Low-work-function transparent conductive cathode and preparation method thereof

Abstract

The invention discloses a low work function transparent conductive cathode and a preparation method thereof, the low work function transparent conductive cathode comprises a transparent substrate, an ultra-thin metal aluminum layer and an indium oxide layer which are stacked, the ultra-thin metal aluminum layer is located above the transparent substrate, the thickness of the ultra-thin metal aluminum layer is 0.5 nm-2 nm, the indium oxide layer is located above the ultra-thin metal aluminum layer, and the thickness of the indium oxide layer is 0.5 nm-2 nm. And the indium oxide layer is a zirconium and gallium doped indium oxide film with the thickness of 200nm-500nm. The invention aims to provide a low-work-function transparent conductive cathode and a preparation method thereof. The cathode structure can effectively reduce the interface contact potential barrier and realize efficient electron injection, and the preparation process is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the technical field of conductive cathodes, specifically to a low work function transparent conductive cathode and its preparation method. Background Technology

[0002] Transparent conductive electrodes combine excellent visible light transmittance with good conductivity, making them an indispensable basic material in the modern optoelectronics and electronics industry. They are widely used in flat panel displays, touch screens, sensors, and various photovoltaic cells.

[0003] Currently, the most commercially viable transparent conductive materials are primarily n-type semiconductor metal oxide (TCO) thin films, such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO). However, these traditional TCO materials typically possess high work functions (usually >4.7 eV), making them ideal as anodes for hole collection or injection. With the rapid development of optoelectronic technology, novel device structures such as semi-transparent perovskite solar cells (ST-PSCs) and inverted organic light-emitting diodes (OLEDs) are constantly emerging. In these devices, to achieve specific optical path designs (such as light entering or exiting from the cathode side), there is an urgent need for a cathode material that is both transparent and capable of efficiently collecting or injecting electrons. This requires the cathode material to not only possess excellent optoelectronic properties but also have a low work function to match the energy levels of the active layer.

[0004] However, existing low work function cathode materials typically employ reactive metals such as calcium (Ca), magnesium (Mg), aluminum (Al), or silver (Ag). These metals not only have poor optical transparency but are also chemically reactive, making them highly susceptible to oxidation and failure in air, resulting in insufficient device stability. Conversely, if traditional high work function TCO films such as ITO are directly forced as cathodes, severe interfacial energy level mismatch will lead to the formation of Schottky contacts rather than ideal ohmic contacts at the electrode / active layer interface. The resulting large contact barrier severely hinders the efficient transport and extraction of electron carriers, significantly reducing device performance.

[0005] To address the aforementioned contradiction between transparency, conductivity, and low work function, existing technologies have explored various approaches. For instance, patent document CN112908517A discloses a multilayer composite transparent conductive film of "conductive oxide / metal or carbon material / conductive oxide." While this structure achieves a balance between transmittance (85%-90%) and sheet resistance (0.1Ω / sq - 9Ω / sq) to some extent, its fabrication process is complex and costly, and this technical solution does not explicitly propose an effective method to reduce the surface work function.

[0006] Another patent document, CN101436636A, proposes a transparent conductive cathode contact structure for n-type silicon solar cells, which improves the interface by first depositing an ultrathin lithium fluoride (LiF) insulating layer on the n-type silicon surface. However, this method has obvious limitations. Its interface modification mechanism is only effective for specific crystalline silicon materials and cannot be universally extended to other types of novel thin-film optoelectronic devices. Furthermore, the deposition process of LiF thin films is relatively complex, making it difficult to meet the needs of large-area, low-cost industrial production.

[0007] Therefore, developing a transparent conductive cathode material that combines high transmittance, high conductivity, low work function, simple fabrication process, good environmental stability, and strong versatility is a key technical problem that urgently needs to be solved in the field of optoelectronic devices. Summary of the Invention

[0008] To address the problem that existing transparent conductive materials often fail to simultaneously achieve low work function, high transmittance, and low resistivity for cathode applications, this invention aims to provide a low work function transparent conductive cathode and its fabrication method. This cathode structure effectively reduces the interfacial contact barrier, enabling efficient electron injection, and its fabrication process is suitable for industrial production.

