Hod device and applications thereof

Abstract

Disclosed are a HOD device and application thereof. The HOD device comprises an anode, a cathode, and a hole injection layer, a hole transport layer and an electron blocking layer arranged between the anode and the cathode, the hole transport layer is formed by a first organic material, and a specific p-type material is doped into the first organic material or a second organic material to form the hole injection layer. The HOD device realizes an ohmic contact between the anode and the organic material, avoids a potential barrier between film layers, and can obtain more accurate results and more truly reflect the hole mobility of the organic material when the hole mobility of the first organic material is measured by using the HOD device.

Description

Technical Field

[0001] This invention relates to a HOD device and a method for measuring hole mobility in organic materials using the device. More particularly, it relates to a method for measuring hole mobility in deep-level organic materials. Background Technology

[0002] Organic semiconductor materials have attracted widespread attention in recent years due to their unique physical and chemical properties, and their applications have expanded to many areas such as displays, lighting, solar cells, transistors, and sensors. Realizing these applications requires a key focus on the carrier mobility of organic semiconductor materials, i.e., the migration rate of charge carriers within the material under a given electric field. This mobility determines the power consumption of the device and, consequently, the application potential of devices constructed from organic semiconductor materials. Charge carriers are generally divided into two types: holes and electrons. In organic semiconductor materials, the mobility of holes is typically much higher than that of electrons. Therefore, the hole mobility is one of the most crucial indicators for evaluating the performance of organic semiconductor materials. For example, in organic light-emitting diodes (OLEDs), selecting organic materials with high hole mobility is beneficial for improving the device's charge injection capability, reducing voltage drop in the transport material, and lowering device power consumption. Simultaneously, if the hole mobility of the hole transport material in the OLED device can be known, electron transport materials with matching electron mobility can be selected to achieve a balance between the two types of charge carriers, thereby obtaining superior device performance. Therefore, the mobility of organic semiconductor materials, especially hole mobility, is one of the important parameters for evaluating organic materials, and it can have a significant impact on device performance. Thus, accurate and reproducible measurement of the mobility of organic semiconductor materials, especially hole mobility, is of great significance.

[0003] The most common method for measuring carrier mobility is the space charge limited current (SCLC) method. Under the influence of the space charge effect, the current flowing through the space charge region is primarily drift current. The electric field determining the drift current is mainly generated by the carriers; therefore, carrier charge, electric field, and current are mutually restrictive. Specifically, the drift current of carriers flowing through the space charge region is limited by the corresponding space charge. Since the current has an exponential relationship with the injection barrier, the measured current is very sensitive to changes in the barrier height. When the barrier height is close to zero, the contact between the electrode and the organic interface can be considered an ohmic contact, which is the space charge limited current region (i.e., the SCLC conduction region). The square root of the current density is linearly related to the voltage, and the carrier mobility can be calculated using the formula. If the electrode and the organic material interface do not form an ohmic contact, there is a certain resistance, which is the injection limited current region (i.e., the ohmic conduction region). In this case, the square root of the current density is not linearly related to the voltage and cannot be used to calculate the carrier mobility.

[0004] SCLC is a simple and convenient method, requiring only a relatively thin sample thickness and a basic experimental setup. Generally, SCLC is implemented by fabricating a hole-only device (HOD device). By measuring the JV data of the HOD device, a linearly varying JV that conforms to the SCLC model is fitted. 1 / 2 The -V relationship curve is used to calculate the mobility of the organic material or organic layer. However, when applying this technique, it is crucial to ensure that a good ohmic contact is formed between the electrode and the organic interface. If an ohmic contact is not formed, as mentioned above, J-type defects will appear before entering the conductive region of the SCLC. 1 / 2 The -V nonlinear relationship in the ohmic conductivity region requires a significantly increased electric field to enter the SCLC region, which is usually far from the operating electric field of the material in practical device applications. Furthermore, even after entering the SCLC conductivity region under a large electric field, it is crucial to accurately locate the starting point of the SCLC conductivity region; otherwise, the calculated mobility will have a large error. However, due to the existence of the ohmic conductivity region, the transition curve between the two regions does not have a clear inflection point, making the determination of the boundary between the two regions highly subjective. This explains why different literature reports different mobility values ​​for the same organic material. Therefore, an ideal condition for measuring hole mobility using HOD devices is that the organic semiconductor material and the electrode have good ohmic contact, under which the measured J... 1 / 2 The -V curve does not have an ohmic conductivity region, but directly enters the linear SCLC conductivity region, so the hole mobility measured in this way is more objective and accurate.

[0005] To obtain accurate hole mobility measurements, in addition to ensuring good ohmic contact between the organic materials and electrodes in the HOD device, it is also necessary to minimize or even eliminate potential barriers between the organic layers within the device, such as the HOMO barrier between the hole injection layer and the test transport material layer. The presence of this barrier increases the voltage, resulting in a measured mobility lower than the intrinsic mobility of the material. The higher the barrier, the greater the difference between the calculated mobility and the intrinsic mobility. Conversely, if there is no barrier or the barrier is extremely small, the measured mobility value will generally be larger and closer to the intrinsic mobility of the material (because defects always exist between interfaces, the measurement result can only be made closer to the intrinsic mobility). The best approach to balance ohmic contact and zero barrier is to use the test material as the host material for hole transport in the hole injection layer (thus eliminating the HOMO barrier between the hole injection layer and the test material) and incorporate p-type conductive materials to achieve ohmic contact. However, for measuring hole transport materials with deeper HOMO levels, achieving good ohmic contact with the electrode requires p-type conductive materials with even deeper LUMO levels. As the energy level of the material under test increases, the number of matching p-type conductive materials becomes increasingly scarce, or even impossible to obtain. Therefore, accurately measuring the hole mobility of deep-level materials is particularly challenging.

