NiO in solar cells x Hole transport layer, its preparation method, and applications

Abstract

This invention discloses a NiO in a solar cell x A method for fabricating a hole transport layer includes: placing a crystalline silicon substrate in a vacuum reaction chamber of a magnetron sputtering apparatus and heating the crystalline silicon substrate to a reaction temperature; introducing a reaction gas into the vacuum reaction chamber, wherein the oxygen flow rate in the reaction gas changes at a linear rate, so as to grow a NiO layer with a gradually changing bandgap on one side of the crystalline silicon substrate. x Hole transport layer; wherein, NiO x The band gap of the hole transport layer gradually increases from the transparent conductive layer in the solar cell toward the crystalline silicon substrate. The transparent conductive layer is located in NiO. x The hole transport layer is located on the side away from the crystalline silicon substrate to allow NiO to... x The energy band of the hole transport layer near the transparent conductive layer matches the energy band of the transparent conductive layer, and NiO x The energy band of the hole transport layer near the crystalline silicon substrate matches the energy band of the crystalline silicon substrate. The NiO prepared by this invention... x The application of hole transport layers in solar cells can help improve the short-circuit current density and fill factor of solar cells.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a solar cell, and more particularly to a NiO used in a solar cell. x Hole transport layer, its preparation method, and applications. Background Technology

[0002] Crystalline silicon heterojunction solar cells have become a major pillar of the photovoltaic industry due to their high photoelectric conversion efficiency and good stability. Doped amorphous silicon materials, as a commonly used window layer material, have made significant contributions to the development of high-efficiency crystalline silicon heterojunction cells; however, their inherently small bandgap hinders further improvements in photoelectric conversion efficiency. Therefore, it is necessary to find wide-bandgap materials as window layers to reduce parasitic absorption and thus improve device efficiency. Nickel oxide, as a wide-bandgap p-type semiconductor material, has great development potential. NiO x The photoelectric properties of materials are closely related to the number of Ni vacancies within them. By adjusting the O content, the number of Ni vacancies in the thin film can be effectively changed, thereby affecting the transmittance and Fermi level position of the film. NiO x The band structure of thin films greatly affects the performance of solar cell devices. As the oxygen content within the thin film increases, NiO... x The valence band position of the thin film gradually decreases, approaching the valence band position of crystalline silicon to form a smaller valence band gap, which is beneficial for hole transport. However, as the oxygen content increases, the number of Ni vacancies in the thin film increases, the carrier concentration rises, and the backscattering phenomenon of light passing through the thin film becomes more severe. Therefore, the band gap of the thin film decreases with the increase of oxygen content, which seriously hinders the utilization of light and is also a major factor that hinders the improvement of device performance. Summary of the Invention

[0003] In view of this, the present invention provides a NiO in a solar cell. x Hole transport layer, formed by creating a NiO layer with tunable band position gradient. x Thin film, making NiO x The hole transport layer forms a good selective transport structure with the crystalline silicon substrate and a good ohmic contact with the transparent conductive oxide electrode, while also taking into account its optical properties.

[0004] This invention provides a NiO in a solar cell x A method for fabricating a hole transport layer includes: placing a crystalline silicon substrate in a vacuum reaction chamber of a magnetron sputtering apparatus and heating the crystalline silicon substrate to a reaction temperature; introducing a reaction gas into the vacuum reaction chamber, wherein the oxygen flow rate in the reaction gas changes at a linear rate, so as to grow a NiO layer with a gradually changing bandgap on one side of the crystalline silicon substrate. x Hole transport layer; wherein, NiO xThe band gap of the hole transport layer gradually increases from the transparent conductive layer in the solar cell toward the crystalline silicon substrate. The transparent conductive layer is located in NiO. x The hole transport layer is located on the side away from the crystalline silicon substrate to allow NiO to... x The energy band of the hole transport layer near the transparent conductive layer matches the energy band of the transparent conductive layer, and NiO x The energy band of the hole transport layer near the crystalline silicon substrate matches the energy band of the crystalline silicon substrate.

[0005] The present invention also provides a NiO in a solar cell prepared by the above-described preparation method. x Hole transport layer.

