High-performance photoelectrocatalytic silicon photocathode and preparation method thereof

Abstract

The application belongs to the technical field of photoelectrocatalytic water decomposition, and particularly relates to a high-performance photoelectrocatalytic silicon photocathode and a preparation method thereof. x The passivation layer film, the Nb2O5 electron transport layer film and the Pt:CeO2 catalytic layer film are prepared by sequentially adopting a chemical oxidation method and an electron beam evaporation deposition system. In the preparation process, the energy band structure of the material is finely adjusted by controlling the deposition thickness of the Nb2O5 film in the electron beam evaporation deposition system, so that a good heterojunction is formed with the p-Si, the generation of a larger photovoltage on the p-Si photocathode is promoted, and the photoelectrocatalytic water decomposition performance of the p-Si photocathode is significantly improved. Compared with the prior art, the Nb2O5 electron transport layer in the application not only can protect the p-Si from being corroded in an alkaline environment and improve the service life of the p-Si photocathode, but also can solve the problem of energy band structure matching and improve the photoelectrochemical water decomposition efficiency of the p-Si photocathode.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalytic water splitting technology, specifically relating to a high-performance photoelectrocatalytic silicon photocathode and its preparation method. Background Technology

[0002] With the excessive consumption of non-renewable energy and the increasing severity of environmental problems globally, the demand for renewable and clean energy is becoming increasingly urgent. Among numerous renewable energy sources, solar energy, due to its wide availability, strong sustainability, and outstanding environmental friendliness, is considered one of the important pathways to address the energy crisis, alleviate environmental pollution, and promote low-carbon transformation. Hydrogen energy, with its advantages such as high energy density and zero carbon emissions, has become a key component of clean energy systems. Converting solar energy into hydrogen energy through photoelectrochemistry (PEC) water splitting is currently a widely recognized and promising sustainable energy conversion method.

[0003] The core of photoelectrochemical water splitting lies in semiconductor photoelectrodes. Among many semiconductor materials, silicon (Si) is an ideal choice for photocathode materials due to its abundance in the Earth's crust, mature preparation technology, and suitable band gap (approximately 1.12 eV), which allows it to effectively absorb visible light. Under illumination, silicon absorbs photons with energy greater than or equal to its band gap, generating photogenerated electron-hole pairs. The photogenerated electrons migrate to the electrode surface to participate in the hydrogen evolution reaction (HER), thereby realizing the conversion of solar energy into hydrogen energy.

[0004] However, the practical application of silicon-based photocathodes still faces many challenges. Due to recombination losses of photogenerated charges during cross-interface transport, sluggish surface reaction kinetics, and poor bandgap matching between silicon and the catalyst layer, the photoelectric conversion efficiency (such as photocurrent density and onset potential) of current silicon-based photocathodes is still far below the theoretical limit, making it difficult to meet the practical needs of efficient and low-cost solar hydrogen production.

[0005] To improve the performance of silicon photocathodes, researchers have conducted extensive optimization work. One of the current mainstream strategies is to construct an embedded electric field on the silicon surface to promote the separation of photogenerated carriers. For example, in 2011, Lewis's group constructed a pn homojunction by doping phosphorus on the surface of p-type silicon (p-Si) to form an n⁺ emitter layer, effectively increasing the onset potential of the photocathode (Boettcher SW, Warren EL, Putnam MC, et al. Photoelectrochemical Hydrogen Evolution Using Si Microwire Arrays[J]. Journal of the American Chemical Society, 2011, 133(5): 1216-1219.). Besides homojunctions, constructing heterojunctions by introducing wide-bandgap semiconductor materials has also been proven to be an effective way to improve carrier separation efficiency (Yu C, Jia Q, Zhang H, et al. Enhancing photoelectrochemical hydrogen production of an + p-Si heterojunction photocathode with amorphous Ni and Ti layers[J]. Inorganic Chemistry Frontiers, 2019, 6(2): 527-532.). Currently, p-Si heterojunction photocathodes constructed based on materials such as TiO2 and Ta2O5 have improved the water splitting performance of PEC to some extent, but their photoelectric conversion efficiency is still limited by problems such as high interface defect state density and poor band matching, and the overall performance has not yet achieved a breakthrough.