[0006] Patent CN106848060B discloses a single-hole device (HOD) using an asymmetric organic hole transport material. This device utilizes a self-developed hole transport material, and its hole mobility was tested using SCLC. MoO3 was used as both the hole injection layer and the electron blocking layer. However, the work function of transition metal oxides such as MoO3 is too high, creating a significant potential barrier between them and the electrode material, hindering the formation of a good ohmic contact. Therefore, the hole mobility of the single-hole device fabricated using MoO3 as the hole injection layer is not accurately measured. The literature Synthetic Metals 180 (2013) 79-84 and Applied Physics Letters, 96, 243310 2010 both reported the hole mobility of TPDI (5,10,15-triphenyl-5H-diindole[3,2-a:3',2'-c]carbazole) measured by SCLC. However, the hole injection layer material and the thickness of the organic layer used in the two literatures for the HOD device are different. They also did not balance the injection barrier between the hole injection layer and the anode, or the barrier between the hole injection material and the test material. This resulted in a large difference in the measured hole mobility, which could not reflect the true hole mobility.

[0007] The paper Semicond. Sci. Technol. 23 (2008) 055014 investigated the effect of different concentrations of p-type doped hole transport materials as hole injection layers on the performance of OLED devices. The study concluded that the device voltage decreased with increasing p-type conductive material doping concentration. Although they fabricated HOD devices and tested the JV characteristic curves, their purpose was to study the improvement of conductivity by p-type doping, qualitatively demonstrating that at a given voltage, conductivity improves with increasing doping concentration. This paper did not explore a method for measuring hole mobility, nor did it propose requirements for each layer of the HOD device.

[0008] In summary, while SCLC is a convenient and widely used method for measuring the mobility of organic materials, it suffers from significant measurement errors due to the contact barriers between the anode and the organic material, as well as the barriers between the hole injection layer and the tested organic material, especially for deep-level organic materials. It is difficult to find a suitable host or dopant material for hole transport to match the energy level, thus hindering the formation of a good ohmic contact. This results in inaccurate measurement of the mobility of the tested material. Therefore, designing a suitable HOD device to circumvent the contact barriers between film layers, enabling the formation of a good ohmic contact, and using this HOD device to more accurately and objectively measure the true mobility of organic semiconductor materials is of paramount importance. Summary of the Invention

[0009] This invention provides a hole-transporting device (HOD) and a method for measuring the hole mobility of deep-level organic materials using this device. In the HOD device, a first organic material is used to form a hole transport layer, and a suitable p-type dopant is selected and incorporated into either the first or second organic material to form the hole injection layer. A specific doping concentration of the p-type dopant is chosen to maximize the conductivity of the hole injection layer. This type of HOD device does not have an ohmic conductivity region. 1 / 2 -V changes linearly. Using this HOD device to measure the hole mobility of the first organic material, an ohmic contact between the anode and the organic material is achieved, avoiding or reducing the potential barrier between the hole injection layer and the first organic material, thus enabling a more accurate measurement of the hole mobility of the organic material.

[0010] According to one embodiment of the present invention, a HOD device is disclosed, which includes an anode, a cathode, and a hole injection layer, a hole transport layer and an electron blocking layer disposed between the anode and the cathode;

[0011] The hole transport layer is formed of the first organic material;

[0012] The hole injection layer is formed by doping a first doping material in a first organic material at a mass ratio of doping concentration x, or by doping a second doping material in a second organic material at a mass ratio of doping concentration x.

[0013] The HOMO level of the first organic material is HOMO1, the HOMO level of the second organic material is HOMO2, the LUMO level of the first doped material is LUMO1, and the LUMO level of the second doped material is LUMO2. HOMO1, HOMO2, LUMO1, and LUMO2 satisfy the following conditions:

[0014] HOMO1<5.0eV; 0≤HOMO2-HOMO1≤0.22eV; LUMO1-HOMO1≤0.20eV;

[0015] LUMO2–HOMO2≤0.20eV;

[0016] The doping concentration x can be any value that simultaneously satisfies the following conditions:

[0017] i. The doping concentration x is 1% to 60%;

[0018] ii. Make the electrical conductivity of the hole injection layer greater than 10 × 10⁻⁶. -3 S / m;

[0019] iii. After the doping concentration is increased to 1.2x to 1.5x, the change in the conductivity of the hole injection layer is no more than 30%.

[0020] According to one embodiment of the present invention, HOMO1 ≤ -5.2 eV.

[0021] According to one embodiment of the present invention, HOMO1 ≤ -5.3 eV.

[0022] According to one embodiment of the present invention, LUMO1-HOMO1≤0.15eV.

[0023] According to one embodiment of the present invention, 0 ≤ HOMO2 - HOMO1 ≤ 0.20 eV.

[0024] According to one embodiment of the present invention, a good ohmic contact can be formed between the anode and the hole injection layer.

[0025] According to one embodiment of the present invention, the doping concentration x is 5% to 50%.

[0026] According to one embodiment of the present invention, the doping concentration x is 10% to 50%.

[0027] According to one embodiment of the present invention, the doping concentration x is 20% to 50%.

[0028] According to one embodiment of the present invention, the doping concentration x is 30% to 50%.

[0029] According to one embodiment of the present invention, the doping concentration x is 40% to 50%.