[0006] The present invention also provides a NiO in the above-mentioned solar cell. x The application of hole transport layers in solar cells: A solar cell, from bottom to top, comprises: a metal back electrode, an electron transport layer, a first passivation layer, a crystalline silicon substrate, a second passivation layer, and NiO. x Hole transport layer, transparent conductive layer, gate electrode; wherein, NiO x The band gap of the hole transport layer gradually increases from the transparent conductive layer toward the crystalline silicon substrate.

[0007] According to an embodiment of the present invention, NiO is prepared by magnetron sputtering. x Hole transport layer, by adjusting the oxygen-argon flow ratio in the reactant gas, enables the preparation of NiO. x The valence band position of the hole transport layer gradually increases from the transparent conductive layer towards the crystalline silicon substrate, so that NiO x The energy band of the hole transport layer near the crystalline silicon substrate matches the energy band of the crystalline silicon substrate, and makes NiO... x The energy band of the hole transport layer near the transparent conductive layer matches the energy band of the transparent conductive layer, which is beneficial for hole transport; due to NiO x The hole transport layer matches the energy bands of the crystalline silicon substrate and the transparent conductive layer, enabling NiO... x The hole transport layer has a small contact resistance with the transparent conductive layer and the crystalline silicon substrate, which reduces the series resistance of the crystalline silicon heterojunction solar cell, improves the fill factor, and is conducive to obtaining a high-efficiency crystalline silicon heterojunction solar cell.

[0008] NiO provided according to the above embodiments of the present invention x The method for preparing the hole transport layer involves adjusting the argon-oxygen flow ratio in the reaction gas to change the NiO content. x The oxygen-to-nickel ratio in the hole transport layer affects the quality of the prepared NiO. x The band gap of the hole transport layer film gradually increases from the transparent conductive layer to the crystalline silicon substrate, optimizing the NiO band gap. xThe hole transport layer film achieves a balance between light transmittance and band structure and optical properties, reducing optical losses caused by band matching with the crystalline silicon substrate, thus improving the prepared NiO. x The hole transport layer combines the characteristics of wide bandwidth and low contact resistivity. Attached Figure Description

[0009] Figure 1 NiO in a solar cell according to an embodiment of the present invention x Flowchart of the method for preparing the hole transport layer;

[0010] Figure 2 This is a cross-sectional schematic diagram of a solar cell according to an embodiment of the present invention;

[0011] Figure 3 A comparison chart of the JV curves of solar cells in related technologies and solar cells in embodiments of the present invention; and

[0012] Figure 4 c-Si / NiO in related technologies x / ITO contact resistance and c-Si / NiO in embodiments of the present invention x Comparison chart of test results for ITO contact resistance.

[0013] [Explanation of Labels in the Attached Image]

[0014] 1-Metal back electrode;

[0015] 2-Electron transport layer;

[0016] 31 - First passivation layer;

[0017] 32 - Second passivation layer;

[0018] 4-Crystal silicon substrate;

[0019] 5-NiO x Hole transport layer;

[0020] 6-Transparent conductive layer;

[0021] 7-Gate line electrode. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, this invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0024] Figure 1 NiO in a solar cell according to an embodiment of the present invention x A flowchart of the method for preparing a hole transport layer. Figure 2 This is a cross-sectional schematic diagram of a solar cell according to an embodiment of the present invention.

[0025] According to an exemplary embodiment of the present invention, the present invention provides NiO in a solar cell. x For the fabrication method of the hole transport layer, refer to Figure 1 and Figure 2 As shown, it includes steps S01 to S02.

[0026] In step S01, the silicon substrate 4 is placed in the vacuum reaction chamber of the magnetron sputtering equipment, and the silicon substrate 4 is heated to the reaction temperature.

[0027] According to an embodiment of the present invention, the above-described preparation method further includes: before placing the crystalline silicon substrate 4 in the vacuum reaction chamber, forming a first passivation layer 31 and a second passivation layer 32 on both sides of the crystalline silicon substrate 4, respectively, to reduce the impact of the crystalline silicon substrate 4 and NiO. x Interface defects in hole transport layer 5, as well as interface defects between crystalline silicon substrate 4 and electron transport layer 2, thereby reducing carrier recombination at interface defects.

