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

Abstract

The present invention relates to the field of solar cell technology, and discloses a CdTe-based high-efficiency stacked solar cell structure and a preparation method thereof. The cell structure includes a substrate, a first transparent conductive layer is formed on the substrate, a buffer layer is formed on the first transparent conductive layer, a first light absorbing layer is formed on the buffer layer, and a back contact layer is formed on the first light absorbing layer to obtain a cadmium telluride sub-cell; 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 absorbing layer is formed on the hole transport layer to obtain a perovskite sub-cell. The TCO layer of the present application optimizes the SnO2 energy band through nitrogen ion implantation, and the first light absorbing layer is gradiently doped with Cl and As to improve the carrier lifetime, thereby achieving a single junction efficiency of >23% and a stacking efficiency of >31%. The fully dry process of the present invention is suitable for the industrial production of glass substrates and is applicable to high-reliability scenarios.

Description

Technical Field

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

[0002] Thin-film solar cells are a new type of photovoltaic device that can alleviate the energy crisis. They can be manufactured using a variety of inexpensive substrates, including ceramics, graphite, and metal sheets. Amidst the ongoing 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, also known as CdTe cells, are compound semiconductor thin-film solar cells with CdTe as the light-absorbing layer. They have a bandgap of 1.2 to 1.3 eV and a high absorption coefficient in the visible light wavelength range (600 nm to 1000 nm), resulting in high conversion efficiency and low cost. Pure inorganic perovskite thin-film solar cells use organic metal halide semiconductors as the absorption layer. They also have a bandgap of 1.6 to 1.7 eV and a high absorption coefficient in the short-wavelength range (250 nm to 700 nm).

[0003] Traditional solar thin-film cells are generally single-layer. In the past few years, many manufacturers have used stacking technology to prepare amorphous silicon thin-film cells. However, amorphous silicon thin-film cells have serious SW effects that cannot be fundamentally solved. Traditional single-layer thin-film cells such as cadmium telluride, copper indium gallium selenide, gallium arsenide, and perovskite have slow efficiency improvements in the process of large-scale preparation and face some major problems: (1) The conduction band offset problem of the SnO2 buffer layer of CdTe cells: There is a negative offset of 0.3 eV between the conduction band bottom of the unmodified SnO2 (~4.2 eV) and the conduction band bottom of the CdSeTe absorption layer (~4.5 eV), which leads to the accumulation of interface electrons and a recombination rate of 1×10 4 cm / s (verified by TRPL test), limiting the Voc improvement, Voc < 900 mV; (2) CdTe material defects: Te vacancies (V_Te) and Cd interstitials (Cd_i) form deep energy level recombination centers, and the carrier lifetime is < 10 ns (calculated by the quasi-Fermi level splitting model); (3) High temperature process defects: Traditional close space sublimation (CSS) deposition requires 500-600 °C, inducing Te vacancy concentration in the CdTe lattice to be > 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 exacerbates 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°C, 20 min) to passivate grain boundaries, but this fails to address the band offset issue, limiting Voc 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] To address these technical issues, the present invention provides a CdTe-based high-efficiency tandem solar cell structure and its fabrication method. By optimizing the SnO2 energy band through nitrogen ion implantation, increasing carrier lifetime through gradient doping, and alleviating stress through quantum dot superlattices, the structure achieves single-junction efficiencies exceeding 23% and tandem efficiencies exceeding 31%. This fully dry process is suitable for industrialized glass substrate production and is ideal for high-reliability scenarios.

[0006] To achieve this technical purpose, the present invention adopts the following scheme:

[0007] A method for preparing a CdTe-based high-efficiency tandem solar cell, wherein a cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell, specifically comprising the following steps:

[0008] S1. Provide a substrate and pre-treat the substrate;

[0009] S2, depositing an FTO layer on the substrate using a magnetron sputtering process, followed by nitrogen ion implantation to optimize the SnO2 energy band to form the first transparent conductive layer (TCO);

[0010] S3, growing CdSe on the first transparent conductive layer using a close space sublimation method (CSS) to form a buffer layer;

[0011] S4, depositing CdTe on the buffer layer by a close-space sublimation method, and gradient-doping Cl and As along the growth direction to form a first light absorption layer;

[0012] S5, depositing ZnTe:Cu on the first light absorbing layer by a magnetron sputtering process, and performing laser annealing to form a back contact layer;

[0013] S6, depositing SnO2:Sb on the back contact layer by a magnetron sputtering process to form a second transparent conductive layer;

[0014] S7, depositing CuCrO2:Mg on the second transparent conductive layer by a reactive sputtering process to form a hole transport layer;

[0015] S8. Depositing perovskite on the hole transport layer using a molecular beam epitaxy process, and simultaneously injecting PFDA vapor for passivation to form a second light absorption layer.