[0030] According to one embodiment of the present invention, the doping concentration x further satisfies the following condition: after the doping concentration is increased to 1.2x-1.5x, the change in the conductivity of the hole injection layer is not greater than 20%.

[0031] According to one embodiment of the present invention, the doping concentration x further satisfies the following condition: after the doping concentration is increased to 1.2x-1.5x, the change in the conductivity of the hole injection layer is not greater than 10%.

[0032] According to one embodiment of the present invention, the thickness of the hole transport layer is greater than or equal to

[0033] According to one embodiment of the present invention, the thickness of the hole transport layer is greater than or equal to

[0034] According to one embodiment of the present invention, the thickness of the hole transport layer is less than or equal to

[0035] According to one embodiment of the present invention, the thickness of the hole transport layer is less than or equal to

[0036] According to one embodiment of the present invention, the electron blocking layer is the same as the hole injection layer.

[0037] In this embodiment, "same" means that the electron blocking layer and the hole injection layer are identical in terms of material, doping concentration, and thickness.

[0038] According to an embodiment of the present invention, a method for measuring the hole mobility of deep-level organic materials is disclosed, comprising the following steps:

[0039] a. Identify the first organic material;

[0040] b. Prepare a HOD device as described in any of the above embodiments;

[0041] c. Measure the JV data of the HOD device and calculate the hole mobility of the first organic material based on the data.

[0042] According to one embodiment of the present invention, it further includes: measuring the JV data of the HOD device and fitting J... 1 / 2 -V curve.

[0043] The HOD device disclosed in this invention realizes ohmic contact between the anode and the organic material, reduces the potential barrier between the organic layers, and further uses the HOD device to measure the hole mobility of deep-level organic materials, which can make the measurement results more accurate and reflect the true performance of the organic materials. Attached Figure Description

[0044] Figure 1 This is a cross-sectional schematic diagram of the HOD device of the present invention.

[0045] Figure 2 This is the experimental flowchart.

[0046] Figure 3 These are the JV characteristic curves corresponding to Examples 1-3 and Comparative Example 1.

[0047] Figure 4 These are the JV characteristic curves corresponding to Example 4 and Comparative Example 2.

[0048] Figure 5 These are the JV characteristic curves corresponding to Example 5 and Comparative Example 3.

[0049] Figure 6 It is a curve showing the change in conductivity with PD concentration. Detailed Implementation

[0050] This application provides a hole injection layer for a first organic material, formed by selecting a suitable first dopant based on the HOMO energy level of the first organic material and incorporating it into the first organic material. Alternatively, a second dopant can be incorporated into a second organic material to form the hole injection layer of the first organic material. The doping concentration of the dopant is optimized to ensure that the conductivity of the hole injection layer is greater than 10 × 10⁻⁶. -3 S / m. The hole mobility of the first organic material was further measured using the HOD device. Because the HOD device achieves ohmic contact between the anode and the organic material, it avoids or reduces the potential barrier between the hole injection layer and the first organic material, thus enabling a more accurate measurement of the hole mobility of the organic material.

[0051] As used herein, a "hole-only device (HOD)" refers to a device that allows holes from the anode to pass through, but not electrons from the cathode. An HOD device typically includes a substrate, an anode, a hole injection layer, a hole transport layer, an electron blocking layer, and a cathode. The hole injection layer facilitates hole injection from the anode into the organic layer under test, while the electron blocking layer blocks electron injection from the cathode into the hole transport layer. Generally, in an HOD device, the material used for the electron blocking layer can be the same as that used for the hole injection layer, or other suitable electron blocking layer materials can be used. Note that the cathode and anode used in the embodiments of this application are Ag and ITO, respectively, but other metals or metal oxides can also be used, such as Ag or IZO for the anode, and Yb, Mg, or Mg:Ag alloys for the cathode. HOD devices can also contain more layers; for example, an electron injection layer, such as Yb, LiF, or LiQ, can be inserted between the cathode and the electron blocking layer. Sometimes, a modifying layer, such as MoOx, can be added between the anode and the hole injection layer.

[0052] As used herein, "top" means furthest from the substrate, and "bottom" means closest to the substrate. When the first layer is described as being "disposed" on the second layer, the first layer is positioned further away from the substrate. Unless it is specified that the first layer "contacts" the second layer, other layers may exist between the first and second layers. For example, even if various organic layers exist between the cathode and anode, the cathode may still be described as being "disposed" on the anode.

[0053] The term "doping concentration" refers to the percentage of a single material in the total mass of an organic thin film.

[0054] As used herein, "encapsulation layer" can be a thin film encapsulation with a thickness of less than 100 micrometers, which includes one or more thin films directly deposited on the device, or it can be a cover glass adhered to a substrate.

[0055] In this paper, the HOMO (highest occupied orbital) and LUMO (lowest unoccupied orbital) energy levels were determined using electrochemical cyclic voltammetry, the most commonly used method for determining the energy levels of organic materials. The tests were conducted using a CorrTest CS120 electrochemical workstation manufactured by Wuhan CorrTest Instruments Co., Ltd., employing a three-electrode system: a platinum disk electrode as the working electrode, an Ag / AgNO3 electrode as the reference electrode, and a platinum wire electrode as the auxiliary electrode. Anhydrous DCM was used as the solvent, and 0.1 mol / L tetrabutylammonium hexafluorophosphate was used as the supporting electrolyte. The test compound was prepared by adding 10... -3For the mol / L solution, nitrogen gas was bubbled into the solution for 10 min to remove oxygen before the test. Instrument parameter settings: scan rate 100 mV / s, potential interval 0.5 mV, test window -1 V to 1 V.