[0006] Therefore, how to further optimize the structural design of silicon photocathodes, improve the separation and transport characteristics of photogenerated carriers, and enhance interfacial reaction dynamics remains a key issue that needs to be addressed in current research. Summary of the Invention

[0007] The purpose of this invention is to provide a high-performance photocatalytic silicon photocathode and its preparation method, so as to solve the problems of severe photogenerated carrier recombination loss and low onset potential caused by poor interface band matching and simple carrier transport layer structure in existing silicon-based photocathodes.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a high-performance photocatalytic silicon photocathode includes the following steps:

[0010] Step 1: Clean and etch the p-type silicon substrate;

[0011] Step 2: Growing SiO2 on the p-type silicon substrate treated in Step 1 using a chemical oxidation method. x passivation layer;

[0012] Step 3: An Nb2O5 electron transport layer is prepared on the structure obtained in Step 2 using electron beam deposition. The deposition thickness is controlled to be 50-200 nm to form a heterojunction with reduced conduction band offset between the Nb2O5 electron transport layer and the p-type silicon substrate.

[0013] Step 4: A Pt-doped CeO2 catalyst layer is prepared on the structure obtained in Step 3 using a dual-source electron beam deposition method, and the deposition thickness ratio of Pt to CeO2 is controlled to be 0.4 to 0.6:1.

[0014] Step 5: Process the back side of the structure obtained in Step 4 and fabricate electrodes to obtain a high-performance photocatalytic silicon photocathode.

[0015] Furthermore, the operation process of step 1 includes:

[0016] The p-type silicon substrate was ultrasonically cleaned with acetone and isopropanol in sequence, dried with nitrogen, and then etched with 0.5-2% HF solution for 0.5-2 min.

[0017] Furthermore, the operation process of step 2 includes:

[0018] A mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 2.5–3.5:1 was prepared. The p-type silicon substrate treated in step 1 was placed in the mixed solution and treated at 20–30°C for 10–14 hours. After the reaction, the substrate was washed with deionized water and dried with nitrogen gas to obtain a SiO2-coated substrate. x p-Si structure of passivation layer.

[0019] Furthermore, the implementation process of step 3 includes:

[0020] The substrate treated in step 2 is placed in an electron beam deposition system and evacuated to a vacuum level of ≤5×10⁻⁻. 6 Torr deposits Nb2O5 at a rate of 1–5 Å / s to a thickness of 50–200 nm.

[0021] Furthermore, the implementation process of step 4 includes:

[0022] The sample processed in step 3 was placed in a dual-source electron beam deposition system and evacuated to a vacuum level of ≤5×10⁻⁻. 6Torr deposited Pt at a rate of 0.1 Å / s and CeO2 at a rate of 0.2 Å / s, resulting in a Pt to CeO2 deposition thickness ratio of 0.4 to 0.6:1.

[0023] Furthermore, the implementation process of step 5 includes:

[0024] The back side of the structure obtained in step 4 was etched with a 4-6% HF solution for 0.5-2 minutes and then rinsed with deionized water.

[0025] Indium-gallium liquid alloy is coated onto the etched back side;

[0026] Conductive silver paste is used to connect the wires to the back side coated with indium-gallium liquid alloy;

[0027] The connection is encapsulated and covered with epoxy resin to form an ohmic contact.

[0028] A high-performance photocatalytic silicon photocathode is prepared by the above-described method; it comprises a p-type silicon substrate and SiO2 formed sequentially from bottom to top. x The passive layer, the Nb₂O₅ electron transport layer, and the Pt-doped CeO₂ catalytic layer are characterized by:

[0029] The thickness of the Nb2O5 electron transport layer is 50-200 nm, and a heterojunction with reduced conduction band offset is formed between it and the p-type silicon substrate.

[0030] The thickness ratio of Pt to CeO2 in the Pt-doped CeO2 catalyst layer is 0.4–0.6:1; Pt is uniformly doped in the CeO2 matrix. This is used to lower the energy barrier of the hydrogen evolution reaction, improve conductivity and stability, and simultaneously achieve highly efficient photoelectrocatalysis in synergy with the Nb2O5 electron transport layer.

[0031] Furthermore, the Nb₂O₅ electron transport layer is a uniform and dense thin film layer that has a +5 niobium chemical state and does not contain Nb. 4+ Defective state.

