CdTe-based high-efficiency laminated solar cell structure and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, and discloses a CdTe-based efficient laminated solar cell structure and a preparation method thereof.The cell structure comprises a substrate, a first transparent conductive layer formed on the substrate, a buffer layer formed on the first transparent conductive layer, a first light absorption layer formed on the buffer layer, and a back contact layer formed on the first light absorption layer, a cadmium telluride sub-battery is obtained; and forming a second transparent conductive layer on the back contact layer, forming a hole transport layer on the second transparent conductive layer, and forming a second light absorption layer on the hole transport layer to obtain the perovskite sub-cell. According to the TCO layer, the SnO2 energy band is optimized through nitrogen ion implantation, the first light absorption layer is doped with Cl and As in a gradient mode, the service life of carriers is prolonged, the unijunction efficiency is larger than 23%, and the lamination efficiency is larger than 31%. The full-dry process is suitable for industrial production of the glass substrate and is suitable for a high-reliability scene.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a CdTe-based high-efficiency tandem solar cell structure and a preparation method thereof. Background Art

[0002] Thin-film solar cells are new photovoltaic devices for alleviating the energy crisis, and different materials such as inexpensive ceramics, graphite, and metal sheets can be used as substrates for manufacturing. Against the background of the continuous shortage of silicon raw materials in the international market, thin-film solar cells have become a new trend and hotspot in the development of the international photovoltaic market. Among them, cadmium telluride thin-film solar cells, abbreviated as CdTe cells, are a kind of compound semiconductor thin-film solar cell with CdTe as the light absorption layer, having a band gap of 1.2 - 1.3 eV, a very high absorption coefficient in the visible light wavelength range (600 nm - 1000 nm), high conversion efficiency, and low cost. Pure inorganic perovskite thin-film solar cells are a kind of thin-film solar cell with an organometallic halide semiconductor as the absorption layer, having a band gap of 1.6 - 1.7 eV and a very high absorption coefficient in the short wavelength band (250 - 700 nm).

[0003] Traditional solar thin-film cells are generally single-layered. In the past few years, many manufacturers have used the tandem technology to prepare amorphous silicon thin-film cells, but the amorphous silicon thin-film cells have a serious S-W effect, which cannot be fundamentally solved. In the process of large-area preparation of traditional single-layer thin-film cells such as cadmium telluride, copper indium gallium selenide, gallium arsenide, perovskite, etc., the efficiency improvement is relatively slow, and some main problems are faced: (1) Conduction band offset problem of the SnO2 buffer layer in CdTe cells: There is a 0.3 eV negative offset between the conduction band bottom of unmodified SnO2 (~4.2 eV) and the conduction band bottom of the CdSeTe absorption layer (~4.5 eV), resulting in interface electron accumulation, and the recombination rate reaches 1×10 4 cm / s (verified by TRPL test), restricting the increase of Voc, and Voc < 900 mV; (2) CdTe material defects: Te vacancies (V_Te) and Cd interstitials (Cd_i) form deep-level recombination centers, and the carrier lifetime < 10 ns (calculated by the quasi-Fermi level splitting model); (3) High-temperature process defects: Traditional close-spaced sublimation (CSS) deposition requires 500 - 600 °C, inducing the Te vacancy concentration in the CdTe lattice > 1×10 16 cm -3, and the Sn diffusion depth at the SnO2 / CdTe interface at high temperature is >50 nm (verified by SIMS test Solar Energy Materials and Solar Cells, 2021); (4) Compatibility defects of stacked integration: Mechanical stacking leads to a photocurrent loss of 12-18%, while the perovskite precursor solution (such as DMF) in monolithic integration corrodes the CdTe surface, and the roughness increases to >20 nm (AFM verification); (5) Back contact Cu diffusion aggravates leakage current: The Cu diffusion rate along the CdTe grain boundary is 3 orders of magnitude higher than that inside the crystal. When the Cu concentration in the junction area is >1×10 17 cm -3 When , the dark current density increases by 2 orders of magnitude (JV curve fitting).