[0056] In this paper, all "HOMO level" and "LUMO level" are represented by negative values. The smaller the value (i.e., the larger the absolute value), the deeper the energy level. The statement that an energy level is less than a certain number in this application means that the energy level is numerically smaller than that number, i.e., has a more negative value. For example, "the HOMO level of the first organic material is less than -5.0 eV" in this application means that the HOMO level of the first organic material is numerically more negative than -5.0 eV. In this paper, since the HOMO level of transport materials is usually deeper, the difference between the LUMO level of the doped material and the HOMO level of the first or second organic material being tested is generally a positive value.

[0057] In this article, "deep-level organic materials" refers to organic materials with a HOMO energy level of less than -5.0 eV.

[0058] The term "electrical conductivity" refers to the conductivity of a material under test in a high vacuum (e.g., 10⁻⁶ Ω·cm). -6 The electrode (approximately 100 nm thick, 6 mm long, and 1 mm wide) is deposited onto a test substrate pre-prepared with aluminum electrodes by vapor deposition, forming a test area with a thickness of 100 nm, a length of 6 mm, and a width of 1 mm. At room temperature, the resistance value of the area is obtained by measuring the current through applying a voltage to the electrode, and then the conductivity of the given thin film is calculated according to Ohm's law and the geometric dimensions.

[0059] It should be noted that the conductivity of the HIL layer in this embodiment was measured separately using the method described above.

[0060] The term "goodness of fit (R)" 2 "(Goodness of Fit)" refers to the degree to which the regression line fits the observed values. 2 The maximum value is 1. R 2 The closer the R value is to 1, the better the regression line fits the observed values; conversely, the closer the R value is to 1, the better the regression line fits the observed values. 2 The smaller the value, the worse the regression line fits the observed values.

[0061] The HOD device structure used in this application is anode / HIL / HTL / EBL / cathode. The material in the HTL layer is the organic material to be tested. The HIL has high conductivity, and the energy levels of the material used are very well matched with those of the material to be tested. Using the HOD device disclosed in this application to measure the hole mobility of organic materials allows for the measurement of the J-axis of the HOD device. 1 / 2 The -V curve is linear throughout the entire measurement area, avoiding errors introduced by judging inflection points and making the calculated hole mobility more accurate.

[0062] To achieve the above effects, it is essential to ensure a good ohmic contact between the HIL layer and the anode in the HOD device. This can be achieved by selecting a suitable dopant material (PD, p-type dopant) and a specific doping concentration. The HIL layer is typically formed by incorporating PD material into a hole transport host material (HTM). Generally, a good hole injection effect is achieved when the energy difference between the HOMO level of the HTM material and the LUMO level of the PD material is less than 0.20 eV. Beyond meeting the energy level difference requirement, the doping concentration of the PD material also needs to be adjusted to ensure ohmic contact. Generally, as the doping concentration of the PD material increases, the conductivity of the HIL layer initially increases and then remains relatively constant. Figure 6 The conductivity of the HIL layer was measured at different doping concentrations when the same PD material (PD-1) was incorporated into the same HTM material (HT-1). It can be seen that when the doping concentration of PD-1 is less than 40%, the conductivity of the HIL layer increases significantly with increasing doping concentration; however, when the doping concentration of PD-1 is between 40% and 60%, the conductivity of the HIL layer remains essentially unchanged. This indicates that the doping concentration of PD material (PD-1) in HTM material (HT-1) essentially peaks around 40%. When the doping concentration of PD material is further increased to 60%, the change in hole injection layer conductivity is no greater than 30%, indicating that the doping of PD material in the HTM material has reached saturation. At this point, the HIL layer and the anode can form a good ohmic contact.

[0063] While achieving good ohmic contact, it is also important to consider the energy level difference between different film layers in the HOD device (in this application, the energy level of the HIL layer refers to the energy level of the first or second organic material of the HIL layer), i.e., the potential barrier. If a high potential barrier exists from the HIL layer to the HTL layer, it will increase the overall voltage of the HOD device, i.e., increase the additional resistance, affecting the accuracy of the mobility measurement of the first organic material. Therefore, the HTM material of the HIL layer is preferably a material with the same energy level as the first organic material, or the first organic material can be used directly as the HTM material. This is challenging for first organic materials with deep HOMO levels (e.g., less than -5.0 eV): it may be difficult to find a suitable PD material to match. In this case, a second organic material and another PD material (with a LUMO level of LUMO2) can be selected. The HOMO level HOMO2 of the second organic material needs to satisfy 0 ≤ HOMO2 - HOMO1 ≤ 0.22 eV, and simultaneously satisfy LUMO2 - HOMO2 < 0.20 eV. When a second organic material is used in the HIL layer, although there is a potential barrier from the HIL layer to the first organic material, this barrier is very small and its impact is very limited. The calculated hole mobility will be closer to the true value.

[0064] The above methods can be summarized as follows: Figure 2 The experimental flowchart is shown.

[0065] Step 1: Identify the first organic material with a HOMO energy level less than -5.0 eV;

[0066] Step 2: Fabricate the HOD device, which includes a cathode, an anode, and a hole injection layer, a hole transport layer, and an electron blocking layer disposed between the cathode and the anode;

[0067] The hole injection layer is formed by doping a first doped material (LUMO level LUMO1) with a mass ratio doping concentration x in a first organic material (HOMO level HOMO1), or by doping a second doped material (LUMO level LUMO2) with a mass ratio doping concentration x in a second organic material (HOMO level HOMO2).

