium nitride, and tungsten. The wiring layers 108 and 110 may be made of materials selected from the group including aluminum, copper, tungsten, titanium, titanium nitride, and tantalum.

[0044] Typically, the wiring layers 108 and 110 may be formed in a multilayer structure formed of tantalum and copper. The insulating layer 112 may be made of silicon oxide or silicon nitride.

[0045] The wiring structure 106 includes a plurality of first electrodes 131 disposed spaced apart from each other. The plurality of first electrodes 131 are disposed in each of the unit cells 120. A separation region 130 exists between each first electrode 131 and the next first electrode 131. The separation region 130 may be defined by the structural layer 112 of the wiring structure 106. Each first electrode 131 is coupled to a corresponding via plug 111. The first electrode 131 may be made of copper, aluminum, or the like.

[0046] The semiconductor device further includes an intermediate layer 132, a functional layer 133, and a second electrode 134. The intermediate layer 132, the functional layer 133, and the second electrode 134 are sequentially disposed on the wiring structure 106. The second electrode 134 may be formed continuously across three unit cells 120. In the illustrated embodiment, the second electrode 134 has a flat upper surface and a lower surface. Thus, the semiconductor device has a plurality of first electrodes, a functional layer, and a second electrode, and the functional layer is shared by the plurality of first electrodes. In other words, the semiconductor device includes one functional layer, one second electrode, and a plurality of first electrodes. The first electrode may be an anode, and the second electrode may be a cathode. An anode is an electrode whose potential is higher than that of other electrodes, the cathode, during driving. The anode collects electrons and is also called the positive electrode.

[0047] The functional layer 133 is disposed between the plurality of first electrodes 131 and the second electrode 134. The functional layer 133 is a photoelectric conversion layer and can detect light. The first electrode 131 may be used to read out a signal generated based on the charge generated by photoelectric conversion.

[0048] In an embodiment in which a semiconductor device is applied as a light-emitting device, the driving functional layer 133 emits light. In this case, in order to control whether to emit light and to control the light-emitting intensity, the first electrode 131 is used to transmit a control signal to the functional layer 133.

[0049] The intermediate layer 132 is disposed between the discrete first electrode 131 and the functional layer 133. The intermediate layer 132 electrically insulates one of holes or electrons between the first electrode 131 and the functional layer 133, and conducts the other of holes or electrons. Accordingly, the intermediate layer 132 may be referred to as a carrier injection / blocking layer. In an embodiment in which the first electrode 131 is a cathode (negative electrode) for collecting holes, the intermediate layer 132 may be an electron blocking layer for blocking electrons and conducting holes. In an embodiment in which the first electrode 131 is an anode (positive electrode) for collecting electrons, the intermediate layer 132 may be a hole blocking layer for blocking holes and conducting electrons. In the case where the intermediate layer 132 functions as an electron blocking layer, a hole blocking layer (not shown) may be provided between the functional layer 133 and the second electrode 134. In the case where the intermediate layer 132 functions as a hole blocking layer, an electron blocking layer (not shown) may be provided between the functional layer 133 and the second electrode 134.

[0050] The intermediate layer 132 may function as an adhesion layer between each first electrode 131 and the functional layer 133. The intermediate layer 132 disposed between the first electrode 131 and the functional layer 133 may reduce peeling between the first electrode 131 and the functional layer 133 caused by low wettability therebetween. In some embodiments, from the viewpoint of increasing the contact area between the intermediate layer 132 and the functional layer 133 and thereby reducing peeling, the intermediate layer 132 is formed on the entire surface of the wiring structure 106. The portion from any one of the first electrodes to the second electrode is referred to as a photoelectric conversion element. The photoelectric conversion element may include a photoelectric conversion layer and an intermediate layer disposed between the photoelectric conversion layer and one of the electrodes. More specifically, the intermediate layer is an electron blocking layer and a hole blocking layer.

[0051] The semiconductor device further includes an insulating layer 136, a color filter layer 137, a planarization layer 138, and a microlens layer 139. The insulating layer 136, the color filter layer 137, the planarization layer 138, and the microlens layer 139 are sequentially disposed on the second electrode 134. The insulating layer 136 may function as a protective layer and a sealing layer. The color filter layer 137 includes each color filter for any of a plurality of colors. Each unit cell 120 includes a color filter for the corresponding color. The planarization layer 138 has a flat upper surface suitable for forming the microlens layer 139. The microlens layer 139 includes a plurality of microlenses. A single unit cell 120 includes a single microlens. The color filters may be arranged in a Bayer array.

[0052] Figure 2B is Figure 2A A schematic partial cross-sectional view of the semiconductor device described in Figure 2B , showing a portion from any one of the first electrodes to the second electrode. As described above, the first electrode (anode) 131, the intermediate layer 132, the functional layer 133 (the third functional layer 133A, the first functional layer 133B, and the second functional layer 133C), and the second electrode (cathode) 134 are formed in sequence. As Figure 2A described in Figure 2A , the semiconductor device has a plurality of first electrodes 131. Each first electrode shares each other component formed on the first electrode. More specifically, for the plurality of first electrodes, a single functional layer structure and a single second electrode are provided. The structure in which these layers are shared by the first electrodes shown is an example, and in one embodiment, the plurality of first electrodes may be provided with their respective functional layer structures and second electrodes.

[0053] Figure 3 is a partial schematic plan view of the semiconductor device according to an embodiment of the present disclosure, showing the configuration of the plurality of first electrodes 131 and the intermediate layer 132. The schematic plan view shows a portion of the semiconductor device observed from a direction perpendicular to the main surface P1. For the photoelectric conversion device, the unit cell 120 is arranged in a matrix having multiple rows and multiple columns, corresponding to the regions defined by the respective first electrodes 131. The intermediate layer 132 is disposed on all the first electrodes 131 and the separation region 130 and spans all the first electrodes 131 and the separation region 130. Therefore, as described above, the contact area between the intermediate layer 132 and the functional layer 133 is increased, effectively reducing peeling therebetween.

[0054] Materials of the functional layer and the intermediate layer of the semiconductor device

[0055] Now, the material of the functional layer 133 of the semiconductor device disclosed herein will be described. As described above, the functional layer 133 functions as a photoelectric conversion layer, and its material and production method are not otherwise limited. The functional layer 133 may include a colloidal quantum dot film composed of aggregates of nanoparticles such as compound semiconductors.

[0056] Ligands of the quantum dots

[0057] The quantum dots used in the semiconductor devices disclosed herein have ligands. The ligands have thiol groups, but are not limited to 1,3-benzenedithiol (BDT). Ligand substances having a benzene ring, including 1,4-BDT and 1,2-BDT, etc., have a boiling point of 200 °C or higher. Such ligands are unlikely to detach or volatilize from the surface of the quantum dots even under the condition of 140 °C, and are effective in improving the heat resistance of the quantum dots. The ligands of the quantum dots are bound to the inorganic particles constituting the quantum dots. In other words, the ligands of the quantum dots can be referred to as components of the quantum dots. Examples of ligands having thiol groups include 4-methyl-1,2-benzenedithiol, 1,3,5-benzenetrithiol, 5-bromo-1,3-benzenedithiol, 4-chloro-1,3-benzenedithiol, 3,6-dichloro-1,2-benzenedithiol, 4,6-dichloro-1,3-benzenedithiol, 2,5-diamino-1,4-benzenedithiol, 4,6-diamino-1,3-benzenedithiol, 1,2,4,5-benzenetetrathiol, 3,4,5,6-tetrachloro-1,2-benzenedithiol, 3,4,5,6-tetrafluoro-1,2-benzenedithiol, 3-methyl-1,2-benzenedithiol, 4,5-dimercapto-1,2-benzenedicarbonitrile, and 4-fluoro-1,2-benzenedithiol. Ligands having thiol groups may have a naphthalene skeleton, and examples thereof include 2,6-naphthalenedithiol, 1,5-naphthalenedithiol, 2,7-naphthalenedithiol, 1,8-naphthalenedithiol, and 1,4-naphthalenedithiol. The external quantum efficiency EQE (or the photoelectric conversion efficiency) depends on the distance between each colloidal quantum dot and the next colloidal quantum dot, and this distance changes according to the ligand used. Therefore, it is beneficial to reduce the size of the ligand molecules.