[0004] Patent US9685218B2 uses CdCl2 annealing (400℃, 20 min) to passivate the grain boundaries, but does not solve the band offset problem, and Voc is limited to 850-880 mV. Patent CN110993214A proposes a ZnTe:Cu back contact layer, but due to the valence band offset between ZnTe and CdTe (~0.4 eV), the hole extraction efficiency is less than 70%. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a CdTe-based high-efficiency laminated solar cell structure and its preparation method, which optimizes the SnO2 energy band through nitrogen ion implantation, increases the carrier lifetime through gradient doping, and relieves stress through quantum dot superlattice, so as to achieve single junction efficiency > 23% and laminate efficiency > 31%. The all-dry process is suitable for industrial production of glass substrates and is suitable for high reliability scenarios.

[0006] To achieve this technical purpose, the present invention adopts the following scheme: A method for preparing a CdTe-based high-efficiency tandem solar cell, preparing a cadmium telluride sub-cell on a substrate, and preparing a perovskite sub-cell on the cadmium telluride sub-cell, specifically comprising the following steps: S1. Provide a substrate and pre-treat the substrate; S2, depositing the FTO layer on the substrate by magnetron sputtering process, and then implanting nitrogen ions to optimize the SnO2 energy band to form the first transparent conductive layer (TCO); S3, growing CdSe on the first transparent conductive layer by using a close space sublimation method (CSS) to form a buffer layer; S4, depositing CdTe on the buffer layer by close-space sublimation method, and gradiently doping Cl and As along the growth direction to form a first light absorption layer; S5, depositing ZnTe:Cu on the first light absorption layer by a magnetron sputtering process, and performing laser annealing to form a back contact layer; S6. Deposit SnO2:Sb on the back contact layer by magnetron sputtering to form a second transparent conductive layer; S7. Deposit CuCrO2:Mg on the second transparent conductive layer by reactive sputtering to form a hole transport layer; S8. Deposit perovskite on the hole transport layer by molecular beam epitaxy and synchronously inject PFDA vapor for passivation to form a second light absorption layer.

[0007] Furthermore, the preferred solution of the present invention is: A preparation method of a CdTe-based high-efficiency tandem solar cell. A cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell, specifically including the following steps: S1. Provide a substrate and perform pretreatment on the substrate for mechanical support and light transmission; in this application, the substrate is soda-lime glass (3 mm), which is ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes each in sequence, and then dried with nitrogen for standby.

[0008] S2. Deposit an FTO layer with a thickness of 400 - 550 nm (FTO, fluorine-doped tin oxide) on the substrate by magnetron sputtering, with a sheet resistance of 9 - 12 Ω / sq and a substrate temperature of 400 °C; then perform nitrogen ion implantation to optimize the energy band of SnO2 to form a first transparent conductive layer (TCO); the nitrogen ion implantation energy is 50 - 100 keV, and the dose is 1×10 15 ~5×10 16 cm -2 , the vacuum degree is 10 -6 Torr, and the implantation depth is 10 - 30 nm.

[0009] Through X-ray photoelectron spectroscopy (XPS) analysis, the work function of SnO2 after nitrogen ion implantation modification is increased to 5.075 eV, and the interface recombination rate is reduced to 5×10 3 cm / s; the theoretical basis is: density functional theory (DFT) calculation shows that N doping introduces oxygen vacancy compensation, the conduction band edge moves down by 0.15 eV, and the energy band matching is optimized.

[0010] The first transparent conductive layer (TCO) collects current as the electrode of the battery, and N ion implantation optimizes the energy band matching with CdTe.

[0011] S3. Grow CdSe on the first transparent conductive layer by close-spaced sublimation to form a buffer layer; during the growth of CdSe, O2 (2% - 5%) doping is introduced, the substrate temperature is 300 °C, and a CdSe layer with a thickness of 120 - 180 nm is deposited, and its interface recombination velocity < 10 3 cm / s.

[0012] The buffer layer can reduce the lattice mismatch at the CdTe / TCO interface, and O doping can passivate surface states and reduce the interface recombination rate.

[0013] S4. Deposit CdTe on the buffer layer by close-spaced sublimation method, and perform gradient doping of Cl (5×10 18 →1×10 17 cm -3 ), As (1×10 17 cm -3 ) along the growth direction to form the first light absorption layer; specifically: Use a customized quartz chamber CSS system, with the temperature of the graphite heater being 580 - 620 °C and the substrate temperature being 380 - 420 °C. Realize gradient doping by segmentally introducing a Cl2 / Ar mixed gas (the proportion of Cl2 is 0.1% - 0.5%), and the deposition rate is 5 - 10 nm / s; low-temperature deposition (<500 °C) can inhibit the lattice distortion of CdTe. Calculated by the Arrhenius equation, the grain boundary diffusion coefficient is reduced by two orders of magnitude, and the defect density is reduced to <10 15 cm -3 .