[0068] HOMO1, HOMO2, LUMO1, and LUMO2 satisfy the following conditions:

[0069] HOMO1<-5.0eV; 0≤HOMO2-HOMO1≤0.22eV; LUMO1-HOMO1≤0.20eV; LUMO2–HOMO2≤0.20eV;

[0070] The doping concentration x can be any value that simultaneously satisfies the following conditions:

[0071] i. The doping concentration x is 1% to 60%;

[0072] ii. Make the electrical conductivity of the hole injection layer greater than 10 × 10⁻⁶. -3 S / m;

[0073] iii. After the doping concentration is increased to 1.2x to 1.5x, the change in conductivity of the hole injection layer is no more than 30%;

[0074] A first organic material is vapor-deposited onto the hole injection layer to form the hole transport layer; the electron blocking layer is vapor-deposited onto the hole transport layer.

[0075] Step 3: Measure the JV data of the HOD device and fit the JV data of the HOD device. 1 / 2 -V curves were obtained, and the hole mobility of the first organic material was calculated according to the Mott-Gurney equation.

[0076] The Mott-Gurney equation is as follows:

[0077]

[0078] In the equation, ε r It is the relative permittivity of organic materials, ε o d is the vacuum dielectric constant, d is the sample thickness, and J is the current density (unit: A / m). 2 V is voltage, measured in volts (V); μ is the carrier mobility of the material under test; ε is the relative permittivity of the organic material. r =3, vacuum permittivity is ε o =8.85×10 -12 F / m, the thickness of the first organic material to be tested is 100 nm, J 1 / 2 / V is J 1 / 2 - The slope of the V curve.

[0079] The present invention will be described in more detail below with reference to the following embodiments. It is obvious that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Based on the following embodiments, those skilled in the art can obtain other embodiments of the invention through modifications.

[0080] Example 1: Preparation of such Figure 1 The HOD1 device 100 shown is illustrated.

[0081] The first organic material HT-1 is selected, with a HOMO level of -5.27 eV. The first doped material PD-1 is selected, with a LUMO level of -5.17 eV, satisfying the LUMO requirement. PD-1 -HOMO HT-1 =0.10eV≤0.20eV, doping material PD-1 is incorporated into organic material HT-1. The conductivity of the film at different doping concentrations is measured using the method provided by this invention. The conductivity of the film at a doping concentration of 40% for doping material PD-1 is 28.5×10⁻⁶. -3 S / m, greater than 10×10 -3 The conductivity is S / m, and when the doping concentration of the doped material PD-1 is 50%, the conductivity is 29.5 × 10⁻⁶. -3 With a conductivity change rate of 3.5% (S / m), which is less than 30%, the doping concentration x is determined to be 40%.

[0082] The HOD1 device was fabricated using the aforementioned organic materials: First, a 0.7 mm thick glass substrate with a pre-patterned design was used. A thick indium tin oxide (ITO) substrate was used as the anode 110. After washing the substrate with deionized water and detergent, the ITO surface was treated with oxygen plasma and UV ozone. Subsequently, the substrate was dried in a glove box to remove moisture and then placed on a support and transferred to a vacuum chamber. The organic layer specified below was applied at a vacuum degree of approximately 10... -6 In the case of Torr, The rate was achieved by sequentially depositing compounds HT-1 and PD-1 onto the anode layer via vacuum thermal evaporation: first, compounds HT-1 and PD-1 were simultaneously deposited as hole injection layers (HIL, 60:40). )120, vapor-deposited compound HT-1 as hole transport layer (HTL, )130, while simultaneously depositing compounds HT-1 and PD-1 as electron blocking layers (HIL, 60:40, )140, Finally, metallic silver is vapor-deposited as the cathode (Cathode, 150. The device is then transferred back to the glove box and sealed with a glass cover (160) to complete the device.

[0083] Example 2: Fabrication of HOD2 Device

[0084] As shown in Example 1, when the doping concentration of the doped material PD-1 is 50%, the conductivity is 29.5 × 10⁻⁶. -3 S / m was further measured, and the conductivity of PD-1 at a doping concentration of 60% was 30.0 × 10⁻⁶. -3 With a conductivity change rate of 1.7% (S / m), which is less than 30%, the doping concentration x of 50% also meets the condition.

[0085] Fabrication of HOD2 devices: The fabrication method is the same as in Example 1, except that the doping concentration of compound PD-1 in both the HIL layer and EBL layer is increased to 50%.

[0086] Example 3: Fabrication of HOD3 Device

[0087] The second organic material chosen is HT-2, whose HOMO level is -5.13 eV, satisfying 0 ≤ HOMO. HT-2 -HOMO HT-1 =0.14eV < 0.22eV, so the second doped material PD-2 is selected, whose LUMO level is -5.04eV, satisfying the LUMO requirement. PD-2 -HOMO HT-2 =0.09eV < 0.2eV. Doping material PD-2 was incorporated into organic material HT-2. The conductivity of the film at different doping concentrations was measured using the method provided by this invention. When PD-2 was incorporated into HT-2 at a doping concentration of 40%, the measured conductivity was 16.6 × 10⁻⁶. -3 S / m, greater than 10×10 -3 When PD-2 is incorporated into HT-2 at a doping concentration of 50%, the measured conductivity is 15.1 × 10⁻⁶ S / m. -3 With a conductivity change rate of 9.0% (S / m), which is less than 30%, the doping concentration x is determined to be 40%.

[0088] Fabrication of HOD3 devices: The fabrication method is the same as in Example 1, except that HIL and EBL are replaced with: simultaneous evaporation of compound HT-2 and compound PD-2 (60:40). As the hole injection layer 120, compound HT-2 and compound PD-2 (60:40) were simultaneously deposited. ) as an electron blocking layer 140.