[0009] To achieve the above objectives, the present invention employs a low work function transparent conductive cathode, comprising a transparent substrate, an extremely thin aluminum layer, and an indium oxide layer stacked together. The extremely thin aluminum layer is located above the transparent substrate and has a thickness of 0.5 nm to 2 nm. The indium oxide layer is located above the extremely thin aluminum layer and is an indium oxide thin film with a thickness of 200 nm to 500 nm and doped with zirconium and gallium.

[0010] As a further optimization of the above scheme, the material of the transparent substrate is selected from glass, polyethylene terephthalate, polyethylene naphthalate, or polyimide.

[0011] As a further optimization of the above scheme, in the indium oxide thin film doped with zirconium and gallium, the doping atomic ratio of zirconium is 1%-3% and the doping atomic ratio of gallium is 1%-5%.

[0012] As a further optimization of the above scheme, the work function of the transparent conductive cathode is less than 4.2 eV.

[0013] A method for preparing a low work function transparent conductive cathode includes the following steps: Step S1: Provide a transparent substrate and heat the transparent substrate to a preset temperature; Step S2: An extremely thin layer of metallic aluminum is formed by cyclic deposition on the transparent substrate using atomic layer deposition. Step S3: A high-power pulsed magnetron sputtering and DC sputtering co-sputtering method is used to deposit and form an indium oxide thin film doped with zirconium and gallium on the ultra-thin aluminum layer; Step S4: Vacuum annealing is performed on the deposited indium oxide thin film to obtain a low work function transparent conductive cathode. As a further optimization of the above scheme, in step S1, the set temperature of the transparent substrate 1 is 120°C. In step S2, triethylaluminum is used as an aluminum source precursor, and the pulse duration of the aluminum source precursor is 1s to 4s. A mixture of nitrogen and hydrogen is used as a reducing agent, and the pulse duration of the reducing agent is 15 seconds. Nitrogen gas was introduced for purging, and the purging time was 10 seconds. The atomic layer deposition process involves 3 to 10 cycles.

[0014] As a further optimization of the above scheme, the volume ratio of the nitrogen to hydrogen mixture is 96:4.

[0015] As a further optimization of the above scheme, in step S3, a gallium-doped indium oxide target is connected to a high-power pulsed magnetron sputtering power supply, and a zirconium metal target is connected to a DC power supply for co-sputtering. During the sputtering process, a DC negative bias voltage is applied to the substrate, and the mass ratio of gallium oxide to indium oxide in the gallium-doped indium oxide target is 5%.

[0016] As a further optimization of the above scheme, the high-power pulsed magnetron sputtering power supply has a pulse power of 150W to 300W, a pulse width of 150μs, and a pulse frequency of 100Hz. The DC power supply has a sputtering power of 30W to 60W, a working gas pressure of 0.3Pa to 0.7Pa, an argon flow rate of 20sccm, a DC negative bias voltage applied to the substrate of -75V, and a total sputtering time of 13 minutes to 31 minutes.

[0017] As a further optimization of the above scheme, the process parameters for vacuum annealing in step S4 are: vacuum degree of 1 Pa, annealing temperature of 200℃ to 400℃, and annealing time of 45 minutes to 70 minutes.

[0018] The present invention provides a low work function transparent conductive cathode and its preparation method, which has the following beneficial effects: 1. The low work function transparent conductive cathode prepared by this invention simultaneously achieves excellent comprehensive performance of high transmittance, high conductivity, and low work function (<4.2 eV). When used as a device cathode, it can form a good ohmic contact with the active layer instead of an unfavorable Schottky contact, significantly reducing the interface barrier and improving device efficiency.

[0019] 2. The preparation method provided by this invention has a simple and clear process flow. The core steps (sputtering and annealing) are easy to upgrade and integrate on existing industrial-grade vacuum coating equipment, which has good feasibility for mass production and can effectively reduce production costs.