[0058] The ligand can have a thiol group and an aromatic ring having a carboxyl group. Such ligands can be, but are not limited to, 4-mercaptobenzoic acid (4-MBA). Examples of such ligands include 5-bromo-2-mercaptobenzoic acid, 4-fluoro-2-mercaptobenzoic acid, 4-amino-3-mercaptobenzoic acid, 5-chloro-2-mercaptobenzoic acid, 5-fluoro-2-mercaptobenzoic acid, 4-bromo-2-mercaptobenzoic acid, 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid, 4-amino-5-mercapto-2-methoxybenzoic acid, 2-bromo-4-mercaptobenzoic acid, 4-chloro-2-mercaptobenzoic acid, 4-fluoro-3-mercaptobenzoic acid, 2-chloro-4-mercaptobenzoic acid, 2-chloro-5-mercaptobenzoic acid, 2-mercapto-3-methylbenzoic acid, 4-mercapto-2-methoxybenzoic acid, 2-mercapto-5-methoxybenzoic acid, 5-mercapto-2-methoxy-4-methylbenzoic acid, 5-mercapto-2-nitrobenzoic acid, 3-chloro-4-mercaptobenzoic acid, 4-amino-3-mercapto-5-methoxybenzoic acid, 2-fluoro-5-mercaptobenzoic acid, 2-mercapto-5-methylbenzoic acid, 2-mercapto-5-nitrobenzoic acid, 2-bromo-5-mercaptobenzoic acid, 4-mercapto-1,3-benzenedicarboxylic acid, 2-chloro-6-mercaptobenzoic acid, 2-fluoro-4-mercaptobenzoic acid, 2-mercapto-4-methylbenzoic acid, 3,5-dichloro-2-mercaptobenzoic acid, 3-mercapto-4-nitrobenzoic acid, 2-mercapto-4-methoxybenzoic acid, 5-amino-2-mercaptobenzoic acid, 4-mercapto-1,2-benzenedicarboxylic acid, 3,5-dimercaptobenzoic acid, 2-mercapto-3,5-dimethylbenzoic acid, 2-mercapto-4,5-dimethoxybenzoic acid, 4-mercapto-3-nitrobenzoic acid, 3-hydroxy-5-mercapto-4-methoxybenzoic acid, 3-chloro-2-mercaptobenzoic acid, 2,5-dimercapto-1,4-benzenedicarboxylic acid, 2-mercapto-1,4-benzenedicarboxylic acid, 4-amino-2-mercaptobenzoic acid, 5-mercapto-2-methoxybenzoic acid, 2-fluoro-6-mercaptobenzoic acid, 5-mercapto-1,3-benzenedicarboxylic acid, 4-bromo-3-mercaptobenzoic acid, 4-mercapto-3-methylbenzoic acid, 2-mercapto-6-methylbenzoic acid, 4-chloro-3-mercaptobenzoic acid, 3,5-dibromo-2-mercaptobenzoic acid, 3-mercapto-4-methoxybenzoic acid, 5-mercapto-2-methylbenzoic acid, 5-acetyl-2-mercaptobenzoic acid, 5-chloro-2-mercapto-3-methylbenzoic acid, 3-mercapto-2-methylbenzoic acid, 5-mercapto-1,3-benzenedicarboxylic acid 1-methyl ester, 3-mercapto-4-methyl-5-nitrobenzoic acid, 3-fluoro-2-mercaptobenzoic acid, 3-amino-4-mercaptobenzoic acid, 2-mercapto-5-(trifluoromethyl)benzoic acid, 2,4-dichloro-5-mercaptobenzoic acid, 4-amino-2-ethoxy-5-mercaptobenzoic acid, 4-hydroxy-3-mercaptobenzoic acid, 2-mercapto-3,6-dimethylbenzoic acid, 3-fluoro-4-mercaptobenzoic acid, 5-hydroxy-2-mercaptobenzoic acid, 5-mercapto-2,4-dimethylbenzoic acid,5-Iodo-2-mercaptobenzoic acid, 5-mercapto-2,3-dimethoxybenzoic acid, 4-fluoro-5-mercapto-2-nitrobenzoic acid, 2-amino-3-mercaptobenzoic acid, 4-chloro-3-mercapto-5-methylbenzoic acid, 2,3-difluoro-5-mercaptobenzoic acid, 3-chloro-2-fluoro-5-mercaptobenzoic acid, 5-cyano-2-mercapto-4-methylbenzoic acid, 2-(aminomethyl)-4-cyano-6-mercaptobenzoic acid, 2-cyano-6-mercapto-4-methylbenzoic acid, 4-(bromomethyl)-2-cyano-6-mercaptobenzoic acid, 5-chloro-2-cyano-4-mercaptobenzoic acid, 2-cyano-6-ethyl-4-mercaptobenzoic acid, 4-cyano-5-ethyl-2-mercaptobenzoic acid, 2-(bromomethyl)-4-cyano-3-mercaptobenzoic acid, 6-(bromomethyl)-3-cyano-2-mercaptobenzoic acid, 6-chloro-2-cyano-3-mercaptobenzoic acid, 2-cyano-5-ethyl-3-mercaptobenzoic acid, 4-(aminomethyl)-2-cyano-3-mercaptobenzoic acid, 5-(aminomethyl)-2-cyano-4-mercaptobenzoic acid, 2-cyano-3-ethyl-6-mercaptobenzoic acid, 3-cyano-4-ethyl-5-mercaptobenzoic acid, 6-cyano-2-ethyl-3-mercaptobenzoic acid, 2-(aminomethyl)-5-cyano-4-mercaptobenzoic acid, 2-(bromomethyl)-5-cyano-4-mercaptobenzoic acid, 2-(bromomethyl)-3-cyano-6-mercaptobenzoic acid, 5-(bromomethyl)-2-cyano-3-mercaptobenzoic acid, 4-(bromomethyl)-3-cyano-5-mercaptobenzoic acid, 5-chloro-4-cyano-2-mercaptobenzoic acid, 3-(chloromethyl)-2-cyano-6-mercaptobenzoic acid, 4-(chloromethyl)-5-cyano-2-mercaptobenzoic acid, 2-(bromomethyl)-6-cyano-3-mercaptobenzoic acid, 2-(chloromethyl)-3-cyano-4-mercaptobenzoic acid, 3-(chloromethyl)-2-cyano-5-mercaptobenzoic acid, 3-chloro-2-cyano-5-mercaptobenzoic acid, 3-cyano-5-mercapto-2-methylbenzoic acid, 2-(aminomethyl)-6-cyano-3-mercaptobenzoic acid, 3-cyano-2-ethyl-6-mercaptobenzoic acid, 3-(bromomethyl)-2-cyano-5-mercaptobenzoic acid, 2-chloro-3-cyano-5-mercaptobenzoic acid, 3-chloro-6-cyano-2-mercaptobenzoic acid, 2-(aminomethyl)-5-cyano-3-mercaptobenzoic acid, 5-(bromomethyl)-3-cyano-2-mercaptobenzoic acid, 3-chloro-2-cyano-4-mercaptobenzoic acid, 4-cyano-3-ethyl-2-mercaptobenzoic acid, 2-(chloromethyl)-3-cyano-5-mercaptobenzoic acid, 3-(chloromethyl)-4-cyano-2-mercaptobenzoic acid, 4-chloro-3-cyano-5-mercaptobenzoic acid, 2-(chloromethyl)-5-cyano-3-mercaptobenzoic acid, 2-cyano-4-mercapto-5-methylbenzoic acid, 5-cyano-3-mercapto-2-methylbenzoic acid, 2-cyano-4-ethyl-5-mercaptobenzoic acid,3-Cyano-5-ethyl-4-mercaptobenzoic acid, 4-cyano-3-mercapto-2-methylbenzoic acid, 2-(aminomethyl)-6-cyano-4-mercaptobenzoic acid, 2-(bromomethyl)-3-cyano-4-mercaptobenzoic acid, 6-(bromomethyl)-2-cyano-3-mercaptobenzoic acid, 4-(chloromethyl)-3-cyano-2-mercaptobenzoic acid, 3-(bromomethyl)-6-cyano-2-mercaptobenzoic acid, 3-(bromomethyl)-4-cyano-5-mercaptobenzoic acid, 5-(bromomethyl)-4-cyano-2-mercaptobenzoic acid, 6-(chloromethyl)-3-cyano-2-mercaptobenzoic acid, 5-cyano-2-ethyl-3-mercaptobenzoic acid, 2-chloro-3-cyano-6-mercaptobenzoic acid, 3-chloro-4-cyano-2-mercaptobenzoic acid, 6-cyano-2-mercapto-3-methylbenzoic acid, 3-(chloromethyl)-4-cyano-5-mercaptobenzoic acid, 2-cyano-4-ethyl-6-mercaptobenzoic acid, 6-cyano-3-ethyl-2-mercaptobenzoic acid, 2-chloro-3-fluoro-4-mercaptobenzoic acid, 5-mercapto-2,4-dimethoxybenzoic acid, 2-mercapto-6-methyl-3-(1-methylethyl)benzoic acid, 2-mercapto-3-methoxybenzoic acid, 2-hydroxy-4-mercaptobenzoic acid, 2-mercapto-3,6-dimethoxybenzoic acid, 4,5-diethoxy-2-mercaptobenzoic acid, 3-mercapto-2-nitrobenzoic acid, 3,5-difluoro-4-mercaptobenzoic acid, 3-mercapto-4-methylbenzoic acid, 4-ethyl-3-mercaptobenzoic acid, 4-mercapto-3-methoxybenzoic acid, 4,5-difluoro-2-mercaptobenzoic acid, 2,5-dichloro-3-mercaptobenzoic acid, 2-bromo-3-mercapto-5-methylbenzoic acid, 5-chloro-2-iodo-3-mercaptobenzoic acid, 3-fluoro-5-mercapto-4-methoxybenzoic acid, 3-chloro-4-fluoro-5-mercaptobenzoic acid, 2-bromo-5-fluoro-3-mercaptobenzoic acid, 2,6-difluoro-3-mercaptobenzoic acid, 3,4-dichloro-5-mercaptobenzoic acid, 3-fluoro-5-mercapto-4-methylbenzoic acid, 3-bromo-5-mercapto-4-methylbenzoic acid, 2,3-dichloro-5-mercaptobenzoic acid, 3-chloro-4-iodo-5-mercaptobenzoic acid, 3-chloro-5-mercapto-2-methylbenzoic acid, 5-mercapto-4-methyl-2-nitrobenzoic acid, 2-mercapto-4-(trifluoromethyl)benzoic acid, 2,3-dichloro-4-mercaptobenzoic acid, 2-hydroxy-5-mercaptobenzoic acid, 5-(1,1-dimethylethyl)-2-mercapto-1,3-benzenedicarboxylic acid, 5-(aminosulfonyl)-2-mercaptobenzoic acid, 3-amino-2-mercaptobenzoic acid, 4-mercapto-2-nitrobenzoic acid, 3-mercapto-4-methyl-2-nitrobenzoic acid, 2-mercapto-6-(methylthio)benzoic acid, 5-mercapto-2,3-dimethylbenzoic acid, 2-mercapto-4,6-dimethylbenzoic acid, 3-mercapto-4,5-dimethylbenzoic acid, 3-(1,1-dimethylethyl)-4-mercaptobenzoic acidand 4-chloro-3-mercapto-2-methylbenzoic acid. Ligands having a thiol group and an aromatic ring containing a carboxyl group may have a naphthalene skeleton, and examples of such ligands include 3-mercapto-2-naphthoic acid and 6-mercapto-1-naphthoic acid. The external quantum efficiency EQE depends on the distance between the respective colloidal quantum dots, and this distance changes depending on the ligand used. Therefore, it is beneficial to reduce the size of the ligand molecule.