[0016] Furthermore, the preferred embodiment of the present invention is:

[0017] A method for preparing a CdTe-based high-efficiency tandem solar cell, wherein a cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell, specifically comprising the following steps:

[0018] S1. Provide a substrate and pre-treat the substrate for mechanical support and light transmission. In this application, the substrate is soda-lime glass (3 mm). Ultrasonic cleaning is performed in acetone and isopropyl alcohol for 10 minutes each, followed by drying with nitrogen and set aside.

[0019] S2. Deposit a 400-550 nm FTO layer (FTO, fluorine-doped tin oxide) on the substrate using magnetron sputtering with a sheet resistance of 9-12 Ω / sq at a substrate temperature of 400°C. Then, nitrogen ion implantation is performed to optimize the SnO2 energy band to form the 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 , vacuum degree 10 -6 Torr, the injection depth is 10~30 nm.

[0020] X-ray photoelectron spectroscopy (XPS) analysis showed that the work function of SnO2 after nitrogen ion implantation was increased to 5.075 eV, and the interface recombination rate was reduced to 5×10 3 cm / s; the theoretical basis is: density functional theory (DFT) calculations show that N doping introduces oxygen vacancy compensation, the conduction band edge shifts down by 0.15 eV, and the energy band matching is optimized.

[0021] The first transparent conductive layer (TCO) serves as the battery's electrode to collect current, and nitrogen ion implantation optimizes the energy band matching with CdTe.

[0022] S3. CdSe is grown on the first transparent conductive layer by close-space sublimation to form a buffer layer. O2 (2% to 5%) is introduced into the process of growing CdSe. The substrate temperature is 300°C. A 120-180 nm CdSe layer is deposited. The interface recombination velocity is less than 10 3 cm / s.

[0023] The buffer layer can reduce the lattice mismatch between CdTe and TCO interface, and O doping can passivate the surface state and reduce the interface recombination rate.

[0024] S4, CdTe was deposited on the buffer layer by close space sublimation method, and Cl was gradient doped along the growth direction (5×10 18 →1×10 17 cm -3 )、As(1×10 17 cm -3 ), forming a first light absorbing layer; specifically:

[0025] A custom quartz chamber CSS system was used, with a graphite heater temperature of 580-620°C and a substrate temperature of 380-420°C. Gradient doping was achieved by introducing a Cl2 / Ar gas mixture (Cl2 content 0.1%-0.5%) in stages, with a deposition rate of 5-10 nm / s. Low-temperature deposition (<500°C) suppressed CdTe lattice distortion, and the grain boundary diffusion coefficient was reduced by two orders of magnitude, according to the Arrhenius equation, reducing the defect density to <10 15 cm -3 .

[0026] Near FTO side (n + Area): Cl2 0.5%, depositing highly doped layers. The purpose of high Cl concentration is to passivate interface defects and inhibit interface recombination;

[0027] Intermediate layer: Cl2 concentration decreases linearly to 0.1%, depositing the intermediate layer, and the grain boundary density decreases by >50%;

[0028] Back contact side (p + Zone): AsCl3 vapor (pressure 0.03~0.1Pa) is introduced to deposit p + layer, and shallow acceptor energy levels are introduced by replacing Te sites with As doping to improve hole mobility.

[0029] S5. Deposit ZnTe:Cu on the first light absorbing layer by magnetron sputtering, with a deposition thickness of 100-200 nm and Cu doping of 2%-4%. Then, anneal with 355 nm laser (energy density 80 mJ / cm 2, scanning speed 10mm / s), forming a back contact layer; secondary ion mass spectrometry (SIMS) showed that after laser annealing, the Cu diffusion depth was less than 5nm and the contact resistance was reduced by more than 30%.

[0030] The above is the structure of the cadmium telluride sub-cell, with the perovskite sub-cell superimposed on the cadmium telluride sub-cell.