[0020] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and the embodiments of the present invention include many changes, modifications and equivalents. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a low work function transparent conductive cathode prepared according to the present invention; Figure 2 This is a flowchart illustrating the fabrication process of a low work function transparent conductive cathode and its preparation method. Figure 3 This is a UPS test diagram of the actual sample prepared in Example 1 of the present invention; Figure 4 This is a transmittance test chart of the actual sample prepared in Example 1 of the present invention.

[0022] Figure 5 This is a UPS test diagram of the actual sample prepared in the comparative example of this invention.

[0023] In the figure: 1. Transparent substrate; 2. Extremely thin aluminum layer; 3. Indium oxide layer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0025] It should be noted that when an element is referred to as "set on" or "provided with" another element, it can be directly on the other element or there may be an intermediate element. When an element is referred to as "connected to" or "connected to" another element, it can be directly connected to the other element or there may be an intermediate element at the same time. "Fixed connection" means fixed connection. There are many ways of fixed connection, which are not within the scope of protection of this document. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this document are only for illustrative purposes and do not represent the only implementation method.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in the specification herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. This invention provides a low work function transparent conductive cathode, the structure of which is as follows: Figure 1 As shown, from bottom to top, it includes a transparent substrate 1, an ultrathin aluminum layer 2, and an indium oxide layer 3. The ultrathin aluminum layer 2 is a dense elemental aluminum film with a thickness ranging from 0.5 to 2 nm; the indium oxide layer 3 is an indium oxide (In2O3) film doped with zirconium (Zr) and gallium (Ga) with a thickness ranging from 200 to 500 nm.

[0027] This invention, through experimental research, reveals that the doping ratio of Zr and Ga elements in the In2O3 thin film can be effectively altered by controlling the preparation process parameters described later. When the atomic ratio of Zr doping is controlled within the range of 1% to 3% and the atomic ratio of Ga doping is controlled within the range of 1% to 5%, combined with the underlying ultra-thin aluminum metal layer structure, the work function of the obtained composite conductive cathode can be stably lower than 4.2 eV.

[0028] It should be noted that, in this invention, there are no particular limitations on the material of the transparent substrate 1, as long as it can meet the light transmittance requirements of the device and withstand the temperature of subsequent fabrication processes. Preferably, the transparent substrate can be selected from any one of glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI).

[0029] The following specific embodiments illustrate the preparation method of the low work function transparent conductive cathode of the present invention.

[0030] Example 1: This embodiment provides a method for preparing a low work function transparent conductive cathode, such as... Figure 2 The flowchart shown includes the following steps: S1, Preparation of an ultrathin aluminum layer: A clean, transparent glass substrate was selected and placed in the reaction chamber of an atomic layer deposition (ALD) apparatus, and the substrate was heated to 120°C. Triethylaluminum (TMA) was used as the aluminum source precursor, with a pulse duration of 1 s when introduced into the reaction chamber; a N2 / H2 mixture with a volume ratio of 96:4 was used as the reducing agent, with a pulse duration of 15 s when introduced into the reaction chamber; after each introduction of reactants, high-purity N2 was used for purging, with a purging time of 10 s. The cycle number was set to 3 times. Finally, a dense, ultrathin aluminum layer with a thickness of approximately 0.5 nm was obtained on the surface of the glass substrate. The introduction of this ultrathin aluminum layer helps to improve the overall transmittance of the conductive cathode while reducing its resistivity.

[0031] It should be noted that, in some embodiments, the above-described atomic layer deposition method can be performed in a cyclic deposition sequence of "TMA pulse - N2 purging - N2 / H2 reducing agent pulse - N2 purging".

[0032] S2, Preparation of Zr and Ga-doped In2O3 thin films: The substrate with an extremely thin aluminum layer deposited in step S1 is transferred to the vacuum chamber of a magnetron sputtering apparatus, and the base vacuum is evacuated to ≤ 5 × 10⁻⁶. -4 After Pa, high-purity argon gas was introduced as the working gas, with the argon flow rate adjusted to 20 sccm and the working pressure stabilized at 0.7 Pa. A Ga-doped In₂O₃ target was used as the first target, with a Ga₂O₃ to In₂O₃ mass ratio of 5%, connected to a high-power pulsed magnetron sputtering power supply. A Zr target was used as the second target, connected to a DC power supply. The DC negative bias power supply connected to the substrate was turned on and set to -75V. The pulse power of the high-power pulsed magnetron sputtering power supply was set to 300W, the pulse width to 150μs, and the pulse frequency to 100Hz. The sputtering time for the Ga-doped In₂O₃ target was set to 10 min. Simultaneously, the sputtering power of the DC power supply was set to 30W, and the sputtering time for the Zr target was set to 6 min. A Zr- and Ga-doped In₂O₃ film with a thickness of approximately 200 nm was deposited on the surface of an extremely thin aluminum layer through dual-target co-sputtering.