[0032] Furthermore, an indium-gallium liquid alloy layer, a conductive silver paste layer, and an epoxy resin encapsulation layer are sequentially formed on the back side of the p-type silicon substrate to form an ohmic contact.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. Significantly improves the photoelectric conversion efficiency and output photovoltage of the photocathode. This invention achieves this by sequentially constructing SiO2 on the p-Si surface. xA passivation layer, an Nb₂O₅ electron transport layer, and a Pt:CeO₂ catalytic layer were used to construct a structurally complete and functionally synergistic photocathode system. The thickness of the Nb₂O₅ electron transport layer can be precisely controlled during electron beam evaporation deposition, thereby achieving fine modulation of the material's band structure and ensuring a good bandgap match with the p-Si substrate, thus constructing a high-quality heterojunction. This structure effectively promotes the separation and transport of photogenerated carriers, significantly suppresses interfacial recombination losses, and enables the p-Si photocathode to generate a larger photovoltage under illumination, thereby greatly improving its photoelectrochemical water splitting performance.

[0035] 2. Effectively improves the operational stability and service life of the photocathode. The Nb₂O₅ electron transport layer used in this invention not only possesses excellent bandgap matching characteristics but also exhibits good chemical stability. It can serve as an effective protective layer in alkaline electrolyte environments, preventing corrosion of the p-Si substrate. This structural design significantly extends the service life of the p-Si photocathode while improving the photoelectrochemical water splitting efficiency, providing crucial assurance for its practical application.

[0036] 3. This invention achieves controllable fabrication of the interface band structure, solving the key problem of difficult band matching between the electron transport layer and the silicon substrate in existing technologies. By precisely controlling the deposition thickness of the Nb2O5 thin film, this invention enables repeatable and designable fine-tuning of the band structure at the heterojunction interface, overcoming the limitations of traditional materials such as TiO2 and Ta2O5 in band matching, and providing a new technical path for the construction of high-performance silicon-based photocathodes.

[0037] In summary, this invention constructs SiO x The / Nb2O5 / Pt:CeO2 multilayer composite structure enables precise control of the band structure of the Nb2O5 electron transport layer, effectively solving the problems of severe photogenerated charge recombination loss and low onset potential caused by poor interface band matching and simple carrier transport layer structure in existing silicon-based photocathodes. Attached Figure Description

[0038] Figure 1 This is a flowchart of the high-performance photocatalytic silicon photocathode preparation method of the present invention;

[0039] Figure 2 p-Si / SiO x SEM images of the surface of the Nb2O5 sample;

[0040] Figure 3 XPS characterization of Nb2O5 thin films prepared by electron beam evaporation deposition system;

[0041] Figure 4 Characterization of the UPS band structure of Nb2O5 thin films;

[0042] Figure 5 p-Si / SiO x Band structure of the Nb2O5 sample;

[0043] Figure 6 This is a performance diagram of water splitting in a p-Si photocathode PEC, where a represents Pt:CeO2 / Nb2O5 / SiO2. x JV curves of / p-Si photocathodes, b is the ABPE curve corresponding to the JV curve in a, and c is the curve of Pt:CeO2 / Nb2O5 / SiO2. x / p-Si photocathode steady-state photocurrent test curve. Detailed Implementation

[0044] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0045] This invention provides a method for preparing high-performance photocatalytic silicon photocathodes, which utilizes chemical oxidation and electron beam evaporation deposition to prepare SiO on a p-Si substrate. x A passivation layer and an Nb₂O₅ thin film are used to achieve good band structure matching with p-Si, while the excellent protective effect of Nb₂O₅ increases the lifetime of the p-Si photocathode. The process flow is as follows: Figure 1 As shown, the effectiveness of the above preparation method will be verified through specific embodiments below, and the detailed process parameters of each step will be clarified.

[0046] Example 1: Pt:CeO2 / Nb2O5 / SiO x The fabrication of p-Si photocathodes, specifically:

[0047] Step 1.1: Cleaning and etching of p-type silicon substrate: In this embodiment, a p-type silicon (p-Si) single crystal wafer is selected as the substrate. The p-type silicon is ultrasonically cleaned in acetone and isopropanol for 20 minutes each to remove surface oil and organic residues, and then dried with high-purity nitrogen gas.