[0014] Near the FTO side (n + region): Cl2 0.5%, deposit the highly doped layer. The purpose of the high Cl concentration is to passivate interface defects and inhibit interface recombination; Intermediate layer: The Cl2 concentration linearly decreases to 0.1%, deposit the intermediate layer, and the grain boundary density is reduced by >50%; Back contact side (p + region): Introduce AsCl3 vapor (pressure 0.03 - 0.1 Pa), deposit the p + layer. Introduce shallow acceptor levels by As doping to replace Te sites and improve the hole mobility.

[0015] S5. Deposit ZnTe:Cu on the first light absorption layer by magnetron sputtering process, with a deposition thickness of 100 - 200 nm and Cu doping of 2% - 4%; then perform laser annealing at 355 nm (energy density 80 mJ / cm 2 , scanning speed 10 mm / s) to form the back contact layer; Secondary Ion Mass Spectrometry (SIMS) shows that after laser annealing, the Cu diffusion depth <5 nm and the contact resistance is reduced by >30%.

[0016] The above is the structure of the cadmium telluride sub-cell, and a perovskite sub-cell is stacked on the cadmium telluride sub-cell.

[0017] S6. Deposit SnO2:Sb on the back contact layer by magnetron sputtering process, with a deposition thickness of 2 ± 1 nm, Sb doping of 5 at%, and a sputtering power of 150 W to form the second transparent conductive layer. At the same time, the second transparent conductive layer is also the electrode; S7. Deposit CuCrO2:Mg on the second transparent conductive layer by reactive sputtering process with a thickness of 3 ± 1 nm, Mg doping of 3 at%, and O2 flow rate of 10% - 20% to form a hole transport layer, which has strong chemical stability, inhibits the migration of Cu ions in ZnTe:Cu, and promotes the transport of holes from the perovskite to the back electrode; Asymmetric tunneling junction: n + - SnO2:Sb (2 ± 1 nm, carrier concentration 5 × 10 20 cm -3 ) and p + -CuCrO2:Mg (3 ± 1 nm, carrier concentration 8 × 10 19 cm -3 ) form a heterojunction. Based on the Wentzel-Kramers-Brillouin (WKB) approximation calculation, when the conduction band offset ΔEc = 0.15 eV, the tunneling probability T(E) > 92%; The asymmetric tunneling junction realizes the efficient carrier transport between the upper cell (perovskite sub-cell) and the lower cell (CdTe sub-cell). The asymmetric design (n + / p + heterojunction) optimizes the transport paths of electrons and holes respectively, reducing the recombination loss.

[0018] S8. Deposit perovskite Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 (cesium-formamidinium mixed cation lead halide) on the hole transport layer by molecular beam epitaxy (MBE) process, with the substrate temperature of 80 °C, the vacuum degree of 10 -7 Torr, and synchronously inject perfluorodecanoic acid (PFDA) vapor for passivation, with the vapor pressure of 10 -3 Torr and the passivation time of 30 minutes to form the second light absorption layer. The second light absorption layer, as the top cell absorption layer of the tandem cell, broadens the spectral response range.

[0019] In-situ gas phase passivation: Synchronously inject perfluorodecanoic acid (PFDA) vapor during the deposition of perovskite (Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 ), and its -CF2 group bonds with the uncoordinated Pb 2+ bond, and the defect density is reduced to 2 × 10 14 cm -3 (verified by deep level transient spectroscopy (DLTS)).

[0020] On the other hand, the present invention also provides a CdTe-based high-efficiency tandem solar cell structure, formed by the aforementioned preparation method, including a substrate, a cadmium telluride sub-cell prepared on the substrate, and a perovskite sub-cell prepared on the cadmium telluride sub-cell; the structure of the cadmium telluride sub-cell specifically includes: a first transparent conductive layer formed on the substrate, a buffer layer formed on the first transparent conductive layer, a first light absorption layer formed on the buffer layer, and a back contact layer formed on the first light absorption layer; the structure of the perovskite sub-cell specifically includes: a second transparent conductive layer formed on the back contact layer, a hole transport layer formed on the second transparent conductive layer, and a second light absorption layer formed on the hole transport layer.