[0059] Embodiments using the functional layer 133 composed of colloidal quantum dots including semiconductor nanoparticles will now be described. The colloidal quantum dots include nanoparticles having an average particle size of 0.5 nm or more and less than 100 nm. The material of the nanoparticles may be a single-element semiconductor (Group IV semiconductor) or a compound semiconductor. The compound semiconductor may be a III-V group semiconductor compound, a II-VI group semiconductor compound, or a semiconductor compound composed of a combination of three or more elements selected from Groups II, III, IV, V, and VI. More specifically, examples of the material of the nanoparticles include PbS, PbSe, PbTe, InN, InAs, InP, InSb, InAs, InGaAs, CdS, CdSe, CdTe, Ge, CuInS, CuInSe, CuInGaSe, and Si. The band gaps of these semiconductors are relatively narrow. The colloidal quantum dots may be composed of the same kind of nanoparticles or two or more kinds of nanoparticles. The colloidal quantum dots made of such materials are also called semiconductor quantum dots. The nanoparticles may have a core-shell structure including a core containing a semiconductor and a shell covering the core.

[0060] The nanoparticles can be set to a size less than or close to the exciton Bohr radius of the semiconductor. In this case, the quantum size effect appears and a desired band gap is given to the nanoparticles according to the size of the particles. Therefore, the light absorption wavelength or the emission wavelength is controlled by forming a quantum dot film having nanoparticles controlled to a predetermined size.

[0061] In some embodiments, from the viewpoint of ease of synthesis, the nanoparticles are made of PbS or PbSe. Since the exciton Bohr radius of PbS is about 18 nm, from the viewpoint of controlling crystal growth and the appearance of the quantum size effect, the average particle size of the nanoparticles can be in the range of 2 nm to 15 nm. In terms of the control of crystal growth, nanoparticles having an average particle size of 2 nm or more are easily synthesized. The size of the nanoparticles can be measured under a transmission electron microscope.

[0062] There is no particular limitation on the thickness of the functional layer 133, but from the viewpoint of achieving high light absorbability, it may be 10 nm or more, or 50 nm or more. In addition, from the viewpoint of ease of formation, the thickness of the functional layer 133 may be 800 nm or less.

[0063] Now, the material of the intermediate layer 132 of the semiconductor device disclosed herein will be described. As described above, depending on the type of carriers controlled by the first electrode 131, the intermediate layer 132 can be an electron blocking layer or a hole blocking layer. Additionally, the intermediate layer 132 serves as an adhesion layer to reduce the delamination of the functional layer 133.

[0064] First, an embodiment in which the intermediate layer 132 is used as an electron blocking layer will be described. The electron blocking layer can be made of a material that can effectively transport holes generated in the functional layer 133 serving as a photoelectric conversion layer to the cathode and hinder the migration of electrons generated in the functional layer to the cathode. The material of the electron blocking layer can have a high hole mobility and a high conductivity, and have a low barrier for hole injection into the cathode and a low barrier for electron injection from the photoelectric conversion layer into the electron blocking layer. For a semiconductor device in which light enters the photoelectric conversion layer through the electron blocking layer, the electron blocking layer can be made of a transparent material. In this case, the visible light transmittance of the electron blocking layer can be 60% or more or 80% or more. Therefore, the electron blocking layer can be made of a P-type inorganic semiconductor such as molybdenum oxide (MoO3) or nickel oxide (NiO), or a P-type organic semiconductor such as PEDOT:PSS.

[0065] For a semiconductor device used as a light-emitting device, the electron blocking layer can be disposed between the anode and the functional layer. In this case, the electron blocking layer serves as a layer that hinders the migration of electrons from the functional layer to the anode.

[0066] Next, an embodiment in which the intermediate layer 132 is used as a hole blocking layer will be described. Contrary to the electron blocking layer, the hole blocking layer has the function of blocking holes generated in the functional layer and transporting electrons to the anode. Therefore, the advantageous properties of the hole blocking layer can be interpreted as the properties of the electron blocking layer in which the anode and the P-type semiconductor are replaced by the cathode and the N-type semiconductor, respectively, as described above. For a semiconductor device in which light enters through the anode or uses the light reflected from the anode, a transparent material can be used to form the hole blocking layer. Therefore, the hole blocking layer can be made of an N-type wide-band semiconductor such as titanium oxide (TiO2) or zinc oxide (ZnO), or an N-type semiconductor such as fullerene (C 60 ) etc. The inorganic oxide semiconductor is less soluble in the quantum dot dispersion liquid coated on the surface during the manufacturing process and is thus beneficial.

[0067] For a semiconductor device used as a light-emitting device, the hole blocking layer can be disposed between the cathode and the functional layer. In this case, the hole blocking layer serves as a layer that hinders the migration of holes from the functional layer to the anode.

[0068] The thickness of the intermediate layer 132 can be, but is not limited to, about 1 nm to 100 nm. The thin intermediate layer 132 reduces the voltage applied to the functional layer 133. In contrast, the thick intermediate layer 132 reduces the risk of tunneling of electrons or holes through the intermediate layer 132. In addition, the thick intermediate layer 132 reduces the occurrence of pinholes and other film defects. For example, an intermediate layer 132 having a thickness greater than the surface roughness of the first electrode 131 can reduce film defects. From these viewpoints, the thickness of the intermediate layer 132 can be appropriately set.