[0048] Step 1.2: The substrate is then immersed in a 1% hydrofluoric acid (HF) aqueous solution and etched at room temperature for 1 minute to remove the natural oxide layer on the surface. After removal, it is rinsed with deionized water and dried again with nitrogen gas to obtain a clean p-Si substrate.

[0049] Step 2: SiO x Preparation of the passivation layer: The p-Si substrate treated in step 1 was immersed in a mixed solution of concentrated sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) with a volume ratio of 3:1, and treated at 25°C for 12 hours. After the reaction, the substrate was removed, repeatedly rinsed with deionized water to remove residual solution from the surface, and dried with nitrogen gas to obtain a SiO2-coated surface. x The p-Si structure of the passivation layer is denoted as SiO.x / p-Si.

[0050] Step 3: Preparation of the Nb2O5 electron transport layer: The SiO2 obtained in step 2 is... x The p-Si substrate was placed on the sample stage of the electron beam evaporation deposition system, using high-purity Nb2O5 particles as the evaporation source. The deposition chamber was evacuated to a vacuum level ≤5×10⁻⁻. 6 Torr was then used to evaporate Nb₂O₅ at a deposition rate of 1 Å / s, controlling the deposition thickness to 100 nm. After deposition, Nb₂O₅ / SiO₂ was obtained. x / p-Si composite structure.

[0051] Step 4: Preparation of the Pt:CeO2 catalyst layer: The composite structure obtained in Step 3 was placed on the sample stage of a dual-source electron beam evaporation deposition system. High-purity Pt and CeO2 were used as evaporation sources, respectively, and placed in different crucibles. The chamber was evacuated to a vacuum degree ≤5×10⁻⁻⁻⁶. 6 After torsion, two evaporation sources were simultaneously activated, controlling the deposition rate of Pt to 0.1 Å / s and CeO2 to 0.2 Å / s, depositing 25 Å and 50 Å of Pt respectively, achieving a thickness ratio of 0.5:1, thus achieving uniform Pt doping in the CeO2 matrix. After deposition, a Pt:CeO2 / Nb2O5 / SiO2 matrix was obtained. x / p-Si precursor structure.

[0052] Step 5: Backside Electrode Fabrication: The backside of the precursor structure obtained in Step 4 was etched using a 5% HF solution at room temperature for 1 minute to remove any possible oxide layer. After removal, it was rinsed with deionized water and dried with nitrogen. An indium-gallium (In-Ga) liquid alloy was uniformly coated onto the etched backside to form an ohmic contact layer. Copper wires were then connected to the alloy layer using conductive silver paste. Finally, the wire connections were encapsulated with epoxy resin to obtain Pt:CeO2 / Nb2O5 / SiO2. x / p-Si photocathode.

[0053] Example 2: Comparative Example (without Nb2O5 electron transport layer)

[0054] This comparative example is used to verify the key role of the Nb2O5 electron transport layer. Its preparation steps are basically the same as in Example 1, except that: after step 2, step 3 (Nb2O5 electron transport layer preparation) is omitted, and the Nb2O5 electron transport layer is directly prepared on SiO2. x Step 4 involves the preparation of a Pt:CeO2 catalyst layer on the / p-Si surface. Subsequent steps 4 and 5 are the same as in Example 1, ultimately yielding a Pt:CeO2 / SiO2 / SiO2 catalytic layer. x / p-Si photocathode.

[0055] Performance Tests and Results:

[0056] 1. Material characterization:

[0057] Materials characterization was performed on the products at each stage of the preparation process in Example 1 and the final photocathode:

[0058] Morphological characterization: Scanning electron microscopy (SEM) observation showed that the Nb2O5 film prepared in step 3 had a uniform and dense surface without cracks or pores, indicating that the electron beam evaporation deposition process has good film quality.

[0059] Chemical characterization: X-ray photoelectron spectroscopy (XPS) analysis showed that Nb in the Nb₂O₅ thin film was in the +5 oxidation state, and no Nb was detected. 4 The defect state signal indicates that the prepared Nb2O5 thin film has accurate stoichiometry and low defect density.