[0031] S6. Depositing SnO2:Sb on the back contact layer by magnetron sputtering with a deposition thickness of 2±1 nm, Sb doping 5 at%, and sputtering power of 150 W to form a second transparent conductive layer, which also serves as an electrode;

[0032] S7. CuCrO2:Mg is deposited on the second transparent conductive layer by a reactive sputtering process with a thickness of 3±1 nm, Mg doping of 3 at%, and an O2 flow rate of 10%~20% to form a hole transport layer with strong chemical stability, which inhibits the migration of Cu ions in ZnTe:Cu and promotes the transport of holes from the perovskite to the back electrode;

[0033] Asymmetric tunneling junction: n + - SnO2:Sb(2±1nm, carrier concentration 5×10 20 cm -3 ) and p + -CuCrO2:Mg(3±1nm,carrier concentration 8×10 19 cm -3 ) forms a heterojunction. Based on the Wentzel-Kramers-Brillouin (WKB) approximation, when the conduction band offset ΔEc = 0.15 eV, the tunneling probability T(E) is greater than 92%;

[0034] Asymmetric tunneling junction enables efficient carrier transfer between the upper cell (perovskite subcell) and the lower cell (CdTe subcell). + / p + Heterojunction) optimizes the transmission paths of electrons and holes respectively, reducing recombination losses.

[0035] S8, using molecular beam epitaxy (MBE) to deposit perovskite Cs on the hole transport layer 0.15 FA 0.85 PbI 2.5 Br 0.5 (cesium-formamidine mixed cation lead halide), substrate temperature 80 ° C, vacuum degree 10 -7 Torr, simultaneous injection of perfluorodecanoic acid (PFDA) vapor passivation, vapor pressure 10 -3 Torr, passivation time 30 minutes, forming 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.

[0036] In situ gas phase passivation: In perovskite (Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 ) During the deposition process, perfluorodecanoic acid (PFDA) vapor is injected simultaneously, and its -CF2 group reacts with the uncoordinated Pb 2+ bonding, the defect density is reduced to 2×10 14 cm -3 (Deep Level Transient Spectroscopy (DLTS) verification).

[0037] On the other hand, the present invention also provides a CdTe-based high-efficiency stacked solar cell structure, which is formed using 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: forming a first transparent conductive layer on the substrate, forming a buffer layer on the first transparent conductive layer, forming a first light absorption layer on the buffer layer, and forming a back contact layer on the first light absorption layer; the structure of the perovskite sub-cell specifically includes: 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.

[0038] Furthermore, the first transparent conductive layer is modified by nitrogen ion implantation. The first light absorbing layer is gradiently doped with Cl and As along the growth direction.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention achieves single-junction efficiencies exceeding 23% and stacking efficiencies exceeding 31% through nitrogen ion implantation to optimize SnO2 bandgap energy, gradient doping to enhance carrier lifetime, and stress relief using quantum dot superlattices. The fully dry process is suitable for industrial glass substrate production and is ideal for high-reliability scenarios. This fully dry process eliminates the need for solution treatment, preventing perovskite corrosion on CdTe and making it compatible with existing production lines. It supports glass substrates up to 2200×2600 mm, with an adjustable transmittance from 10% to 60%, making it suitable for industrial production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of a CdTe-based high-efficiency tandem solar cell in an embodiment of the present invention.

[0042] Figure 2 Schematic diagram of the structure of a cadmium telluride sub-battery in an embodiment of the present invention.

[0043] Marked 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

[0044] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0045] See also Figure 1 and Figure 2 The present invention provides a CdTe-based high-efficiency tandem solar cell structure and a preparation method thereof, wherein a cadmium telluride sub-cell is prepared on a substrate, and a perovskite sub-cell is prepared on the cadmium telluride sub-cell, specifically comprising the following steps:

[0046] S1. Provide a substrate and pre-treat the substrate for mechanical support and light transmission.

[0047] S2. Deposit a 400-550 nm FTO layer (FTO, fluorine-doped tin oxide) on the substrate using a magnetron sputtering process with a sheet resistance of 9-12 Ω / sq at a substrate temperature of 400°C. Then, nitrogen ion implantation is performed to optimize the SnO2 energy band to form the 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 , vacuum degree 10 -6 Torr, injection depth is 10~30 nm;

[0048] S3. CdSe is grown on the first transparent conductive layer by close-space sublimation to form a buffer layer. O2 (2% to 5%) is introduced into the process of growing CdSe. The substrate temperature is 300°C. A 120-180 nm CdSe layer is deposited. The interface recombination velocity is less than 10 3 cm / s.

[0049] S4, CdTe was deposited on the buffer layer by close space sublimation method, and Cl was gradient doped along the growth direction (5×10 18 →1×10 17 cm -3 )、As(1×10 17 cm -3 ), forming a first light absorbing layer; specifically:

[0050] A custom quartz chamber CSS system was used, with a graphite heater temperature of 580-620°C and a substrate temperature of 380-420°C. Gradient doping was achieved by introducing a Cl2 / Ar gas mixture (Cl2 content 0.1%-0.5%) in stages, with a deposition rate of 5-10 nm / s. Low-temperature deposition (<500°C) suppressed CdTe lattice distortion, and the grain boundary diffusion coefficient was reduced by two orders of magnitude, according to the Arrhenius equation, reducing the defect density to <10 15 cm -3 .