[0069] Other components of the semiconductor device

[0070] Now, the materials of the first electrode 131 and the second electrode 134 of the semiconductor device disclosed herein will be described. The first electrode 131 and the second electrode 134 can be made of any conductive material. Examples of the materials of the first electrode 131 and the second electrode 134 include elemental metals such as, for example, platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, and magnesium, and alloys containing two or more such metals. Alternatively, the first electrode 131 and the second electrode 134 can be made of metal oxides such as, for example, indium oxide or tin oxide, or composite oxides containing such metal oxides such as, for example, ITO (indium tin oxide) or IZO (indium zinc oxide). The materials of the first electrode 131 and the second electrode 134 can be conductive particles such as carbon black, fullerenes, carbon nanotubes, or graphene. Composite materials prepared by dispersing such conductive particles in a matrix such as a polymer binder can also be used. The materials of the first electrode 131 and the second electrode 134 can be a single one or a combination of the above materials.

[0071] In some embodiments, at least one of the first electrode 131 or the second electrode 134 can be transparent. The transparent electrode can transmit light to be absorbed by the functional layer 133. In a semiconductor device used as a light-emitting device, the transparent electrode transmits the light emitted from the functional layer 133.

[0072] The first electrode 131 and the second electrode 134 collect electrons or holes generated in the functional layer 133. Therefore, it is beneficial to select materials suitable for collecting electrons or holes as the materials of the first electrode 131 and the second electrode 134. Materials with a high work function are suitable for collecting holes, and such materials include gold and ITO. Materials with a low work function are suitable for collecting electrons, and aluminum is an example of such a material.

[0073] There is no particular limitation on the thickness of the first electrode 131 and the second electrode 134, and it can be set according to, for example, conductivity and transparency. Typically, the thickness of the first electrode and the second electrode is about 10 nm to 10 μm.

[0074] Manufacturing process of the semiconductor device

[0075] Figures 4A to 4C is a schematic cross-sectional view showing a method of manufacturing a semiconductor device disclosed herein.

[0076] First, a process step of forming the wiring structure 106 will be described with reference to Figure 4A First, a substrate 100 is prepared. Next, the element isolation part 113 and the transistor 101 are formed in the substrate 100. Then, the wiring structure 106 is formed on the substrate 100. The wiring structure 106 can be formed of, for example, silicon oxide. Then, the first electrode 131 is formed directly above the via hole 111. After forming the first electrode 131, the insulating layer 112 may be formed again additionally. In this case, the insulating layer 112 and the first electrode are planarized so that the upper surface of the insulating layer 112 becomes flush with the upper surface of the first electrode 131. The planarization can be performed by etching or chemical mechanical polishing (CMP). Each layer described so far can be formed by a conventional semiconductor process.

[0077] Next, a process step of forming the intermediate layer 132 will be described with reference to Figure 4B The intermediate layer 132 is formed on the insulating layer 112 and the first electrode 131 by a vapor deposition method or a sputtering method, thereby completing the structure shown in Figure 4B For example, in order to form the titanium oxide intermediate layer 132, titanium oxide is deposited at a RF power of 500 W by using a TiO2 target and a sputtering apparatus. The introduced gas can be prepared by mixing argon flowing at a rate of 100 standard cubic centimeters (sccm) / minute with oxygen flowing at a rate of 5 sccm to 15 sccm. The pressure in the chamber can be 0.5 Pa.

[0078] Next, a process step of forming the functional layer 133 will be described with reference to Figure 4C After completing the structure described in Figure 4B the functional layer 133 is formed mainly by forming quantum dots. In the following description of forming the functional layer 133, a formation process of lead sulfide (PbS) quantum dots will be described by way of example. The specific process conditions described below are merely examples and do not limit the manufacturing process of the semiconductor device.

[0079] First, an exemplary synthesis process of PbS quantum dots will be described. 892 mg of lead oxide (PbO), 40 mL of octadecene, and 4 mL of oleic acid are put into a three-necked flask, and the flask is placed in an oil bath. The oil bath is heated to 90 °C. At this time, nitrogen is introduced into the three-necked flask at a flow rate of 0.5 mL / m to form a nitrogen atmosphere, thereby suppressing the oxidation of the quantum dots during the reaction. The solution under the slightly yellow reaction before being placed in the oil bath is stirred for 30 minutes or more until the solution becomes transparent.

[0080] Meanwhile, a solution of 20 mL of 1.9 mM bis(trimethylsilyl)sulfide in octadecene was prepared in a glove box under a nitrogen atmosphere. This solution served as the sulfur source. The sulfur source solution was rapidly added to the clear solution in a three-necked flask. One minute after adding the sulfur source, the three-necked flask was removed from the oil bath and cooled at room temperature for 2 hours. After the solution temperature reached room temperature, the next step, purification, was carried out. The solution after synthesis was black, indicating the production of lead sulfide (PbS) quantum dots with a surface protected by oleic acid.

[0081] Next, the purification step will be described. The dispersion of the obtained quantum dots in octadecene was transferred from the three-necked flask to a centrifuge tube. Acetone, which is a polar solvent, was added to the dispersion, and then the quantum dots could no longer remain dispersed in octadecene. In a centrifuge, the centrifuge tube containing acetone was centrifuged to precipitate the quantum dots. Centrifugation was carried out at, for example, 17000 rpm for 20 minutes.

[0082] Subsequently, after removing the centrifuge tube from the centrifuge, the clear supernatant acetone was discarded, and toluene, which is a non-polar solvent, was added to the quantum dots precipitated at the bottom of the centrifuge tube. Then, the centrifuge tube was shaken to redisperse the quantum dots in toluene. After adding acetone to the dispersion of the quantum dots in toluene, the quantum dot dispersion was centrifuged again at 15000 rpm for 5 minutes, thereby precipitating again.

[0083] The series of steps of precipitation with acetone and dispersion in toluene were repeated three times. Methanol, ethanol, or any other polar solvent can be used instead of acetone. However, a polar solvent that does not significantly affect the oleic acid protecting the quantum dots and does not cause the oleic acid to detach from the surface of the quantum dots is suitable.

[0084] Now, the preparation of the quantum dot liquid to be coated on the surface of the substrate to form a quantum dot film will be described. In the case of adding acetone to the toluene dispersion of the quantum dots, the quantum dots were precipitated by centrifugation. Then, the quantum dots were finally dispersed not in toluene but in octane, and the dispersion was adjusted to a quantum dot content of 80 mg / mL. This liquid was used as the quantum dot liquid to be coated in the subsequent step.

[0085] Now, the formation of the quantum dot film will be described. First, the quantum dot liquid was coated by spin-coating in such a way that the quantum dot liquid was dropped onto the center of the substrate placed in a spin coater. Spin-coating was carried out at, for example, 2500 rpm for 30 seconds. The obtained quantum dot film formed by spin-coating was an aggregate of quantum dots protected by oleic acid with a long molecular length, and thus, the distance between the quantum dots at each point was large. As a result, the photocarrier conductivity of the quantum dots was poor, and thus, the photoelectric conversion was poor. The obtained quantum dot film is referred to herein as an oleic acid-protected quantum dot film.

[0086] Quantum dot films protected by oleic acid are poor in photoelectric conversion and it is known to replace the molecules coordinated with the quantum dots. More specifically, a substance with a shorter molecular length than oleic acid is used to replace oleic acid. Hereinafter, this replacement is referred to as ligand exchange, and in some cases, the substance used for ligand exchange can be simply referred to as a ligand. In addition, the solution used for ligand exchange can be called a ligand solution. The embodiments described herein use 1,3-benzenedithiol (1,3-BDT) or 4-mercaptobenzoic acid (4-MBA) as organic ligands. The functional group of 1,3-benzenedithiol is only a thiol group, while 4-MBA has a thiol group and a carboxyl group. The ligand solution for ligand exchange can be a 3 mM solution of 1,3-BDT in acetonitrile or a 10 mM solution of 4-MBA in methanol. After ligand exchange using such organic ligands, a halogen (fluorine, chlorine, bromine, or iodine) can be added as an inorganic ligand. If iodine is added, for example, a 10 mM solution of lead iodide in N,N-dimethylformamide can be used. The halogen added as an inorganic ligand coordinates to the lead or sulfur defect sites on the surface of the quantum dots that are difficult to passivate only by organic ligands due to steric hindrance, thereby enabling passivation.

[0087] For ligand exchange, the above ligand solution is coated on the oleic acid-protected quantum dot film formed on the substrate. More specifically, the ligand solution is coated on the entire surface of the oleic acid-protected quantum dot film for a ligand exchange reaction for a predetermined time. In the ligand exchange reaction using 1,3-BDT or 4-MBA, the reaction time can be 30 seconds. However, the reaction time can be appropriately set according to, for example, the concentration of the ligand solution. After the reaction for a predetermined time, the substrate is rotated at 200 rpm for 60 seconds to remove the remaining ligand solution from the substrate. Then, the substrate is rinsed with acetonitrile or methanol, which is the solvent for dissolving the ligand, to remove the excess ligand remaining at the quantum dots. In addition, the substrate is rinsed with octane to remove the oleic acid detached from the quantum dots.