[0028] According to an embodiment of the present invention, the crystalline silicon substrate 4 can be a textured structure or a planar structure.

[0029] According to an embodiment of the present invention, if the crystalline silicon substrate 4 has a textured structure, the above-mentioned preparation method further includes: before forming the first passivation layer 31 and the second passivation layer 32 on both sides of the crystalline silicon substrate 4, respectively, etching the crystalline silicon substrate 4 with an alkaline solution and a texturing agent, the alkaline solution being, for example, a KOH solution, to form a textured structure on the surface of the crystalline silicon substrate 4, thereby forming a light-trapping structure on the surface of the crystalline silicon substrate 4 and improving light utilization.

[0030] According to an embodiment of the present invention, the crystalline silicon substrate 4 is pretreated to obtain a clean crystalline silicon substrate with passivation layers grown on both sides. Specifically, after cleaning the surface of the crystalline silicon substrate 4 with an RCA standard cleaning solution, the surface of the crystalline silicon substrate 4 is etched with an alkaline solution to form a textured structure, and the surface of the crystalline silicon substrate 4 is dried with nitrogen. The dried crystalline silicon substrate 4 is immersed in a 20 wt% H2O2 solution for 30 min to form a first passivation layer 31 and a second passivation layer 32 on both sides of the crystalline silicon substrate 4, wherein the materials of the first passivation layer 31 and the second passivation layer 32 are SiO x . After forming the passivation layers on both sides of the crystalline silicon substrate 4, it is dried with nitrogen to obtain a clean crystalline silicon substrate with passivation layers grown on both sides.

[0031] According to an embodiment of the present invention, NiO is deposited on the side of the second passivation layer 32 away from the crystalline silicon substrate 4 by magnetron sputtering x The device used for the hole transport layer 5 is a radio frequency magnetron sputtering device, and the target used is a high-purity NiO x ceramic target, for example, it can be a NiO x ceramic target with a purity greater than 99.9%; the background vacuum degree of the vacuum reaction chamber is 10 -3 ~10 -4 Pa.

[0032] According to an embodiment of the present invention, the crystalline silicon substrate 4 is heated to a reaction temperature, and the reaction temperature is 100 - 200 °C. The reaction temperature can be, for example, 100 °C, 120 °C, 150 °C, 170 °C, 200 °C.

[0033] In step S02, a reaction gas is introduced into the vacuum reaction chamber, and the oxygen flow rate in the reaction gas changes linearly to grow a NiO x hole transport layer 5 on one side of the crystalline silicon substrate 4.

[0034] According to an embodiment of the present invention, the O2 flow rate in the reaction gas changes linearly according to formula (1):

[0035] F(t) = F0 + Ct (1)

[0036] where, F(t) represents the O2 flow rate at time t, F0 represents the initial O2 flow rate, C represents the linear change rate of the O2 flow rate, and t represents the sputtering duration from the initial introduction time of the reaction gas to time t.

[0037] According to an embodiment of the present invention, the thickness of the NiO x hole transport layer (0 < x < 1.5) is 5 - 40 nm. It should be noted that the O2 flow rate gradually increases from F0 sccm; the sputtering duration t is determined by the required film thickness and the sputtering rate.

[0038] According to an embodiment of the present invention, during the preparation of NiO x for the hole transport layer, the pressure of the reaction gas introduced is 0.2 to 1.0 Pa, and the reaction gas is a mixed gas of Ar and O2; the initial flow ratio of oxygen to argon introduced into the vacuum reaction chamber can be, for example, 4.4%.

[0039] According to an embodiment of the present invention, NiO is deposited on the side of the second passivation layer 32 away from the crystalline silicon substrate 4 by magnetron sputtering. x The crystalline silicon substrate 4 formed with the first passivation layer 31 and the second passivation layer 32 is placed in the vacuum reaction chamber of the magnetron sputtering equipment. After the background vacuum of the reaction chamber is pumped to 3×10 -3 Pa, the crystalline silicon substrate 4 is heated to 150 °C, and a reaction gas including Ar and O2 is introduced. The flow rate of Ar is constant, for example, it can be 18 sccm, while the flow rate of O2 increases linearly. For example, the flow rate of O2 increases from 2 sccm to 4 sccm at a growth rate shown by the formula F(t)=2 + 0.1t, and finally a NiO x hole transport layer 5 with a thickness of about 20 nm is deposited on the second passivation layer 32. Here, F(t) represents the O2 flow rate at time t, and t represents the sputtering duration from the initial introduction time of the reaction gas to time t.