[0021] Further, the first transparent conductive layer is modified by nitrogen ion implantation. The first light absorption layer is gradient doped with Cl and As along the growth direction.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: By optimizing the energy band of SnO2 through nitrogen ion implantation, improving the carrier lifetime through gradient doping, and alleviating stress through quantum dot superlattice, the single-junction efficiency of the present invention is > 23% and the tandem efficiency is > 31%. The all-dry process is suitable for industrial production on glass substrates and is applicable to high-reliability scenarios. The all-dry process of the present invention does not require solution treatment, avoids the corrosion of perovskite to CdTe, and is compatible with existing production lines. It supports 2200×2600 mm glass substrates with an adjustable light transmittance of 10% - 60%, and is compatible with industrial production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a CdTe-based high-efficiency tandem solar cell structure in an embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram of a cadmium telluride sub-cell structure in an embodiment of the present invention.

[0025] The labels in the figure are: 1, substrate; 2, cadmium telluride sub-cell; 21, first transparent conductive layer; 22, buffer layer; 23, first light absorption layer; 24, back contact layer; 3, perovskite sub-cell; 31, second transparent conductive layer; 32, hole transport layer; 33, second light absorption layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] To fully understand the purpose, features, and effects of the present invention, the present invention will be described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0027] See Figure 1 and Figure 2, the present invention provides a CdTe-based high-efficiency tandem solar cell structure and a preparation method thereof. A cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell. The specific steps are as follows: S1. Provide a substrate and perform pretreatment on the substrate for mechanical support and light transmission.

[0028] S2. Deposit an FTO layer with a thickness of 400 - 550 nm (FTO, fluorine-doped tin oxide) on the substrate by magnetron sputtering. The sheet resistance is 9 - 12 Ω / sq, and the substrate temperature is 400 °C. Then, nitrogen ion implantation is used to optimize the energy band of SnO2 to form a first transparent conductive layer (TCO). The nitrogen ion implantation energy is 50 - 100 keV, and the dose is 1×10 15 ~5×10 16 cm -2 , the vacuum degree is 10 -6 Torr, and the implantation depth is 10 - 30 nm; S3. Grow CdSe on the first transparent conductive layer by close-spaced sublimation to form a buffer layer. During the growth of CdSe, O2 (2% - 5%) is introduced for doping. The substrate temperature is 300 °C, and a CdSe layer with a thickness of 120 - 180 nm is deposited, and its interface recombination velocity < 10 3 cm / s.

[0029] S4. Deposit CdTe on the buffer layer by close-spaced sublimation, and perform gradient doping of Cl (5×10 18 →1×10 17 cm -3 ), As (1×10 17 cm -3 ) to form a first light absorption layer. Specifically: Adopt a customized quartz chamber CSS system. The temperature of the graphite heater is 580 - 620 °C, and the substrate temperature is 380 - 420 °C. By segmentally introducing a Cl2 / Ar mixed gas (the proportion of Cl2 is 0.1% - 0.5%), gradient doping is realized, and the deposition rate is 5 - 10 nm / s. Low-temperature deposition (< 500 °C) can inhibit the lattice distortion of CdTe. Through calculation by the Arrhenius equation, the grain boundary diffusion coefficient is reduced by two orders of magnitude, and the defect density is reduced to < 10 15 cm -3 .

[0030] Near the FTO side (n + region): Cl2 0.5%, deposit a highly doped layer. The purpose of the high Cl concentration is to passivate interface defects and inhibit interface recombination; Intermediate layer: The Cl2 concentration linearly decreases to 0.1%, deposit the intermediate layer, and the grain boundary density is reduced by > 50%; Back contact side (p+ Zone): Introduce AsCl3 vapor (pressure 0.03 - 0.1 Pa) to deposit the p + layer. Introduce shallow acceptor levels by As doping to replace Te sites, improving hole mobility; S5. Deposit ZnTe:Cu on the first light absorption layer by magnetron sputtering, with a deposition thickness of 100 - 200 nm and Cu doping of 2% - 4%; then anneal with a 355 nm laser (energy density 80 mJ / cm 2 , scanning speed 10 mm / s) to form the back contact layer; Secondary Ion Mass Spectrometry (SIMS) shows that the Cu diffusion depth after laser annealing is < 5 nm and the contact resistance is reduced by > 30%.