[0088] Another layer of oleic acid-protected quantum dot film can be further formed on the ligand-exchanged quantum dot film for ligand exchange and then rinsed. This series of steps can be repeated multiple times to form a multi-layer quantum dot film. The 1,3-BDT or 4-MBA quantum dot film structure with a predetermined thickness thus formed can be used as the functional layer 133. When forming such a functional layer 133, some ligand substances can be used such that the functional layer 133 can be composed of quantum dot films using different ligands. For example, the functional layer can be formed by forming one or more 1,3-BDT quantum dot films as the functional layers 133A and 133B and one or more 4-MBA quantum dot films as the functional layer 133C. In the semiconductor devices disclosed herein, image lag and photocurrent fluctuations can be reduced by appropriately designing the internal layers of the functional layer.

[0089] Subsequently, a second electrode 134 is formed. As described above, an electron blocking layer can be formed between the functional layer 133 and the second electrode 134. In one embodiment, the electron blocking layer can be formed of molybdenum oxide by chemical vapor deposition. Then, an insulating layer 136, a color filter layer 137, a planarization layer 138, and a microlens layer 139 are sequentially formed. These layers can be formed in a conventional semiconductor process, and thus their description is omitted. Therefore, the semiconductor device described above can be produced. Figure 2A the semiconductor device described in

[0090] Through the above process, oleic acid molecules of the atoms bonded to the surface of the nanoparticles in the oleic acid-protected quantum dot film are detached and replaced with predetermined ligand molecules. Thus, a 1,3-BDT or 4-MBA quantum dot film is formed. The thickness of the 1,3-BDT or 4-MBA quantum dot film after ligand exchange is 40 nm to 60 nm. After ligand exchange using an organic ligand, a halogen can be added as an inorganic ligand. For example, a lead iodide solution can be used to add iodine as the halogen. The reaction time for adding iodine can be 3 minutes. The reaction time can be changed according to conditions. Ligand exchange can be performed using only an inorganic ligand without using any organic ligand.

[0091] Display device using the semiconductor device

[0092] A semiconductor device according to an embodiment of the present disclosure can be used in a display device. The display device includes a light-emitting element having a functional layer disclosed herein. The light-emitting element is connected to an active element such as a transistor for controlling the light emission time and light emission brightness.

[0093] Figures 5A to 5D The use of a display device according to the present disclosure is shown. Figure 5A is a schematic view of an imaging device including a display device according to an embodiment of the present disclosure. The imaging device 300 can include a viewfinder 301, a rear display 302, an operation unit 303, and a housing 304. The viewfinder 301 can include a display device according to an embodiment of the present disclosure. In this case, the display device can display not only the captured image but also environmental information, imaging instructions, etc. The environmental information can include, for example, the intensity and direction of external light, the moving speed of the subject to be photographed, and the possibility of the subject being blocked by an obstacle. In one embodiment, the display device can be used in the rear display 302.

[0094] The imaging device 300 includes an optical system (not shown). The optical system includes a plurality of lenses and forms an image on an imaging element in a housing 304. The focus can be adjusted by adjusting the relative positions of the plurality of lenses. This can be performed automatically. The imaging device may be referred to as a photoelectric conversion device. The photoelectric conversion device may form an image not by forming images one by one, but by detecting the difference from a previous image or by cutting out one or more images from an image that is always recorded.

[0095] Figure 5B FIG. 4 is a schematic diagram of an electronic device including a display device according to an embodiment of the present disclosure. The electronic device 307 includes a display unit 305, an operation unit 308, and a housing 306. The housing 306 includes a circuit, a printed circuit board having the circuit, a battery, and a communication unit. The operation unit 308 may be a button or a touch panel responsive unit. The responsive unit may generate or receive ultrasonic waves or the like for biometric authentication using a fingerprint or the like. The operation unit 308 may have a biometric authentication function to identify a fingerprint and unlock. An electronic device including a communication unit may be referred to as a communication device. The electronic device may further include a lens and an imaging element, thereby functioning as a camera and other functions. An image captured by functioning as a camera is displayed on the display unit 305. Such an electronic device may be a smart phone, a mobile PC, or the like.

[0096] Figure 5C FIG. 8 is a schematic diagram of a display device according to an embodiment of the present disclosure. Figure 5C A display device such as a TV monitor or a PC monitor is described. The display device 309 includes a frame 312 and a display unit 310. The display unit 310 may include a light-emitting device according to an embodiment of the present disclosure.

[0097] The display unit further includes a base 311 that supports the frame 312 and the display unit 310. The base 311 is not limited to Figure 5C the form described in FIG. The lower side of the frame 312 may be used as the base, or the display unit may be a wall-mounted type or a roll-up type without using the base 311.

[0098] The frame 312 and the display unit 310 may be bent. The radius of curvature may be in the range of 5000 mm to 6000 mm.

[0099] Figure 5D FIG. 22 is a schematic diagram of a display device according to another embodiment of the present disclosure. Figure 5DThe display device 313 described in [description] is a foldable display device. The display device 313 includes a first display unit 317, a second display unit 314, and a housing 315, and has a folding line 316. Each of the first display unit 317 and the second display unit 314 may include a light-emitting device according to an embodiment of the present disclosure. The first display unit 317 and the second display unit 314 may form a one-piece continuous display without using a seam. The first display unit 317 and the second display unit 314 may be separated from each other along the folding line 316. The first display unit 317 and the second display unit 314 may display different images from each other, or a single image may be displayed across the first display unit and the second display unit.

[0100] Imaging system using the semiconductor device

[0101] Now, reference will be made to Figure 6A and Figure 6B to describe an imaging system and a moving body according to an embodiment.

[0102] Figure 6A and Figure 6B are block diagrams showing the structures of the imaging system and the moving body, respectively. Figure 6A An imaging system 400 for an in-vehicle camera is shown. The imaging system 400 includes an imaging device 410. The imaging device 410 may be an imaging device according to an embodiment of the present disclosure. The imaging system 400 further includes an image processor 412 as a device operable to process a plurality of image data obtained by the imaging device 410, and a parallax acquisition device 414 as a processor operable to calculate a parallax (phase difference between parallax images) from the plurality of image data obtained by the imaging device 410. In addition, the imaging system 400 includes a distance acquisition device 416 as a processor for calculating a distance to an object based on the calculated parallax, and a collision possibility determination device 418 as a processor for determining the possibility of a collision based on the calculated distance. The parallax acquisition device 414 and the distance acquisition device 416 are merely examples of information acquisition devices operable to obtain information such as distance data to an object. The distance data includes parallax, defocus value, and distance to an object. The collision possibility determination device 418 may determine the possibility of a collision by using any such distance data. The above-described processors may be implemented by dedicated hardware or by general-purpose software available for calculation based on hardware modules. Optionally, the processors may be implemented by an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit), etc. or a combination thereof.

[0103] The imaging system 400 is connected to the vehicle information acquisition device 420, enabling the system to receive vehicle information including vehicle speed, yaw rate, and steering angle. The imaging system 400 is also connected to the vehicle ECU (Electronic Control Unit) 430 that outputs a control signal based on the determination result of the collision possibility determination device 418 to generate a braking force for the vehicle. Therefore, the ECU 430 is a controller to control the moving body based on the distance data. The imaging system 400 is also connected to the alarm device 440 that issues a warning or alert to the driver based on the determination result of the collision possibility determination device 418. For example, if the collision possibility determination device 418 determines a high collision possibility, the vehicle ECU 430 controls the vehicle to brake, release the accelerator, and reduce the engine output, thereby avoiding collision and reducing damage. The alarm device 440 warns the driver, for example, by issuing an alarm, displaying alarm information on the screen of an automotive navigation system, or vibrating the seatbelt or the steering wheel.

[0104] In one disclosed embodiment, the imaging system 400 captures the surroundings of the vehicle, for example, the front or the rear. Figure 6B An imaging system 400 that captures the front of the vehicle (imaging range 450) is shown. The vehicle information acquisition device 420 commands the imaging system 400 to perform the capture. By using the imaging device according to one embodiment of the present disclosure as the imaging device 410, the imaging system 400 of the present disclosure can improve the accuracy of distance measurement.