[0040] According to an embodiment of the present invention, by adjusting the argon-oxygen flow ratio in the reaction gas, the oxygen-nickel ratio (i.e., the value of x, 0 < x < 1.5) in the NiO x hole transport layer is changed, so that the valence band energy level range of the NiO x hole transport layer is approximately -5.1 eV to -5.4 eV, and the valence band position of the NiO x hole transport layer 5 gradually increases from the light incident surface (transparent conductive layer 6) to the direction of the crystalline silicon substrate 4, so that the NiO x hole transport layer 5 is energy band matched with the crystalline silicon substrate 4 and the transparent conductive layer 6. The valence band of the crystalline silicon substrate 4 is about -5.17 eV, and the valence band of the ITO transparent conductive layer 6 is about -6.8 eV; the optical band gap is 3.6 eV to 4.0 eV, so as to improve the x light transmittance of the NiO hole transport layer 5. It should be noted that the larger the light transmittance of the NiO x hole transport layer, the smaller the parasitic absorption, the less the absorption of light, and more light can be absorbed by the crystalline silicon substrate 4, improving the short-circuit current density and the fill factor, and further improving the photoelectric conversion efficiency of the solar cell.

[0041] According to an embodiment of the present invention, the sputtering power of magnetron sputtering is 140 to 160 W, for example, it can be 140 W, 145 W, 150 W, 155 W, 160 W.

[0042] The present invention also provides a NiO in a solar cell prepared by the above-described preparation method. x Hole transport layer.

[0043] According to an exemplary embodiment of the present invention, the present invention provides a NiO in the above-described solar cell. x Applications of hole transport layers in solar cells, see reference. Figure 2 As shown, the solar cell, from bottom to top, comprises: a metal back electrode 1, an electron transport layer 2, a first passivation layer 31, a crystalline silicon substrate 4, a second passivation layer 32, and NiO. x Hole transport layer 5, transparent conductive layer 6, gate electrode 7; wherein, NiO x The band gap of the hole transport layer 5 gradually increases from the transparent conductive layer 6 toward the crystalline silicon substrate 4.

[0044] According to an embodiment of the present invention, during the deposition of NiO x After hole transport layer 5 is completed, NiO will be deposited. x The silicon substrate 4 with hole transport layer 5 is placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, and an n-type heavily doped electron transport layer 2 is deposited on the side of the first passivation layer 31 away from the silicon substrate 4. The process is carried out using magnetron sputtering on NiO. x A transparent conductive layer (TCO) 6 is deposited on the hole transport layer 5 as the light incident surface. The TCO can be, for example, ITO (indium tin oxide semiconductor transparent conductive film), and the thickness can be, for example, 80-100 nm.

[0045] According to an embodiment of the present invention, a gate electrode 7 is deposited on the incident light surface using electron beam evaporation. The material of the gate electrode 7 can be, for example, Al, and the thickness can be, for example, 1 μm. A metal back electrode 1 is deposited on the side of the electron transport layer 2 away from the first passivation layer 31. The material of the metal back electrode 1 can be, for example, Al, and the thickness can be, for example, 5000 nm.

[0046] According to an embodiment of the present invention, the solar cell further includes an antireflection layer (not shown in the figure) located between the transparent conductive layer 6 and the grid electrode 7. The material of the antireflection layer may be, for example, SiN. x It is suitable for reducing light reflection.

[0047] It should be noted that n-type crystalline silicon substrate 4 and p-type NiO x Hole transport layer 5 forms a crystalline silicon heterojunction.

[0048] According to embodiments of the present invention, the NiO provided by the present invention xHole transport layers can be applied in crystalline silicon heterojunction solar cells (HJT), as well as in Top-Con (tunneling oxide passivated contact) cells, DASH (doped-free, asymmetric heterojunction) cells, PERC (passivated emitter and back contact), PERL (passivated emitter back local diffusion) or PERT (passivated emitter junction full back field diffusion) cells.