[0033] In some embodiments, before turning on the DC negative bias power supply connected to the substrate, a high-power pulsed magnetron sputtering power supply and a DC power supply can be turned on simultaneously for pre-sputtering for 5 minutes to clean the target surface.

[0034] S3, Vacuum Annealing: After sputtering is complete and the sample has naturally cooled to room temperature in the vacuum chamber, the sample is removed and transferred to a vacuum annealing furnace. The annealing furnace is evacuated to 1 Pa, then heated to 400℃ and held for annealing for 45 min. After annealing, the sample is naturally cooled to room temperature to obtain a low work function transparent conductive cathode.

[0035] Performance testing: combined Figure 3 and Figure 4 The test results shown characterize the performance of the low work function transparent conductive cathode prepared in this embodiment. Ultraviolet photoelectron spectroscopy (UPS) testing indicates a work function of 4.19 eV. Transmittance and sheet resistance tests show that the cathode has an average transmittance of 86.9% and a sheet resistance of 11.2 Ω / □ in the wavelength range of 400–1000 nm.

[0036] Example 2: This embodiment provides another method for preparing a low work function transparent conductive cathode, which specifically includes the following steps: S1. Using PEN as the substrate, an aluminum layer was prepared on the substrate using atomic layer deposition (ALD). The transparent substrate was heated to 120°C. Triethylaluminum (TMA) was selected as the reactant. The pulse time was 2s. A N2 / H2 mixture was selected as the reducing agent with a volume ratio of 96:4. The pulse time was 15s. The N2 purging time was 10s per cycle. The cycle was 5 times to obtain an extremely thin aluminum layer with a thickness of 0.9nm. This can effectively improve the overall transmittance of the conductive cathode while reducing its resistivity. S2, Zr- and Ga-doped In2O3 thin films were prepared on an extremely thin aluminum layer using a high-power pulsed magnetron / DC co-sputtering method, with a background vacuum level ≤ 5 × 10⁻⁶. -4 At Pa, the argon flow meter was turned on, and the argon flow rate was 20 sccm. Then, the DC power supply, high-power pulse, and DC negative bias power supply were turned on sequentially. Pre-sputtering was performed for 5 min, and the working gas pressure was adjusted to 0.4 Pa. Ga-doped In2O3 target material was selected, with a Ga2O3 / In2O3 mass ratio of 5%. The sputtering power supply was high-power pulsed magnetron sputtering, with a pulse power of 200 W, a pulse width of 150 μs, a pulse frequency of 100 Hz, and a sputtering time of 20 min. Simultaneously, co-sputtering of a metal Zr target was selected, with a DC power supply, a sputtering power of 40 W, and a sputtering time of 5 min. The negative bias voltage of the DC negative bias power supply connected to the substrate was -75 V, resulting in a Zr- and Ga-doped In2O3 thin film with a thickness of 410 nm. S3. After the sample cools to room temperature, it is transferred to a vacuum annealing furnace with a vacuum degree of 1 Pa, an annealing temperature of 280℃, and an annealing time of 62 min to obtain a low work function transparent conductive cathode.

[0037] This second embodiment is basically the same as the first embodiment, except for the adjustment of process parameters. Specifically: In step S1, a PEN flexible substrate was selected in this embodiment. The ALD process parameters were adjusted as follows: TMA pulse time was 2s, the number of cycles was 5, and the remaining parameters were the same as in Example 1. A very thin aluminum layer with a thickness of approximately 0.9nm was finally obtained.