[0105] In the shown embodiment, the imaging system disclosed herein controls the vehicle to avoid collision with other vehicles. However, in another embodiment, the imaging system can control autonomous driving by following other vehicles or driving autonomously so as not to leave the lane. The imaging system can also be used in other moving bodies (transport devices) such as ships, aircraft, and industrial robots. Examples of the moving devices used in such moving bodies (transport devices) include engines, electric motors, wheels, and propellers. The imaging system can be used not only in moving bodies but also in devices or systems that can identify objects in a wide range of fields such as, for example, the Intelligent Transport System (ITS).

[0106] The photoelectric conversion device according to one embodiment can be used in an imaging device or an imaging system. The following will refer to Figure 7 Describe the imaging system.

[0107] Figure 7 is a schematic block diagram showing the structure of an imaging system according to one embodiment.

[0108] The photoelectric conversion device disclosed in this text can be used in various imaging systems. Such imaging systems include, but are not limited to, digital cameras, digital video cameras, surveillance cameras, copiers, fax machines, mobile phones, in-vehicle cameras, observation satellites, and medical cameras. A camera module including an optical system such as a lens and a photoelectric conversion device is also an imaging system. Figure 7 A block diagram of a digital camera, which is an example of an imaging system, is shown.

[0109] The digital camera, or imaging system 500, includes a photoelectric conversion device 200, an imaging optical system 502, a central processing unit (CPU) 510, a lens controller 512, an imaging device controller 514, an image processor 516, an aperture / shutter controller 518, a display unit 520, an operation switch 522, and a recording medium 524.

[0110] The imaging optical system 502 is designed to form an optical image of the subject and includes a lens and an aperture 504. The aperture 504 has an opening (aperture) whose diameter can be changed to adjust the amount of light during shooting, and additionally functions as a shutter to adjust the exposure time when shooting a still image. The lens and the aperture 504 are held so as to be able to expand and contract in the direction of the optical axis, and the interlocking of such a lens and aperture enables variable magnification (zoom) and focus adjustment. The imaging optical system 502 can be integrated into the imaging system or can be an imaging lens unit that can be attached to the imaging system.

[0111] The photoelectric conversion device 200 is arranged such that the imaging surface of the imaging optical system 502 is located in the image space of the optical system. The photoelectric conversion device 200, which is a semiconductor device serving as a photoelectric conversion device according to an embodiment of the present disclosure, includes a complementary metal oxide semiconductor (CMOS) sensor (pixel portion) and a peripheral circuit (peripheral circuit region). The photoelectric conversion device 200 includes pixels in a two-dimensional configuration having a plurality of photoelectric conversion portions and color filters arranged corresponding to the pixels, thereby constituting a two-dimensional single-plate color sensor. The photoelectric conversion device 200 photoelectrically converts the optical image of the subject formed by the imaging optical system 502 into an image signal or a focus detection signal and outputs the converted signal.

[0112] The lens controller 512 controls the telescopic interlocking of the lens of the imaging optical system 502 to change the magnification or adjust the focus, and includes a circuit or a processor configured to achieve this function. The aperture / shutter controller 518 changes the opening diameter (variable opening value) of the aperture 504 to adjust the amount of imaging light, and includes a circuit or a processor configured to achieve this function.

[0113] The CPU 510, which serves as a controller in the camera, controls the camera in various aspects and includes a processor, a read-only memory (ROM), a random-access memory (RAM), an (analog-to-digital) A / D converter, a D / A (digital-to-analog) converter, and a communication interface circuit. The CPU 510 controls the operation of the devices or the operations of the respective parts within the camera according to the computer programs stored in the ROM and the like, and executes a series of imaging operations, such as an autofocus operation including detection of the focusing state (focus detection) of the imaging optical system 502, imaging, image processing, and recording. The CPU 510 also functions as a signal processor.

[0114] The imaging device controller 514 controls the operation of the photoelectric conversion device 200, and further, A / D-converts the signal output from the photoelectric conversion device 200 and transmits the converted signal to the CPU 510. The imaging device controller 514 includes circuits or controllers configured to achieve this function. The A / D conversion may be a function of the photoelectric conversion device 200. The image processor 516 performs image processing such as γ conversion or color interpolation on the A / D-converted signal, thereby generating an image signal. The image processor 516 includes circuits or controllers configured to achieve this function. The display unit 520 is, for example, a liquid crystal display (LCD) device and displays information related to the shooting mode of the camera, a preview image before shooting, an inspection image after shooting, and the focusing state when the focus is detected. The operation switch 522 includes a power switch, a release (shooting trigger) switch, a zoom switch, and a shooting mode selection switch. The recording medium 524 on which the captured pictures or images are recorded may be included in the imaging system or may be a removable memory card.

[0115] The imaging system 500 using the photoelectric conversion device 200 according to one embodiment of the present disclosure can achieve high performance.

[0116] The photoelectric conversion device may be a front-illuminated type or a back-illuminated type. The photoelectric conversion device may have a multilayer structure (stacking of chips) including a first semiconductor chip having a plurality of photoelectric conversion parts and a second semiconductor chip having a peripheral circuit. The peripheral circuit of the second semiconductor chip may be a column circuit corresponding to the columns of the pixel arrangement of the first semiconductor chip. Alternatively, the peripheral circuit of the second semiconductor chip may be a matrix circuit corresponding to the pixels or pixel blocks of the first semiconductor chip. The first semiconductor chip and the second semiconductor chip may be coupled by using through-silicon vias (TSVs), wiring using conductors such as copper wires, using micro-bumps, or wire bonding.

[0117] The above-disclosed embodiments are merely some embodiments of the present disclosure, and the scope of the present disclosure is not limited to the disclosed embodiments.

[0118] Examples

[0119] The subject matter of the present disclosure will be further described with reference to embodiments. In the embodiments, an element having a multilayer structure using some ligand materials is evaluated to show that a specific multilayer structure is effective in reducing image lag and photocurrent fluctuation.

[0120] Evaluation of image lag and photocurrent fluctuation

[0121] Image lag is a phenomenon in which charges are not completely transferred through one scan and remain until the next scan. In this case, the device cannot respond to a sudden change in the incident light intensity, thereby forming a picture that looks like a trailing in actual video shooting. Image lag should be reduced. Photocurrent fluctuation is a phenomenon in which the photocurrent fluctuates even when the incident light intensity remains constant. Even though the light intensity is constant during actual image shooting, a bright picture is formed. Photocurrent fluctuation should be minimized. Image lag and photocurrent fluctuation can be evaluated by measuring the transient current response of the photoelectric conversion element between the first electrode 131 and the second electrode 134 in the image sensor in the bright state irradiated with light and in the dark state without light irradiation.

[0122] Figure 8A and Figure 8B are measurement diagrams of the residual of electrons and the fluctuation of current generated in the photoelectric conversion element according to one embodiment, respectively. Figure 8A represents the measurement in the case of using MBA as a ligand in the layer corresponding to the functional layer 133C. Figure 8B represents the measurement in the case of using a ligand other than MBA in the layer corresponding to the functional layer 133C.

[0123] The measurement is evaluated as follows. The initial dark current when the element is energized for a certain time until the dark current becomes stable is represented by A. Then, the element is irradiated with light. The photocurrent after a predetermined time from the irradiation is represented by B. Then, the light is turned off. The dark current one minute after the light is turned off is represented by C, and the current immediately after the light irradiation starts is represented by D. When measuring the transient current response, a voltage of 4.8 V is applied.

[0124] In the specification disclosed herein, image lag is quantified by the following formula (1):

[0125] Image lag (%) = |(C - A)| / |(B - A)| (1)

[0126] In the specification disclosed herein, photocurrent fluctuation is quantified by the following formula (2):

[0127] Photocurrent fluctuation (%) = D / B (2)

[0128] In Figure 8A and Figure 8BIn the current difference shown is equivalent to the observed image lag. There are two types of image lag: "whitening" that occurs when the dark current after the end of light irradiation is higher than the initial dark current, as shown in Figure 8A ; and "blackening" that occurs when the dark current after the end of light irradiation is lower than the initial dark current, as shown in Figure 8B .

[0129] The materials of the electrodes and ligands and the thicknesses and compositions of the respective layers in the sample element described below are merely examples, and the present disclosure is not limited to the disclosed embodiments. The first electrode 131 is made of titanium nitride with a thickness of 60 nm. The intermediate layer 132 is made of titanium oxide with a thickness of 50 nm and serves as an adhesion layer and a hole blocking layer. The functional layer 133 is composed of PbS quantum dots. The average particle size of the quantum dots is about 3.0 nm and the band gap energy is about 1.34 eV. A lead iodide solution is used for adding halogens. The second electrode 134 is a transparent ITO electrode with a thickness of 40 nm. The sample element is prepared as described above. The transient response of each element is measured as described above. For the measurement, the element is energized for 5 minutes in the state of turning off the light from the start of voltage application, and then irradiated with light for 4 minutes. After turning off the light again, the measurement is continued for 1 minute. The applied voltage is 4.8 V. For the applied voltage and the measured current, a semiconductor parameter analyzer 4156B manufactured by Agilent is used. For the light irradiation, a surface-emitting white LED TH-100X100SW manufactured by CCS Inc. is used.