[0060] Band structure characterization: The band structure diagram constructed by combining ultraviolet photoelectron spectroscopy (UPS) with XPS analysis shows that a heterojunction is formed between Nb2O5 and p-Si, which reduces the conduction band offset. This structure is beneficial for reducing the conduction band barrier and improving the interfacial transport efficiency of photogenerated carriers, thereby promoting the photovoltage (V). ph The generation of ).

[0061] 2. Photoelectrochemical performance testing:

[0062] Using a standard three-electrode system, under simulated sunlight irradiation (AM 1.5G, 100mW / cm²), 2 The photocathodes prepared in Examples 1 and 2 were subjected to photoelectrochemical water splitting performance tests, with 1M KOH solution as the electrolyte.

[0063] The test results are as follows:

[0064] Photocurrent density: The photocathode fabricated in Example 1 achieved a photocurrent density of 30 mA·cm² at 0 V vs. RHE potential. -2 (Please enter specific values), significantly higher than 10 mA·cm in Example 2. -2 .

[0065] Initial potential: The initial potential of the photocathode in Example 1 was 0.42 V vs. RHE, which was shifted by 0.32 V in the positive direction compared to Example 2.

[0066] Photoelectric conversion efficiency: The maximum photoelectric conversion efficiency (ABPE) of the photocathode in Example 1 reached 2.7%.

[0067] Stability test: Under continuous illumination at 0.1 V vs. RHE potential, the photocathode of Example 1 remained stable for 90 hours with no significant decrease in photocurrent density; while under the same test conditions, the photocurrent density of Example 2 decreased significantly in a short period of time.

[0068] Figure 2 This is a SEM image of the surface morphology of the p-Si sample. From... Figure 2 Nb2O5 / SiO can be clearly observed. x The surface morphology of the p-Si sample indicates the uniformity of the thin film prepared by the electron beam evaporation equipment.

[0069] Figure 3 XPS characterization of Nb₂O₅ thin films prepared using an electron beam evaporation apparatus. Figure 3 As shown in (a) and (b), the Nb valence state of the Nb2O5 thin film prepared by electron beam evaporation is +5, and no defective Nb valence state is generated. 4+ .

[0070] Figure 4 Characterization of the UPS band structure of Nb₂O₅ thin films. (From...) Figure 4 It can be seen that the Fermi level of the Nb₂O₅ thin film prepared by electron beam evaporation is -3.94 eV, the conduction band is -3.50 eV, and the valence band is -7.42 eV (relative to the vacuum level).

[0071] Figure 5 p-Si / SiO x Band structure diagram of the Nb₂O₅ sample. Figure 5 It is known that there is a large Fermi level difference between Nb₂O₅ and p-Si. When they come into contact, the potential barrier between the conduction bands of Nb₂O₅ and p-Si is lowered, increasing the carrier transport efficiency and thus increasing the higher photovoltage (V) of the p-Si photocathode under illumination. ph The generation of ) ultimately reduces the applied bias voltage that causes the water reduction reaction, thereby increasing the turn-on voltage of the p-Si photocathode.

[0072] Figure 6 The diagram shows the performance of the p-Si photocathode PEC in water splitting. Figure 6 As shown in (a) to (c), the introduction of the Nb2O5 electron transport layer increases the carrier transport efficiency, significantly improves the PEC water splitting performance of the p-Si photocathode, and also increases the lifetime of the p-Si photocathode. x The / p-Si photocathode ABPE achieves an efficiency of 2.7% and a stability of 90 hours at 0.1V vs. RHE.

[0073] As described above, this invention constructs Pt:CeO2 / Nb2O5 / SiO x A high-performance photocatalytic silicon photocathode was successfully fabricated using a p-Si multilayer composite structure. The core of this structure lies in the introduction of Nb₂O₅ as an electron transport layer onto a p-Si substrate using electron beam evaporation deposition. Nb₂O₅ not only forms a good bandgap match with p-Si, effectively promoting the separation and transport of photogenerated carriers, but also significantly reduces interfacial recombination losses. Simultaneously, this layer, with its excellent protective properties, greatly improves the operational stability of the photocathode. Ultimately, the prepared Pt:CeO₂ / Nb₂O₅ / SiO₂ composite structure... x The p-Si photocathode exhibited superior photoelectrocatalytic water splitting performance.