[0089] Example 4: Fabrication of HOD4 Device

[0090] The first organic material HT-3 was selected, with a HOMO level of -5.33 eV. The first doped material PD-1, with a LUMO level of -5.17 eV, was selected to satisfy the LUMO requirement. PD-1 -HOMO HT-3 =0.16eV < 0.2eV. The conductivity of the film at different doping concentrations was measured by incorporating doping material PD-1 into the organic material HT-3 using the method provided by this invention. When PD-1 was incorporated into HT-3 at a doping concentration of 40%, the measured conductivity was 54.7 × 10⁻⁶ eV. -3 S / m, greater than 10×10 -3 When PD-1 is incorporated into HT-3 at a doping concentration of 50%, the measured conductivity is 51.4 × 10⁻⁶ S / m. -3 With a conductivity change rate of 6.0% (S / m), which is less than 30%, the doping concentration x is determined to be 40%.

[0091] Fabrication of HOD4 devices: The fabrication method was the same as in Example 1, except that HIL, HTL, and EBL were replaced with: simultaneous evaporation of compound HT-3 and compound PD-1 (60:40). ) as the hole injection layer 120, and HT-3, a vapor-deposited compound, as the hole transport layer (HTL). )130, and simultaneously vapor-deposited compounds HT-3 and PD-1 (60:40, ) as an electron blocking layer 140.

[0092] Example 5: Fabrication of HOD5 ​​Device

[0093] The first organic material HT-4 was selected, and its HOMO level was measured to be -5.35 eV. Then, the first dopant PD-1, with a LUMO level of -5.17 eV, was incorporated, satisfying the LUMO requirement. PD-1 -HOMO HT-4=0.18eV < 0.2eV. The conductivity of the film at different doping concentrations was measured by incorporating doping material PD-1 into the organic material HT-4 using the method provided by this invention. When PD-1 was incorporated into HT-4 at a doping concentration of 40%, the measured conductivity was 13.1 × 10⁻⁶. -3 S / m, greater than 10×10 -3 When PD-1 is incorporated into HT-4 at a doping concentration of 50%, the measured conductivity is 13.4 × 10⁻⁶ S / m. -3 With a conductivity change rate of 2.3% (S / m), which is less than 30%, the doping concentration x is determined to be 40%.

[0094] Fabrication of HOD5 ​​devices: The fabrication method is the same as in Example 1, except that HIL, HTL, and EBL are replaced with: simultaneous evaporation of compound HT-4 and compound PD-1 (60:40). ) as the hole injection layer 120, and HT-4, a vapor-deposited compound, as the hole transport layer (HTL). )130, and simultaneously vapor-deposited compounds HT-4 and PD-1 (60:40, ) as an electron blocking layer 140.

[0095] Comparative Example 1: Fabrication of HOD6 Devices

[0096] The difference from Example 1 is that the doped material PD-1 is incorporated into HT-1 at a doping concentration of 3%, and the measured conductivity is 0.37 × 10⁻⁶. -3 S / m, less than 10×10 -3 S / m does not meet the limitation on doping concentration x in this invention.

[0097] Fabrication of HOD6 devices: The fabrication method is the same as in Example 1, except that the doping concentration of compound PD-1 in both the HIL layer and EBL layer is reduced to 3%.

[0098] Comparative Example 2: Fabrication of HOD7 Device

[0099] Compound HT-5 was selected, with a HOMO level of -5.09 eV. The energy difference between HT-5 and the test compound HT-3 (HOMO level -5.33 eV) is HOMO 5.09 eV. HT-5 -HOMO HT-3 =0.24eV > 0.22eV, which does not meet the requirements for the second organic material in this invention. Therefore, PD-2, a dopant material paired with compound HT-5, was selected. The LUMO level of PD-2 is -5.04eV, which satisfies the LUMO requirement. PD-2 -HOMO HT-5 =0.05eV < 0.2eV.

[0100] Fabrication of HOD7 devices: The fabrication method is the same as in Example 4, except that HIL and EBL are replaced with: simultaneous evaporation of compound HT-5 and compound PD-2 (60:40). ) as hole injection layer 120 and simultaneously deposited compound HT-5 and compound PD-2 (60:40, ) as an electron blocking layer 140.

[0101] Comparative Example 3: Fabrication of HOD8 Devices

[0102] The first organic material HT-4 has a HOMO level of -5.34 eV, while the first doped material PD-2, which incorporates a LUMO level of -5.03 eV, has a LUMO level of -5.03 eV. PD-2 -HOMO HT-4 =0.31eV > 0.2eV, which does not meet the energy level difference requirement between the first organic material and the first doped material in this invention. Furthermore, when PD-2 is incorporated into HT-4 at a doping concentration of 40%, the measured conductivity is only 0.05 × 10⁻⁶. -3 S / m, less than 10×10 -3 S / m also does not meet the limitation on doping concentration x in this invention.

[0103] Fabrication of HOD8 devices: The fabrication method in Example 5 is the same, except that HIL and EBL are replaced with: simultaneous evaporation of compound HT-4 and compound PD-2 (60:40). As the hole injection layer 120, compound HT-4 and compound PD-2 (60:40) were simultaneously deposited. ) as an electron blocking layer 140.

[0104] Table 1 lists the organic layer structures of the HOD1-HOD8 devices. The layers are made of more than one material and are obtained by doping different compounds in the weight ratios specified therein.