[0130] Examples and comparative examples are shown together in the table. Sample elements of Examples 1 to 5 and Comparative Examples 1 to 5 are prepared under the same conditions except that the ligands shown in the table are used for the functional layer. Now, the symbols in the table will be described. The functional layer is formed to change the thickness and is treated with the changed ligands. EQE(500 nm) represents the external quantum efficiency (%) at 500 nm, which is a representative incident light wavelength in the visible light region. EQE(940 nm) represents the external quantum efficiency (%) at 940 nm, which is a representative incident light wavelength in the infrared light region. The number of dark electrons (60 °C) is represented by " / s·μm 2 ". The values shown in the table are the measured values obtained in independent trials under an applied voltage of 2 V. The image lag (%) and the photocurrent fluctuation (%) are defined as above. The number of dark electrons, the image lag, and the photocurrent fluctuation are evaluated according to the following criteria. The grades A > B > C indicate better evaluations in sequence.

[0131] Number of dark electrons

[0132] A: less than 5000 / s·μm 2

[0133] B: 5000 / s·μm2 to less than 10,000 / s·μm 2

[0134] C: 10,000 / s·μm 2 or more

[0135] Image lag

[0136] A: less than 0.01%

[0137] B: 0.01% to less than 0.1%

[0138] C: 0.1% or more

[0139] Photocurrent fluctuation

[0140] A: less than 5%

[0141] B: 5% to less than 10%

[0142] C: 10% or more

[0143] Table

[0144]

[0145] Functional layers 133A, 133B, and 133C in the table are formed to change the thickness and are treated with the changed ligand substances. For the ligand substances shown in the table, 1,3-BDT represents 1,3-benzenedithiol; 4-MBA represents 4-mercaptobenzoic acid; 3-MBA represents 3-mercaptobenzoic acid; 2-MBA represents 2-mercaptobenzoic acid; MPA represents 3-mercaptopropionic acid; and PbI2 represents lead iodide. The molecular structures of the organic substances are shown below. For example, in the case of Comparative Example 1, four quantum dot films each having a thickness of about 50 nm are formed into a multilayer structure, thereby constituting a 200-nm-thick functional layer 133. "None" in the columns of functional layer 133A and functional layer 133C means that the element does not have a quantum dot film different from functional layer 133B and corresponding to functional layer 133A or 133C. Therefore, the functional layer of Comparative Example 5 is composed of only one functional layer having one ligand, and functional layer 133B is in contact with the intermediate layer and the electrode.

[0146]

[0147] In Comparative Example 1, the functional layer is composed of only one functional layer 133 which is a quantum dot film using 1,3-BDT and PbI2 as ligands. As a result, neither image lag nor photocurrent fluctuation is sufficiently reduced.

[0148] In Comparative Example 2, the functional layer is constituted by a multilayer structure composed of a functional layer 133B which is a quantum dot film using 1,3-BDT and PbI2 as ligands and a functional layer 133A which is a quantum dot film using 4-MBA and PbI2 as ligands. The other layers are the same as those in Comparative Example 1. Although the evaluation in terms of the number of dark electrons is good, neither the image lag nor the photocurrent fluctuation is sufficiently reduced.

[0149] The photoelectric conversion elements of Comparative Examples 3 and 4 use the quantum dots described in U.S. Patent Application Publication No. 2016 / 0133463. In the production processes of the photoelectric conversion elements of Comparative Examples 3 and 4, annealing is not performed from the viewpoint of stability.

[0150] In Comparative Example 3, the functional layer is constituted by quantum dots having only PbI2 ligands. The other layers are the same as those in Comparative Example 1. The quantum dots having PbI2 ligands do not have an organic ligand set. As a result, although the evaluation in terms of the image lag is quite good, the photocurrent fluctuation is not sufficiently reduced.

[0151] In Comparative Example 4, the functional layer is constituted by a multilayer structure composed of a functional layer 133B and a functional layer 133C, the functional layer 133B is composed of some quantum dot films using PbI2, and the functional layer 133C is composed of some quantum dot films using MPA. The photoelectric conversion element of Comparative Example 4 is not satisfactory in terms of the number of dark electrons, but shows a high EQE of 66% at 500 nm and 43% at 940 nm. However, neither the image lag nor the photocurrent fluctuation is sufficiently reduced.

[0152] In Comparative Example 5, the functional layer is constituted only by a single functional layer 133 composed of some quantum dot films using 4-MBA. The other layers are the same as those in Comparative Example 1. Since the photoelectric conversion element uses 4-MBA as a ligand substance containing a benzene ring and having a high boiling point, the number of dark electrons is sufficiently reduced, but the EQE is low: 3% at 500 nm and 4% at 940 nm. In addition, neither the image lag nor the photocurrent fluctuation is sufficiently reduced.

[0153] In Example 1, the functional layer is constituted by a multilayer structure composed of a functional layer 133B and a functional layer 133C, the functional layer 133B is composed of some quantum dot films using 1,3-BDT and PbI2 as ligands, and the functional layer 133C is composed of quantum dot films using 4-MBA and PbI2 as ligands. Even after annealing at 170 °C for one hour, the obtained element shows an EQE of 70% at 500 nm and 29% at 940 nm, and the rating of the number of dark electrons at 60 °C is A. Therefore, the photoelectric conversion performance is high. In addition, the evaluations in terms of the image lag and the photocurrent fluctuation are higher than those of any of Comparative Examples 1 to 5.

[0154] The structure of Example 1 is different from that of Comparative Example 2 in terms of the position of the functional layer using 4-MBA as a ligand. More specifically, in Example 1, the layer using 4-MBA is disposed between the functional layer 133B and the cathode. In contrast, in Comparative Example 2, the layer using 4-MBA is disposed between the anode and the functional layer 133B. Therefore, it is beneficial that the functional layer C using 4-MBA is disposed between the functional layer 133B and the cathode. The functional layer B can be a photoelectric conversion layer mainly for photoelectric conversion. The photoelectric conversion efficiency of the functional layer B can be higher than those of the functional layers A and C.

[0155] Examples 2 and 3 use 3-MBA and 2-MBA instead of 4-MBA, respectively. 3-MBA and 2-MBA are each different from 4-MBA in terms of the position of the benzoic acid substituted by a thiol.

[0156] In Example 2, the functional layer is composed of a multilayer structure formed by the functional layer 133B and the functional layer 133C. The functional layer 133B is composed of some quantum dot films using 1,3-BDT and PbI2 as ligands, and the functional layer 133C is composed of quantum dot films using 3-MBA and PbI2 as ligands. The other layers are the same as those in Example 1. Even after annealing at 170 °C for one hour, the resulting device shows an EQE of 42% at 500 nm and 14% at 940 nm, and a dark electron number rating of A at 60 °C. In addition, the photocurrent fluctuation is not sufficiently reduced, and the evaluation in terms of image lag is high.

[0157] In Example 3, the functional layer is composed of a multilayer structure formed by the functional layer 133B and the functional layer 133C. The functional layer 133B is composed of some quantum dot films using 1,3-BDT and PbI2 as ligands, and the functional layer 133C is composed of quantum dot films using 2-MBA and PbI2 as ligands. The other layers are the same as those in Example 1. Even after annealing at 170 °C for one hour, the resulting device shows an EQE of 38% at 500 nm and 17% at 940 nm, and a dark electron number rating of A at 60 °C. In addition, the photocurrent fluctuation is not sufficiently reduced, and the evaluation in terms of image lag is high.

[0158] The results of Examples 1 to 3 show that in the functional layer 133C, the presence of MBA having an aromatic ring bonded to a thiol group and a carboxyl group reduces image lag, regardless of the substitution position.

[0159] In contrast, in Comparative Example 4 where the functional layer 133C uses MPA having a thiol group and a carboxyl group but no aromatic ring, image lag is not sufficiently reduced. This indicates that an aromatic compound having a thiol group and a carboxyl group is effective in reducing image lag. In particular, 4-MBA is effective in reducing both image lag and photocurrent fluctuations, and thus is useful as a material for a photoelectric conversion element.