[0038] In step S2, the magnetron sputtering process parameters in this embodiment are adjusted so that the working gas pressure is set to 0.4 Pa. The high-power pulsed magnetron sputtering power supply has a pulse power of 200 W, and the sputtering time for the Ga-doped In₂O₃ target is 20 min; the DC power supply has a sputtering power of 40 W, and the sputtering time for the Zr target is 5 min. The remaining parameters are the same as in Example 1. A Zr- and Ga-doped In₂O₃ thin film with a thickness of approximately 410 nm is finally obtained.

[0039] In step S3, the annealing process parameters are adjusted to an annealing temperature of 280°C and an annealing time of 62 min. The remaining parameters are the same as in Example 1.

[0040] Performance testing: The low work function transparent conductive cathode prepared in this embodiment was tested, and its work function was 4.17 eV. The average transmittance in the wavelength range of 400~1000nm was 85.5%, and the sheet resistance was 10.3Ω / □.

[0041] Example 3: This embodiment provides another method for preparing a low work function transparent conductive cathode, which specifically includes the following steps: S1. Using PI as the substrate, an aluminum layer is prepared on the substrate using atomic layer deposition equipment. The transparent substrate is heated to 120°C. Triethylaluminum is selected as the reactant. The pulse time is 3s. N2 / H2 mixed gas is selected as the reducing agent. The volume ratio of N2 / H2 mixed gas is 96:4. The pulse time is 15s. The N2 purging time is 10s per cycle. The cycle is 7 times. An extremely thin aluminum layer with a thickness of 1.4nm is obtained, which can effectively improve the overall transmittance of the conductive cathode and reduce its resistivity. S2, Zr and Ga-doped In2O3 thin films were prepared on an extremely thin aluminum layer using a high-power pulsed magnetron / DC co-sputtering method, with a background vacuum degree ≤5×10⁻⁶. -4 At Pa, the argon flow meter was turned on, and the argon flow rate was 20 sccm. Then, the DC power supply, high-power pulse, and DC negative bias power supply were turned on sequentially. Pre-sputtering was performed for 5 min, and the working gas pressure was adjusted to 0.5 Pa. Ga-doped In2O3 target material was selected, with a Ga2O3 / In2O3 mass ratio of 5%. The sputtering power supply was high-power pulsed magnetron sputtering, with a pulse power of 260 W, a pulse width of 150 μs, a pulse frequency of 100 Hz, and a sputtering time of 15 min. Simultaneously, co-sputtering of a metal Zr target was selected, with a DC power supply, a sputtering power of 55 W, and a sputtering time of 4 min. The negative bias voltage of the DC negative bias power supply connected to the substrate was -75 V, resulting in a Zr- and Ga-doped In2O3 thin film with a thickness of 320 nm. S3. After the sample cools to room temperature, it is transferred to a vacuum annealing furnace with a vacuum degree of 1 Pa, an annealing temperature of 330 °C, and an annealing time of 54 min to obtain a low work function transparent conductive cathode.

[0042] This third embodiment is basically the same as the first embodiment, except for the adjustment of process parameters, specifically: In step S1, a PI flexible substrate was selected in this embodiment. The ALD process parameters were adjusted as follows: TMA pulse time was 3s, the number of cycles was 7, and the remaining parameters were the same as in Example 1. A very thin aluminum layer with a thickness of approximately 1.4nm was finally obtained.

[0043] In step S2, this embodiment adjusts the magnetron sputtering process parameters as follows: the working gas pressure is adjusted to 0.5 Pa; the high-power pulsed magnetron sputtering power supply pulse power is 260 W; the sputtering time for the Ga-doped In2O3 target is 15 min; the DC power supply sputtering power is 55 W; and the sputtering time for the Zr target is 4 min. The remaining parameters are the same as in Example 1. Finally, a Zr- and Ga-doped In2O3 thin film with a thickness of approximately 320 nm is obtained.

[0044] In step S3, the annealing process parameters in this embodiment are adjusted to an annealing temperature of 330°C and an annealing time of 54 min. The remaining parameters are the same as in Embodiment 1.

[0045] Performance testing: The low work function transparent conductive cathode prepared in this embodiment was tested, and its work function was 4.18 eV. The average transmittance in the wavelength range of 400~1000nm was 86.4%, and the sheet resistance was 10.8Ω / □.