[0049] Figure 3 This is a comparison chart of the JV curves of solar cells in related technologies and solar cells in embodiments of the present invention.

[0050] refer to Figure 3 As shown, the NiO prepared by gradually varying the O2 flow rate from 2 sccm to 4 sccm in this embodiment of the invention... x The open-circuit voltage of solar cells with hole transport layers is higher than that of NiO prepared using O2 flow rates of 2 sccm and 4 sccm. x The open-circuit voltage of a solar cell formed by a hole transport layer; NiO prepared by gradually varying the O2 flow rate from 2 sccm to 4 sccm in this embodiment of the invention. x The short-circuit current density of solar cells with hole transport layers is higher than that of NiO prepared using O2 fluxes of 2 sccm and 4 sccm. x The short-circuit current density of a solar cell formed by a hole transport layer. Here, Voc represents the open-circuit voltage, and Jsc represents the short-circuit current density.

[0051] Figure 4 c-Si / NiO in related technologies x / ITO contact resistance and c-Si / NiO in embodiments of the present invention x Comparison chart of test results for ITO contact resistance.

[0052] refer to Figure 4 As shown, the TLM (Transfer Length Method) was used to detect c-Si / NiO in related technologies. x / ITO contact resistance and c-Si / NiO in embodiments of the present invention x / ITO contact resistance. Test results show that the NiO prepared by gradually varying the O2 flow rate from 2 sccm to 4 sccm in this embodiment of the invention... x c-Si / NiO solar cells with hole transport layers x / ITO contact resistance is less than that of NiO prepared with O2 flow rates of 2 sccm and 4 sccm. x c-Si / NiO solar cells with hole transport layers x / ITO contact resistance. NiO xThe hole transport layer 5 has low contact resistance with the crystalline silicon substrate 4 and the transparent conductive layer 6, which is beneficial for improving the fill factor. Here, the horizontal axis represents O2 flux, and the vertical axis represents c-Si / NiO. x / ITO contact resistance value.

[0053] It should be noted that when light is incident on the solar cell, electron-hole pairs are generated in the crystalline silicon substrate 4. These electron-hole pairs exist between the crystalline silicon substrate 4 and the NiO layer. x Under the influence of the built-in electric field formed by the hole transport layer 5, the holes are separated, the holes are collected by the grid line electrode 7, and the electrons are collected by the metal back electrode 1, thereby generating photocurrent.

[0054] According to an embodiment of the present invention, NiO is prepared by magnetron sputtering. x Hole transport layer, by adjusting the oxygen-argon flow ratio in the reaction gas, to prepare NiO x The valence band position of the hole transport layer gradually increases from the light-incident surface (transparent conductive layer) towards the crystalline silicon substrate, so that NiO... x The energy band of the hole transport layer near the crystalline silicon substrate matches the energy band of the crystalline silicon substrate, and makes NiO... x The energy band of the hole transport layer near the transparent conductive layer matches the energy band of the transparent conductive layer, which is beneficial for hole transport; due to NiO x The hole transport layer matches the energy bands of the crystalline silicon substrate and the transparent conductive layer, enabling NiO... x The hole transport layer has a small contact resistance with the transparent conductive layer and the crystalline silicon substrate, which reduces the series resistance of the crystalline silicon heterojunction solar cell, improves the fill factor, and is conducive to obtaining a high-efficiency crystalline silicon heterojunction solar cell.

[0055] It should be noted that NiO x The smaller the oxygen-to-nickel ratio in the hole transport layer, the better the NiO content. x The wider the band gap of the hole transport layer material, the greater the light transmittance and the smaller the parasitic absorption. The reduced light absorption allows more light to be absorbed by the crystalline silicon substrate, increasing the short-circuit current density of the solar cell and thus improving the photoelectric conversion efficiency of the solar cell.