[0074] It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes can be made to these features and embodiments without departing from the spirit and scope of this invention. Non-essential improvements and adjustments made to this invention by those skilled in the art based on the content of this invention should still fall within the protection scope of this invention.

Claims

1. A method for preparing a high-performance photocatalytic silicon photocathode, characterized in that, Includes the following steps: Step 1: Clean and etch the p-type silicon substrate; Step 2: Growing SiO2 on the p-type silicon substrate treated in Step 1 using a chemical oxidation method. x passivation layer; Step 3: An Nb2O5 electron transport layer is prepared on the structure obtained in Step 2 using electron beam deposition. The deposition thickness is controlled to be 50-200 nm to form a heterojunction with reduced conduction band offset between the Nb2O5 electron transport layer and the p-type silicon substrate. Step 4: A Pt-doped CeO2 catalyst layer is prepared on the structure obtained in Step 3 using a dual-source electron beam deposition method, and the deposition thickness ratio of Pt to CeO2 is controlled to be 0.4 to 0.6:

1. Step 5: Process the back side of the structure obtained in Step 4 and fabricate electrodes to obtain a silicon photocathode.

2. The preparation method according to claim 1, characterized in that, The operation process of step 1 includes: The p-type silicon substrate was ultrasonically cleaned with acetone and isopropanol in sequence, dried with nitrogen, and then etched with 0.5-2% HF solution for 0.5-2 min.

3. The preparation method according to claim 1, characterized in that, The operation process of step 2 includes: Prepare a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 2.5–3.5:

1. Immerse the p-type silicon substrate treated in step 1 in the mixed solution and treat it at 20–30°C for 10–14 hours. After the reaction is complete, wash with deionized water and dry with nitrogen to obtain a surface-coated SiO2. x p-Si structure of passivation layer.

4. The preparation method according to claim 1, characterized in that, The implementation process of step 3 includes: The substrate treated in step 2 is placed in an electron beam deposition system and evacuated to a vacuum level of ≤5×10⁻⁻. 6 Torr deposits Nb2O5 at a rate of 1–5 Å / s to a thickness of 50–200 nm.

5. The preparation method according to claim 1, characterized in that, The implementation process of step 4 includes: The sample processed in step 3 was placed in a dual-source electron beam deposition system and evacuated to a vacuum level of ≤5×10⁻⁻⁻⁻⁻⁴ ... 6 Torr deposited Pt at a rate of 0.1 Å / s and CeO2 at a rate of 0.2 Å / s, resulting in a Pt to CeO2 deposition thickness ratio of 0.4 to 0.6:

1.

6. The preparation method according to claim 1, characterized in that, The implementation process of step 5 includes: The back side of the structure obtained in step 4 was etched with a 4-6% HF solution for 0.5-2 minutes and then rinsed with deionized water. Indium-gallium liquid alloy is coated onto the etched back side; Conductive silver paste is used to connect the wires to the back side coated with indium-gallium liquid alloy; The connection is encapsulated and covered with epoxy resin to form an ohmic contact.

7. A high-performance photocatalytic silicon photocathode, prepared by the method described in any one of claims 1 to 5; comprising a p-type silicon substrate and SiO2 formed sequentially from bottom to top. x The passive layer, the Nb₂O₅ electron transport layer, and the Pt-doped CeO₂ catalytic layer are characterized by: The thickness of the Nb2O5 electron transport layer is 50-200 nm, and a heterojunction with reduced conduction band offset is formed between it and the p-type silicon substrate. The thickness ratio of Pt to CeO2 in the Pt-doped CeO2 catalyst layer is 0.4 to 0.6:1; Pt is uniformly doped in the CeO2 matrix. It can be used to lower the energy barrier of hydrogen evolution reaction, improve conductivity and stability, and achieve efficient photoelectrocatalysis in synergy with Nb2O5 electron transport layer.

8. The silicon photocathode according to claim 7, characterized in that, The Nb₂O₅ electron transport layer is a uniform and dense thin film layer with a +5 niobium chemical state and does not contain Nb. 4+ Defective state.

9. The silicon photocathode according to claim 7, characterized in that, An indium-gallium liquid alloy layer, a conductive silver paste layer, and an epoxy resin encapsulation layer are sequentially formed on the back side of the p-type silicon substrate to form an ohmic contact.

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