[0046] Example 4: This embodiment provides another method for preparing a low work function transparent conductive cathode, which specifically includes the following steps: S1. Using PET as the substrate, an aluminum layer is prepared on the substrate using atomic layer deposition equipment. The transparent substrate is heated to 120°C. Triethylaluminum is selected as the reactant. The pulse time is 4s. N2 / H2 mixed gas is selected as the reducing agent. The volume ratio of N2 / H2 mixed gas is 96:4. The pulse time is 15s. The N2 purging time is 10s per cycle. The cycle is 10 times to obtain an extremely thin aluminum layer with a thickness of 2nm. This can effectively improve the overall transmittance of the conductive cathode and reduce its resistivity. S2, Zr and Ga-doped In2O3 thin films were prepared on an extremely thin aluminum layer using a high-power pulsed magnetron / DC co-sputtering method, with a background vacuum degree ≤5×10⁻⁶. -4At Pa, the argon flow meter was turned on, and the argon flow rate was 20 sccm. Then, the DC power supply, high-power pulse, and DC negative bias power supply were turned on sequentially. Pre-sputtering was performed for 5 min, and the working gas pressure was adjusted to 0.3 Pa. Ga-doped In2O3 target material was selected, with a Ga2O3 / In2O3 mass ratio of 5%. The sputtering power supply was high-power pulsed magnetron sputtering, with a pulse power of 150 W, a pulse width of 150 μs, a pulse frequency of 100 Hz, and a sputtering time of 25 min. Simultaneously, co-sputtering of a metal Zr target was selected, with a DC power supply, a sputtering power of 60 W, and a sputtering time of 3 min. The negative bias voltage of the DC negative bias power supply connected to the substrate was -75 V, resulting in a Zr- and Ga-doped In2O3 thin film with a thickness of 500 nm. S3. After the sample cools to room temperature, it is transferred to a vacuum annealing furnace with a vacuum degree of 1 Pa, an annealing temperature of 200 °C, and an annealing time of 70 min to obtain a low work function transparent conductive cathode.

[0047] This fourth embodiment is basically the same as the first embodiment, except for the adjustment of process parameters, specifically: In step S1, a flexible PET substrate was selected in this embodiment. The ALD process parameters were adjusted as follows: TMA pulse time was 4s, the number of cycles was 10, and the remaining parameters were the same as in Example 1. A very thin aluminum layer with a thickness of approximately 2nm was finally obtained.

[0048] In step S2, the magnetron sputtering process parameters in this embodiment are adjusted so that the working gas pressure is set to 0.3 Pa. The high-power pulsed magnetron sputtering power supply has a pulse power of 150 W, and the sputtering time for the Ga-doped In₂O₃ target is 25 min; the DC power supply has a sputtering power of 60 W, and the sputtering time for the Zr target is 3 min. The remaining parameters are the same as in Example 1. A Zr- and Ga-doped In₂O₃ thin film with a thickness of approximately 500 nm is finally obtained.

[0049] In step S3, the annealing process parameters in this embodiment are adjusted to an annealing temperature of 200°C and an annealing time of 70 min. The remaining parameters are the same as in Embodiment 1.

[0050] Performance testing: The low work function transparent conductive cathode prepared in this embodiment was tested, and its work function was 4.16 eV. The average transmittance in the wavelength range of 400~1000nm was 85.1%, and the sheet resistance was 9.8Ω / □.

[0051] Comparative example: To further illustrate the beneficial effects of the present invention, the following comparative example is provided in this embodiment. In the comparative example, transparent glass is selected as the substrate, and a single ITO conductive thin film is prepared using a conventional radio frequency magnetron sputtering process. The specific process is as follows: When the base vacuum degree is ≤ 5×10⁻⁶... -4After Pa, argon gas was introduced at a flow rate of 20 sccm, and the working pressure was adjusted to 0.7 Pa. An ITO ceramic target was selected, and an RF power supply was used with a sputtering power of 200 W and a sputtering time of 15 min, resulting in an ITO film with a thickness of approximately 420 nm. Subsequently, it was vacuum annealed at 400 °C for 30 min.