[0056] NiO provided according to the above embodiments of the present invention x The method for preparing the hole transport layer involves adjusting the argon-oxygen flow ratio in the reaction gas to change the NiO content. x The oxygen-to-nickel ratio in the hole transport layer affects the quality of the prepared NiO. x The band gap of the hole transport layer film gradually increases from the incident light surface to the crystalline silicon substrate, optimizing the NiO band gap. x The hole transport layer film achieves a balance between light transmittance and band structure and optical properties, reducing optical losses caused by band matching with the crystalline silicon substrate, thus improving the prepared NiO. xHole transport layers combine the advantages of wide bandgap and low contact resistivity, making them an ideal choice for hole transport layers in crystalline silicon heterojunction solar cells.

[0057] According to an embodiment of the present invention, a magnetron sputtering method is used to directly react sputtered Ni atoms with O2 in an O2 atmosphere. This method has the characteristics of high activity, complete reaction, and dense film. It also has the characteristics of simple preparation process, good repeatability, low cost, and suitability for large-area production.

[0058] The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify the corresponding elements does not imply that the element has any ordinal number, nor does it represent the order of one element with another element, or the order of manufacturing methods. The use of these ordinal numbers is only to enable a named element to be clearly distinguished from another element with the same name.

[0059] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. NiO in a solar cell x The method for preparing a hole transport layer is characterized in that, include: The crystalline silicon substrate (4) is placed in the vacuum reaction chamber of the magnetron sputtering equipment, and the crystalline silicon substrate (4) is heated to the reaction temperature; A reaction gas is introduced into the vacuum reaction chamber, wherein the oxygen flow rate in the reaction gas varies at a linear rate, so as to grow NiO with a bandgap gradient on one side of the crystalline silicon substrate (4). x Hole transport layer (5); Wherein, the NiO x The band gap of the hole transport layer (5) gradually increases from the transparent conductive layer (6) in the solar cell toward the crystalline silicon substrate (4), and the transparent conductive layer (6) is located on the NiO layer. x The hole transport layer (5) is located on the side away from the crystalline silicon substrate (4) so ​​that the NiO x The energy band of the hole transport layer (5) near the transparent conductive layer (6) matches the energy band of the transparent conductive layer (6), and the NiO x The energy band of the hole transport layer (5) near the crystalline silicon substrate (4) matches the energy band of the crystalline silicon substrate (4).

2. The preparation method according to claim 1, characterized in that, Also includes: Before placing the crystalline silicon substrate (4) in the vacuum reaction chamber, a first passivation layer (31) and a second passivation layer (32) are formed on both sides of the crystalline silicon substrate (4).

3. The preparation method according to claim 2, characterized in that, Also includes: Before forming a first passivation layer (31) and a second passivation layer (32) on both sides of the crystalline silicon substrate (4), the crystalline silicon substrate (4) is etched with an alkaline solution to form a textured surface structure on the surface of the crystalline silicon substrate (4).

4. The preparation method according to claim 1, characterized in that, The background vacuum level of the vacuum reaction chamber is 10. -3 ~10 -4 Pa.

5. The preparation method according to claim 1, characterized in that, The crystalline silicon substrate (4) is heated to the reaction temperature, which is 100-200°C.

6. The preparation method according to claim 1, characterized in that, The pressure of the reactant gas is 0.2–1.0 Pa; The reacting gas is a mixture of Ar and O2.

7. The preparation method according to claim 1, characterized in that, NiO growth x The sputtering power of the hole transport layer (5) is 140-160W.

8. The preparation method according to claim 1, characterized in that, Growth of NiO x The target material used in the hole transport layer (5) is NiO with a purity greater than 99.9%. x Ceramic target.

9. A NiO in a solar cell prepared by the preparation method according to any one of claims 1 to 8 x Hole transport layer.

10. A NiO in a solar cell as described in claim 9 x The application of hole transport layers in solar cells is characterized by, The solar cell, from bottom to top, comprises: a metal back electrode (1), an electron transport layer (2), a first passivation layer (31), a crystalline silicon substrate (4), a second passivation layer (32), and NiO. x Hole transport layer (5), transparent conductive layer (6), gate electrode (7); Wherein, the NiO x The band gap of the hole transport layer (5) gradually increases from the transparent conductive layer (6) toward the crystalline silicon substrate (4).

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