[0105] Table 1 Organic layer structure of HOD1-HOD8 devices

[0106]

[0107]

[0108] The structure of the compound used in the device is shown below:

[0109]

[0110] Hole mobility of the organic material under test was measured using the HOD1-HOD8 device in the above embodiments and comparative examples: JV data of the HOD1-HOD8 device were measured, and J was fitted based on the measured JV data.1 / 2 -V curve, J 1 / 2 The slope of the -V curve was substituted into the Mott-Gurney equation to calculate the hole mobility of the organic material. A total of 8 sets of data were measured, and the J value was obtained through fitting. 1 / 2 -V curve, see Figures 3-5 .

[0111] from Figure 3 It can be seen that the J corresponding to the HOD1-HOD3 devices in Examples 1-3 1 / 2 -V shows a linear relationship, and the goodness of fit R0 2 Both are 1, which conforms to the SCLC model, meaning that the hole mobility of HT-1 can be calculated using the Mott-Gurney equation. Figure 3 J of HOD1 and HOD2 devices 1 / 2 The -V relationships are y = 23.143x + 2.1816 and y = 23.049x + 2.1938, respectively. The relative permittivity of the organic material is 3, and the vacuum permittivity is 8.85 × 10⁻⁶. -12 F / m, the thickness of the organic material to be tested (the thickness of the HTL layer) is 100 nm. According to the equation, the hole mobility of HT-1 under the two device structures is 18.0 × 10⁻⁶. -5 cm 2 / (Vs) and 17.9×10 -5 cm 2 / (Vs); J of HOD3 device 1 / 2 The -V curve is y = 7.078222.383x - 0.2249, and the hole mobility of HT-1 is calculated to be 16.8 × 10⁻⁶. -5 cm 2 / (Vs).

[0112] J of the HOD6 device in Comparative Example 1 1 / 2 The -V curve is not a nonlinear curve; it exhibits an ohmic conductivity region and a SCLC conductivity region. In this case, it is difficult to accurately pinpoint the starting point of the SCLC conductivity region. If we take the voltage at 2V as the starting point, the fitted curve is y = 17.085x - 27.292, R... 2 =0.9982, and the hole mobility of HT-1 is calculated to be 9.8 × 10⁻⁶ according to the Mott-Gurney equation. -5 cm 2 / (Vs).

[0113] from Figure 4 It can be seen that the J of the HOD4 device in Example 4 1 / 2 The -V curve is y = 56.309x + 7.9404, and the goodness of fit RV is 7.9404. 2=0.9959, which conforms to the SCLC model. The hole mobility of HT-3 calculated using the Mott-Gurney equation is 106.5 × 10⁻⁶. - 5 cm 2 / (Vs); J of the HOD7 device in Comparative Example 2 1 / 2 The -V curve is y = 28.318x - 2.2376, R 2 =0.9991, and the hole mobility of HT-3 calculated according to the Mott-Gurney equation is 26.9 × 10⁻⁶. -5 cm 2 / (Vs).

[0114] from Figure 5 It can be seen that the J of the HOD5 ​​device in Example 5 1 / 2 The -V curve is y = 13.229x - 12.975, and the goodness of fit RV is 12.975. 2 =0.9977, which conforms to the SCLC model. The hole mobility of HT-4 is calculated to be 5.9 × 10⁻⁶ using the Mott-Gurney equation. -5 cm 2 / (Vs); J of the HOD8 device in Comparative Example 3 1 / 2 The -V curve is y = 8.4156x - 5.7083, R 2 =0.9983, and the hole mobility of HT-4 is calculated to be 2.4 × 10⁻⁶ according to the Mott-Gurney equation. -5 cm 2 / (Vs).

[0115] In Examples 1-3, the doping concentration of the doped material in the hole injection layer of the HOD1-HOD3 devices reached its peak, resulting in high conductivity. This ensured a good ohmic contact between the hole injection layer and the anode, guaranteeing carrier injection. Furthermore, the use of the same or similarly energy-level organic materials in the hole injection layer and hole transport layer reduced the contact barrier between the layers, avoiding contact resistance. Therefore, the J-value fitted using the HOD1-HOD3 devices... 1 / 2 The -V curve conforms to the SCLC model, and the measured hole mobility of HT-1 is more accurate. However, the HOD6 device in Comparative Example 1, due to insufficient conductivity of its HIL layer, lacks an ohmic contact, and there is a potential barrier between different film layers, all of which introduce additional resistance. Even under high current injection conditions, the influence of this resistance, while reduced, does not completely disappear. Therefore, the J obtained using this device... 1 / 2The -V curve is not perfectly linear, so it is necessary to select an inflection point (i.e., after this inflection point, it conforms to the SCLC model) to calculate the hole mobility. In this application, 2V is selected as the inflection point, and the measured hole mobility of HT-1 is 9.8 × 10⁻⁶. -5 cm 2 / (Vs), this value is approximately 18.0 × 10⁻⁶ measured by the HOD1-HOD2 devices. -5 cm 2 The difference between / (Vs) and Vs is significant, which clearly cannot accurately reflect the hole mobility of the material. Moreover, the choice of the inflection point is highly subjective; choosing an inflection point less than or greater than 2V will lead to different measurement results. Therefore, the HOD6 device in Comparative Example 1 cannot provide an accurate hole mobility value.