[0160] Furthermore, photocurrent fluctuations were compared among Examples 1 to 3. MBA has a thiol group and a carboxyl group that coordinate with Pb at the surface of the quantum dots. 4-MBA is para-substituted by a thiol group and a carboxyl group; and 3-MBA and 2-MBA are meta- and ortho-substituted, respectively. Therefore, 4-MBA can crosslink between quantum dots, while 3-MBA and 2-MBA are more likely to increase the distance between quantum dots than 4-MBA. The greater the distance between quantum dots, the lower the carrier transport characteristics. If the functional layer 133B uses 1,3-BDT and the functional layer 133C uses 3-MBA or 2-MBA, holes may accumulate at the interface between these functional layers, hindering current based on the electrons generated in the functional layers. This may be the reason for the reduction in photocurrent during irradiation. Therefore, an organic ligand having an aromatic ring para-substituted by a thiol group and a carboxyl group is more beneficial.

[0161] Sample elements of Examples 4 and 5 were prepared in the same manner as in Example 1, except that the thicknesses of the functional layer 133B using 1,3-BDT and PbI2 and the functional layer 133C using 4-MBA and PbI2 were changed. In Example 1, the total thickness of the 150-nm-thick functional layer 133B and the 50-nm-thick functional layer 133C was 200 nm. In contrast, the total thickness of the functional layers in Examples 4 and 5 was 400 nm. Since the photoelectric conversion layer, or the functional layer 133, is disposed between the first electrode and the second electrode, the total thickness of the functional layer corresponds to the distance between the electrodes. If a boundary layer such as the intermediate layer 132 or an electron blocking layer (not shown) is provided between the electrode and the photoelectric conversion layer, the total thickness of the photoelectric conversion layer 133 is composed of subtracting the thickness of such a boundary layer from the distance between the electrodes.

[0162] The boundary between each layer can be determined by compositional analysis in the thickness direction using, for example, cross-sectional transmission electron microscopy (cross-sectional TEM) or time-of-flight secondary ion mass spectrometry (TOF-SIMS). The percentage of the functional layer 133C relative to the total thickness calculated by (thickness of the functional layer 133C) / (total thickness) × 100 represents the proportion of the functional layer 133C occupying the element structure from the second electrode toward the first electrode.

[0163] In Example 4, the percentage of the functional layer 133C was 12.5%. Even after annealing at 170 °C for one hour, the resulting device showed an EQE of 73% at 500 nm and 44% at 940 nm, and a dark electron number rating of A at 60 °C. Additionally, both image lag and photocurrent fluctuations were sufficiently reduced. The percentage of the functional layer 133C in Example 4 was as small as 12.5%, which is less than 25% in Example 1. However, the device of Example 4 produced substantially the same effects in terms of image lag and photocurrent fluctuations. Furthermore, the EQE at 940 nm was improved. This is because light absorption was increased by increasing the thickness of the functional layer 133B that is mainly involved in light absorption for photoelectric conversion.

[0164] In Example 5, the percentage of the functional layer 133C was 37.5%. Even after annealing at 170 °C for one hour, the resulting device showed an EQE of 53% at 500 nm and 33% at 940 nm, and a dark electron number rating of A at 60 °C. Although image lag was sufficiently reduced, photocurrent fluctuations were not much reduced compared to Examples 1 and 4. This is because the thickness of the functional layer B was smaller and the thickness of the functional layer C was larger compared to Example 4.

[0165] The results of Example 1 (percentage of the thickness of the functional layer 133C: 25%), Example 4 (percentage of the thickness of the functional layer 133C: 12.5%), and Example 5 (percentage of the functional layer 133C: 37.5%) show that the presence of the functional layer 133C using 4-MBA between the functional layer B and the cathode results in a reduction of image lag. The results indicate that when the thickness of the functional layer using MBA is 25% or less of the total thickness of the functional layer, the device can exhibit high current characteristics as well as reduced image lag. The functional layer 133C at least includes a quantum dot film coordinated with 4-MBA and has a thickness as large as the quantum dot particle size of 3 nm, accounting for 1.5% of the total thickness. In other words, in an embodiment where the second functional layer is provided between the cathode and the first functional layer with high photoelectric conversion efficiency, the thickness of the second functional layer is 1.5% to 25% with respect to the distance between the electrodes.

[0166] As described above, the present disclosure can provide a semiconductor device having a stable current when irradiated with light.

[0167] Although the present disclosure has been described with reference to exemplary embodiments, it should be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications as well as equivalent structures and functions.

Claims

1. A semiconductor device, characterized in that, It includes: An anode; A cathode; A first functional layer between the anode and the cathode, the first functional layer containing first quantum dots having a first ligand; And A second functional layer between the first functional layer and the cathode, the second functional layer containing second quantum dots having a second ligand different from the first ligand, the second ligand being an aromatic compound having a sulfur bond and an ester bond.

2. A semiconductor device, characterized in that, It includes: An anode; A cathode; A first functional layer between the anode and the cathode, the first functional layer containing first quantum dots having a first ligand; And A second functional layer between the first functional layer and the cathode, the second functional layer containing second quantum dots having a second ligand different from the first ligand, the second ligand being an aromatic compound having a sulfur bond and an ester bond, wherein the difference between the lowest energy of the conduction band of the second quantum dots and the triplet excitation energy of the second ligand is less than the difference between the lowest energy of the conduction band of the first quantum dots and the triplet excitation energy of the first ligand.

3. The semiconductor device according to claim 2, wherein the lowest energy of the conduction band of the second quantum dots is higher than the triplet excitation energy of the second ligand.

4. The semiconductor device according to claim 2, wherein the difference between the lowest energy of the conduction band of the second quantum dots and the triplet excitation energy of the second ligand is 0.8 eV or less.

5. The semiconductor device according to claim 2, wherein the difference between the lowest energy of the conduction band of the second quantum dots and the triplet excitation energy of the second ligand is 0.3 eV or less.

6. A semiconductor device, characterized in that, It includes: An anode; A cathode; A first functional layer between the anode and the cathode, the first functional layer containing first quantum dots having a first ligand; And A second functional layer between the first functional layer and the cathode, the second functional layer containing second quantum dots having a second ligand different from the first ligand, the second ligand being an aromatic compound having a sulfur bond and an ester bond, wherein the difference between the lowest energy of the conduction band of the second quantum dots and the singlet excitation energy of the second ligand is less than the difference between the lowest energy of the conduction band of the first quantum dots and the singlet excitation energy of the first ligand.

7. The semiconductor device according to claim 6, wherein the lowest energy of the conduction band of the second quantum dots is higher than the singlet excitation energy of the second ligand.

8. The semiconductor device according to claim 6, wherein the difference between the lowest energy of the conduction band of the second quantum dots and the singlet excitation energy of the second ligand is 0.3 eV or less.

9. The semiconductor device according to any one of claims 1 to 8, wherein the photoelectric conversion efficiency of the first functional layer is higher than that of the second functional layer.

10. The semiconductor device according to any one of claims 1 to 8, wherein the thickness of the second functional layer is 25% or less relative to the distance between the anode and the cathode.

11. The semiconductor device according to any one of claims 1 to 8, wherein the thickness of the second functional layer is 1.5% to 25% relative to the distance between the anode and the cathode.

12. The semiconductor device according to any one of claims 1 to 8, wherein the second ligand of the second quantum dots included in the second functional layer is selected from the group consisting of 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, and 2-mercaptobenzoic acid.

13. The semiconductor device according to any one of claims 1 to 8, wherein the first functional layer and the second functional layer are each a quantum dot film composed of colloidal quantum dots.

14. The semiconductor device according to any one of claims 1 to 8, wherein at least one of the first functional layer and the second functional layer contains a halogen selected from the group consisting of iodine, chlorine, bromine, and fluorine.

15. The semiconductor device according to any one of claims 1 to 8, wherein the first functional layer and the second functional layer serve as a photoelectric conversion layer.

16. The semiconductor device according to any one of claims 1 to 8, wherein the first quantum dots and the second quantum dots of the first functional layer and the second functional layer contain PbS or PbSe.

17. A display device, characterized in that, It includes: The semiconductor device according to any one of claims 1 to 16; and An active element coupled to the semiconductor device, the active element being operable to control the light emission brightness of the semiconductor device.

18. An imaging system, characterized in that, It includes: The semiconductor device according to any one of claims 1 to 16; and A processor operable to process a signal output from the semiconductor device.

19. A moving body, characterized in that, It includes: The semiconductor device according to any one of claims 1 to 16; A mobile device; A processor operable to obtain information from a signal output from the semiconductor device; and A controller operable to control the mobile device according to the information.

Images