[0052] like Figure 5 As shown, the work function of the ITO conductive cathode prepared in this comparative example is 4.6 eV, as determined by UPS testing. Due to its high work function, when used as a cathode in a device, it tends to form Schottky contacts rather than ohmic contacts with the active layer, resulting in a large contact barrier at the interface. This hinders the effective transport and extraction of charge carriers, thus reducing device performance. In contrast, the composite conductive cathodes prepared in this embodiment all have work functions below 4.2 eV, significantly improving the interfacial contact characteristics.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A low work function transparent conductive cathode, characterized in that, The device comprises a transparent substrate, an ultrathin aluminum layer, and an indium oxide layer stacked together. The ultrathin aluminum layer is located above the transparent substrate and has a thickness of 0.5 nm to 2 nm. The indium oxide layer is located above the ultrathin aluminum layer and is an indium oxide thin film with a thickness of 200 nm to 500 nm and doped with zirconium and gallium.

2. The low work function transparent conductive cathode according to claim 1, characterized in that: The material of the transparent substrate is selected from glass, polyethylene terephthalate, polyethylene naphthalate, or polyimide.

3. A low work function transparent conductive cathode according to claim 1 or claim 2, characterized in that: In indium oxide thin films doped with zirconium and gallium, the doping atomic ratio of zirconium is 1%-3% and that of gallium is 1%-5%.

4. The low work function transparent conductive cathode according to claim 1, characterized in that: The work function of the transparent conductive cathode is less than 4.2 eV.

5. A method for preparing a low work function transparent conductive cathode according to claim 1 or claim 2, characterized in that: Includes the following steps: Step S1: Provide a transparent substrate and heat the transparent substrate to a preset temperature; Step S2: An extremely thin layer of metallic aluminum is formed by cyclic deposition on the transparent substrate using atomic layer deposition. Step S3: A high-power pulsed magnetron sputtering and DC sputtering co-sputtering method is used to deposit and form an indium oxide thin film doped with zirconium and gallium on the ultra-thin aluminum layer; Step S4: Vacuum annealing is performed on the indium oxide thin film after deposition to obtain a low work function transparent conductive cathode.

6. The method for preparing a low work function transparent conductive cathode according to claim 5, characterized in that: In step S1, the set temperature of the transparent substrate 1 is 120°C; In step S2, triethylaluminum is used as an aluminum source precursor, and the pulse duration of the aluminum source precursor is 1s to 4s. A mixture of nitrogen and hydrogen is used as a reducing agent, and the pulse duration of the reducing agent is 15 seconds. Nitrogen gas was introduced for purging, and the purging time was 10 seconds. The atomic layer deposition process involves 3 to 10 cycles.

7. The method for preparing a low work function transparent conductive cathode according to claim 6, characterized in that: The volume ratio of the nitrogen to hydrogen mixture is 96:

4.

8. The method for preparing a low work function transparent conductive cathode according to claim 5, characterized in that: In step S3, a gallium-doped indium oxide target is connected to a high-power pulsed magnetron sputtering power supply, and a zirconium metal target is connected to a DC power supply for co-sputtering. During the sputtering process, a DC negative bias voltage is applied to the substrate. The mass ratio of gallium oxide to indium oxide in the gallium-doped indium oxide target is 5%.

9. The method for preparing a low work function transparent conductive cathode according to claim 8, characterized in that: The high-power pulsed magnetron sputtering power supply has a pulse power of 150W to 300W, a pulse width of 150μs, and a pulse frequency of 100Hz. The DC power supply has a sputtering power of 30W to 60W, a working gas pressure of 0.3Pa to 0.7Pa, an argon flow rate of 20sccm, a DC negative bias voltage applied to the substrate of -75V, and a total sputtering time of 13 minutes to 31 minutes.

10. The method for preparing a low work function transparent conductive cathode according to claim 5, characterized in that: The process parameters for vacuum annealing in step S4 are: vacuum degree of 1 Pa, annealing temperature of 200℃ to 400℃, and annealing time of 45 minutes to 70 minutes.

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