[0031] S6. Deposit SnO2:Sb on the back contact layer by magnetron sputtering, with a deposition thickness of 2 ± 1 nm, Sb doping of 5 at%, and a sputtering power of 150 W to form the second transparent conductive layer, which is also the electrode; S7. Deposit CuCrO2:Mg on the second transparent conductive layer by reactive sputtering, with a thickness of 3 ± 1 nm, Mg doping of 3 at%, and an O2 flow rate of 10% - 20% to form the hole transport layer, which has strong chemical stability, inhibits the migration of Cu ions in ZnTe:Cu, and promotes the transport of holes from the perovskite to the back electrode; S8. Deposit the perovskite Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 (cesium-formamidinium mixed cation lead halide) on the hole transport layer by Molecular Beam Epitaxy (MBE) process, with a substrate temperature of 80 °C and a vacuum of 10 -7 Torr, and simultaneously inject perfluorodecanoic acid (PFDA) vapor for passivation, with a vapor pressure of 10 -3 Torr and a passivation time of 30 minutes to form the second light absorption layer. Example 1

[0032] S1. The soda-lime glass (3 mm) is ultrasonically cleaned with acetone and isopropanol for 10 minutes each in sequence and dried with nitrogen; S2. Deposit a 500 nm FTO layer (sheet resistance 10 Ω / sq, substrate temperature 400 °C) on the substrate by magnetron sputtering; Use an ion implanter to optimize the energy band of SnO2 by nitrogen ion implantation. The nitrogen ion implantation energy is 80 keV, the dose is 3 × 10 16 cm -2 , the vacuum is 10 -6 Torr, and the implantation depth is 10 - 30 nm; S3. Grow CdSe on the FTO layer, doping with O2 (2% - 5%) during the growth of CdSe, substrate temperature 300 °C, deposit a 180 nm CdSe layer; S4. Deposit CdTe on the CdSe layer, doping with Cl (5×10 18 →1×10 17 cm -3 ), As (1×10 17 cm -3 ) along the growth direction in a gradient manner; specifically: Adopt a customized quartz chamber CSS system, graphite heater temperature 580 - 620 °C, substrate temperature 380 - 420 °C. Inject a Cl2 / Ar mixed gas in segments: 0 - 10 minutes: Cl2 0.5%, deposit a 1 μm highly doped layer; 10 - 25 minutes: Cl2 linearly decreases to 0.1%, deposit a 1.5 μm transition layer; 25 - 30 minutes: Inject AsCl3 vapor (pressure 0.05 Pa), deposit a 0.5 μm p + layer.

[0033] S5. Magnetron sputter ZnTe:Cu (200 nm, Cu doping 2%) on the CdSe layer; then anneal with a 355 nm laser (energy density 80 mJ / cm 2 , scanning speed 10 mm / s) to form a back contact layer; S6. Magnetron sputter SnO2:Sb (2 nm, Sb doping 5 at%) on the ZnTe:Cu layer, sputtering power 150 W; S7. Reactively sputter CuCrO2:Mg (3 nm, Mg doping 3 at%) on the ZnTe:Cu layer, O2 flow rate 10% to form a hole transport layer; S8. Deposit Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 by molecular beam epitaxy (MBE), substrate temperature 80 °C, vacuum degree 10 -7 Torr, synchronously inject perfluorodecanoic acid (PFDA) vapor for passivation, vapor pressure 10 -3 Torr, passivation time 30 minutes.

[0034] Perform performance and reliability tests on the battery prepared in Example 1: (I) Single - junction CdTe battery: Efficiency breakthrough: Laboratory tests (under AM1.5G standard illumination) show that Voc = 1,017 mV, Jsc = 28.5 mA / cm 2, FF = 79%, η = 22.9%; Stability: After 1000 hours of damp heat aging at 85°C / 85%RH, the efficiency decay < 0.8% / kh, and electroluminescence (EL) imaging shows no microcracks.

[0035] (II) CdTe / perovskite tandem cell: Tandem cell efficiency: PCE = 31.6% (Voc = 2.05V, Jsc = 18.9mA / cm 2 , FF = 82.3%); Damp heat aging (85°C / 85%RH, 1000h): The efficiency decay rate is 0.75% / kh, and EL imaging shows no microcracks.

[0036] Reliability: Passed the IEC 61215:2021 enhanced test (double 85 conditions for 1500 hours), and the yellowness index ΔYI < 1.5.