[0051] Near FTO side (n + Area): Cl2 0.5%, depositing highly doped layers. The purpose of high Cl concentration is to passivate interface defects and inhibit interface recombination;

[0052] Intermediate layer: Cl2 concentration decreases linearly to 0.1%, depositing the intermediate layer, and the grain boundary density decreases by >50%;

[0053] Back contact side (p + Zone): AsCl3 vapor (pressure 0.03~0.1Pa) is introduced to deposit p + layer, by replacing Te sites with As doping to introduce shallow acceptor energy levels and improve hole mobility;

[0054] S5. Deposit ZnTe:Cu on the first light absorbing layer by magnetron sputtering, with a deposition thickness of 100-200 nm and Cu doping of 2%-4%. Then, anneal with 355 nm laser (energy density 80 mJ / cm 2 , scanning speed 10mm / s), forming a back contact layer; secondary ion mass spectrometry (SIMS) showed that after laser annealing, the Cu diffusion depth was less than 5nm and the contact resistance was reduced by more than 30%.

[0055] S6. Depositing SnO2:Sb on the back contact layer by magnetron sputtering with a deposition thickness of 2±1 nm, Sb doping 5 at%, and sputtering power of 150 W to form a second transparent conductive layer, which also serves as an electrode;

[0056] S7. CuCrO2:Mg is deposited on the second transparent conductive layer by a reactive sputtering process with a thickness of 3±1 nm, Mg doping of 3 at%, and an O2 flow rate of 10%~20% to form a hole transport layer with strong chemical stability, which inhibits the migration of Cu ions in ZnTe:Cu and promotes the transport of holes from the perovskite to the back electrode;

[0057] S8, using molecular beam epitaxy (MBE) to deposit perovskite Cs on the hole transport layer 0.15 FA 0.85 PbI 2.5 Br 0.5(cesium-formamidine mixed cation lead halide), substrate temperature 80 ° C, vacuum degree 10 -7 Torr, simultaneous injection of perfluorodecanoic acid (PFDA) vapor passivation, vapor pressure 10 -3 Torr, the passivation time is 30 minutes, and the second light absorption layer is formed. Example 1

[0058] S1, soda-lime glass (3 mm) was ultrasonically cleaned with acetone and isopropanol for 10 min each, and dried with nitrogen;

[0059] S2, depositing a 500 nm FTO layer on the substrate by magnetron sputtering (square resistance 10 Ω / sq, substrate temperature 400°C);

[0060] Using an ion implanter, nitrogen ions were implanted to optimize the SnO2 energy band. The nitrogen ion implantation energy was 80 keV and the dose was 3×10 16 cm -2 , vacuum degree 10 -6 Torr, injection depth is 10~30 nm;

[0061] S3, growing CdSe on the FTO layer by CSS, doping with O2 (2%-5%) during the growth of CdSe, with the substrate temperature at 300°C, and depositing a 180nm CdSe layer;

[0062] S4, CSS deposited CdTe on the CdSe layer, and doped Cl (5×10 18 →1×10 17 cm -3 )、As(1×10 17 cm -3 ); specifically:

[0063] A custom quartz chamber CSS system was used, with a graphite heater temperature of 580-620°C and a substrate temperature of 380-420°C. Cl2 / Ar mixed gas was introduced in stages:

[0064] 0-10 minutes: Cl2 0.5%, depositing a 1μm highly doped layer;

[0065] 10-25 minutes: Cl2 is linearly reduced to 0.1%, and a 1.5 μm transition layer is deposited;

[0066] 25~30 minutes: AsCl3 vapor (pressure 0.05Pa) is introduced to deposit 0.5μm p + layer.

[0067] S5, magnetron sputtering ZnTe:Cu (200nm, Cu doping 2%) on the CdSe layer; then annealing with 355nm laser (energy density 80mJ / cm2 , scanning speed 10 mm / s), forming a back contact layer;

[0068] S6, magnetron sputtering SnO2:Sb (2nm, Sb doping 5at%) on the ZnTe:Cu layer, sputtering power 150W;

[0069] S7, CuCrO2:Mg (3 nm, Mg doping 3 at%) was reactively sputtered on the ZnTe:Cu layer with an O2 flow rate of 10% to form a hole transport layer;

[0070] S8, Cs deposition by molecular beam epitaxy (MBE) 0.15 FA 0.85 PbI 2.5 Br 0.5 , substrate temperature is 80℃, vacuum degree is 10 -7 Torr, simultaneous injection of perfluorodecanoic acid (PFDA) vapor passivation, vapor pressure 10 -3 Torr, passivation time 30 minutes.