[0116] In Example 4, the HOD4 device exhibits high conductivity in its hole injection layer, forming a good ohmic contact between the anode and the hole injection layer. Furthermore, the hole injection layer utilizes the same first organic material as the hole transport layer, reducing the potential barrier difference between layers. Using this device, the hole mobility of HT-3 was measured to be 106.5 × 10⁻⁶. -5 cm 2 / (Vs); In Comparative Example 2, although the hole injection layer of the HOD7 device also has a relatively high conductivity, the energy level difference between its hole injection layer and hole transport layer is large, resulting in an increased potential barrier between the film layers. Consequently, the measured hole mobility of HT-3 is low, only 26.9 × 10⁻⁶. -5 cm 2 / (Vs), compared to Example 4, shows a 75% lower hole mobility, which clearly does not accurately reflect the hole mobility of the material. This demonstrates that simply ensuring hole injection without considering the energy level differences between film layers can lead to significant measurement errors.

[0117] In Example 5, the hole injection layer of the HOD5 ​​device used doped material PD-1 and the tested organic material HT-4. The energy level difference between the two materials is small, and the conductivity meets the requirements. The measured hole mobility of HT-4 is 5.9 × 10⁻⁶. -5 cm 2 / (Vs); In Comparative Example 3's HOD8 device, another doping material, PD-2, was selected. The energy level difference between PD-2 and the test material HT-4 is large. Even when the doping concentration of PD-2 reaches 40%, the conductivity remains low. This may be because the large energy level difference between PD-2 and HT-4 prevents effective doping, limiting carrier injection and thus affecting the formation of the space charge region. Therefore, the hole mobility of HT-4 measured by the HOD8 device in Comparative Example 3 is low, only 2.4 × 10⁻⁶. -5 cm 2 / (Vs), which is 59% lower than the hole mobility measured by the HOD5 ​​device in Example 5.

[0118] In summary, we disclose a hole-transporting device (HOD) in which a first organic material is used to form a hole transport layer, and a suitable p-type dopant is incorporated into either the first or second organic material to form a hole injection layer. Optimizing the doping concentration of the p-type dopant causes the conductivity of the hole injection layer to approach its peak value. Furthermore, using this HOD device to measure the hole mobility of the first organic material, the unique design of the device achieves ohmic contact between the anode and the organic material, and avoids or reduces the potential barrier between the hole injection layer and the first organic material, enabling a more accurate measurement of the hole mobility of the organic material and reflecting its true performance.

[0119] It should be understood that the various embodiments described herein are merely examples and are not intended to limit the scope of the invention. Therefore, as will be apparent to those skilled in the art, the claimed invention may include variations of the specific embodiments and preferred embodiments described herein. Many of the materials and structures described herein can be substituted with other materials and structures without departing from the spirit of the invention. It should be understood that various theories regarding why the invention works are not intended to be limiting.

Claims

1. A HOD device comprising an anode, a cathode, and a hole injection layer, a hole transport layer, and an electron blocking layer disposed between the anode and the cathode; The hole transport layer is formed of a first organic material; The hole injection layer is formed by doping a first doping material in a first organic material at a mass ratio of doping concentration x, or by doping a second doping material in a second organic material at a mass ratio of doping concentration x. The HOMO level of the first organic material is HOMO1, the HOMO level of the second organic material is HOMO2, the LUMO level of the first doped material is LUMO1, and the LUMO level of the second doped material is LUMO2. HOMO1, HOMO2, LUMO1, and LUMO2 satisfy the following conditions: HOMO1<-5.0 eV; 0 ≤ HOMO2- HOMO1≤ 0.22 eV; LUMO1- HOMO1≤ 0.20 eV; LUMO2- HOMO2≤ 0.20 eV; The doping concentration x can be any value that simultaneously satisfies the following conditions: i. The doping concentration x is 1% to 60%; ii. Make the electrical conductivity of the hole injection layer greater than 10 × 10⁻⁶. -3 S / m; iii. After the doping concentration is increased to 1.2x~1.5x, the change in conductivity of the hole injection layer is no more than 30%.

2. The HOD device as described in claim 1, wherein, HOMO1 ≤ -5.2 eV.

3. The HOD device as described in claim 1, wherein, HOMO1 ≤ -5.3 eV.

4. The HOD device as described in claim 1, wherein, LUMO1- HOMO1≤ 0.15 eV.

5. The HOD device as described in claim 1, wherein, 0 ≤ HOMO2- HOMO1 ≤ 0.20 eV.

6. The HOD device as claimed in claim 1, wherein, A good ohmic contact can be formed between the anode and the hole injection layer.

7. The HOD device as claimed in claim 1, wherein, The doping concentration x is 5% to 50%.

8. The HOD device as claimed in claim 1, wherein, The doping concentration x is 10% to 50%.

9. The HOD device as claimed in claim 1, wherein, The doping concentration x is 40% to 50%.

10. The HOD device as claimed in claim 1, wherein, The doping concentration x also satisfies the following condition: after the doping concentration is increased to 1.2x-1.5x, the change in conductivity of the hole injection layer is no greater than 20%.

11. The HOD device as claimed in claim 1, wherein, The thickness of the hole transport layer is greater than or equal to 400 Å.

12. The HOD device as claimed in claim 1, wherein, The thickness of the hole transport layer is greater than or equal to 1000 Å.

13. The HOD device as claimed in claim 1, wherein, The electron blocking layer is the same as the hole injection layer.

14. A method for measuring hole mobility in deep-level organic materials, comprising the following steps: a. Identify the first organic material; b. To prepare a HOD device as described in any one of claims 1-13; c. Measure the JV data of the HOD device and calculate the hole mobility of the first organic material based on the data.

15. The method of claim 14, further comprising: Measure the JV data of the HOD device and fit the J... 1 / 2 -V curve.

Images