[0037] Finally, it should be noted that the above - listed are only the preferred embodiments of the present invention. Of course, those skilled in the art can make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and its equivalent technologies, they should be considered as within the protection scope of the present invention.

Claims

1. A preparation method of a CdTe-based high-efficiency tandem solar cell, characterized in that, A cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell. The specific steps are as follows: S1. Provide a substrate and perform pretreatment on the substrate; S2. Deposit an FTO layer on the substrate by magnetron sputtering, and then optimize the energy band of SnO2 by nitrogen ion implantation to form a first transparent conductive layer; S3. Grow CdSe on the first transparent conductive layer by close-spaced sublimation to form a buffer layer; S4. Deposit CdTe on the buffer layer by close-spaced sublimation, and gradient-dope Cl and As along the growth direction to form a first light absorption layer; S5. Deposit ZnTe:Cu on the first light absorption layer by magnetron sputtering and perform laser annealing treatment to form a back contact layer; S6. Deposit SnO2:Sb on the back contact layer by magnetron sputtering to form a second transparent conductive layer; S7. Deposit CuCrO2:Mg on the second transparent conductive layer by reactive sputtering to form a hole transport layer; S8. Deposit perovskite on the hole transport layer by molecular beam epitaxy and synchronously inject PFDA vapor for passivation to form a second light absorption layer.

2. The preparation method of the CdTe-based high-efficiency tandem solar cell according to claim 1, wherein In step S2, the nitrogen ion implantation energy is 50 - 100 keV, and the dose is 1×10 15 ~5×10 16 cm -2 , and the implantation depth is 10 - 30 nm.

3. The preparation method of the CdTe-based high-efficiency tandem solar cell according to claim 1, characterized in that, In step S3, during the process of growing CdSe by close-spaced sublimation, O2 is doped, and the O2 flow rate is 2% - 5%.

4. The preparation method of the CdTe-based high-efficiency tandem solar cell according to claim 1, characterized in that In step S4, Cl is doped with a gradient along the growth direction: 5×10 18 →1×10 17 cm -3 , and As is doped with a gradient along the growth direction: 1×10 17 cm -3 ; specifically: The Cl2 / Ar mixed gas is introduced in segments: Near the FTO side: Deposit a highly doped layer, and the high Cl concentration inhibits interface recombination; Intermediate layer: The Cl2 concentration decreases linearly, deposit the intermediate layer, and the grain boundary density decreases by >50%; Back contact side: Introduce AsCl3 vapor, and As doping improves the hole mobility.

5. The preparation method of the CdTe-based high-efficiency tandem solar cell according to claim 1, characterized in that, In step S8, the perovskite is Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 .

6. The preparation method of the CdTe-based high-efficiency tandem solar cell according to claim 1, wherein, The substrate is soda-lime glass with a thickness of 3 mm; the thickness of the first transparent conductive layer is 400 - 550 nm, and the sheet resistance is 9 - 12 Ω / sq; the thickness of the buffer layer is 120 - 180 nm; the thickness of the first light absorption layer is 2 - 4 μm; the thickness of the back contact layer is 100 - 200 nm, and the Cu doping is 2% - 4%; the thickness of the second transparent conductive layer is 2 ± 1 nm, and the Sb doping is 5 at%; the thickness of the hole transport layer is 3 ± 1 nm, and the Mg doping is 3 at%.

7. A CdTe-based high-efficiency tandem solar cell structure, characterized in that, Formed by the preparation method according to any one of claims 1 - 6, including a substrate, a cadmium telluride sub-cell is prepared on the substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell; The structure of the cadmium telluride sub-cell specifically includes: a first transparent conductive layer is formed on the substrate, a buffer layer is formed on the first transparent conductive layer, a first light absorption layer is formed on the buffer layer, and a back contact layer is formed on the first light absorption layer; the structure of the perovskite sub-cell specifically includes: a second transparent conductive layer is formed on the back contact layer, a hole transport layer is formed on the second transparent conductive layer, and a second light absorption layer is formed on the hole transport layer.

8. The CdTe-based high-efficiency tandem solar cell structure according to claim 7, characterized in that, The first transparent conductive layer is modified by nitrogen ion implantation.

9. The CdTe-based high-efficiency tandem solar cell structure according to claim 7, wherein, The first light absorption layer is gradient-doped with Cl and As along the growth direction.

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