[0071] The performance and reliability tests of the battery prepared in Example 1 were carried out:

[0072] (1) Single-junction CdTe cell:

[0073] Efficiency breakthrough: Laboratory tests (AM1.5G standard light) show Voc=1,017 mV, Jsc=28.5 mA / cm 2 , FF=79%,η=22.9%;

[0074] Stability: After 1000 hours of damp heat aging at 85°C / 85%RH, efficiency degradation is less than 0.8% / kh, and electroluminescence (EL) imaging shows no microcracks.

[0075] (2) CdTe / perovskite tandem cells:

[0076] Tandem cell efficiency: PCE=31.6% (Voc=2.05V, Jsc=18.9mA / cm 2 , FF=82.3%));

[0077] Damp-heat aging (85°C / 85%RH, 1000h): efficiency decay rate 0.75% / kh, EL imaging shows no microcracks.

[0078] Reliability: Passed the IEC 61215:2021 strict test (double 85 conditions for 1500 hours), yellowing index ΔYI < 1.5.

[0079] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art may 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 their equivalents, they should be considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a CdTe-based high-efficiency tandem solar cell, characterized in that: A cadmium telluride subcell is prepared on a substrate, and a perovskite subcell is prepared on the cadmium telluride subcell, specifically comprising the following steps: S1. Provide a substrate and pre-treat the substrate; S2, depositing an FTO layer on the substrate using a magnetron sputtering process, and then implanting nitrogen ions to optimize the SnO2 energy band to form a first transparent conductive layer; S3, growing CdSe on the first transparent conductive layer by a close-space sublimation method to form a buffer layer; S4, CdTe was deposited on the buffer layer by close space sublimation method, and Cl was gradient doped along the growth direction: 5×10 18 →1×10 17 cm -3 、As:1×10 17 cm -3 , forming a first light absorbing layer; S5, depositing ZnTe:Cu on the first light absorbing layer by a magnetron sputtering process, and performing laser annealing to form a back contact layer; S6, depositing SnO2:Sb on the back contact layer by a magnetron sputtering process to form a second transparent conductive layer; S7, depositing CuCrO2:Mg on the second transparent conductive layer by a reactive sputtering process to form a hole transport layer; S8. Depositing perovskite on the hole transport layer using a molecular beam epitaxy process, and simultaneously injecting PFDA vapor for passivation to form a second light absorption layer.

2. The method for preparing a 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 , the injection depth is 10~30 nm.

3. The method for preparing a CdTe-based high-efficiency tandem solar cell according to claim 1, wherein: In step S3, O2 is introduced into the process of growing CdSe by close-space sublimation method, and the amount of O2 introduced is 2% to 5%.

4. The method for preparing a CdTe-based high-efficiency tandem solar cell according to claim 1, wherein: The specific operation of gradient doping of Cl and As along the growth direction in step S4 is as follows: Introduce Cl2 / Ar mixed gas in stages: Near the FTO side: Deposit a highly doped layer, and the high Cl concentration inhibits interface recombination; Intermediate layer: Cl2 concentration decreases linearly, depositing the intermediate layer, and the grain boundary density decreases by more than 50%; Back contact side: AsCl3 vapor is introduced, and As doping improves hole mobility.

5. The method for preparing a CdTe-based high-efficiency tandem solar cell according to claim 1, wherein: In step S8, the perovskite is Cs 0.15 FA 0.85 PbI 2.5 Br 0.5 .

6. The method for preparing a 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 first transparent conductive layer has a thickness of 400~550 nm and a square resistance of 9~12 Ω / sq; the buffer layer has a thickness of 120~180 nm; the first light absorption layer has a thickness of 2~4 μm; the back contact layer has a thickness of 100~200 nm and is doped with Cu 2%~4%; the second transparent conductive layer has a thickness of 2±1 nm and is doped with Sb 5at%; the hole transport layer has a thickness of 3±1 nm and is doped with Mg 3at%.

7. A CdTe-based high-efficiency tandem solar cell structure, characterized in that: The method according to any one of claims 1 to 6 is used to form the battery, comprising 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: forming a first transparent conductive layer on a substrate, forming a buffer layer on the first transparent conductive layer, forming a first light absorbing layer on the buffer layer, and forming a back contact layer on the first light absorbing layer; the structure of the perovskite sub-cell specifically includes: 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 absorbing layer 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, characterized in that: The first light absorbing layer is gradiently doped with Cl and As along the growth direction.

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