A silicon-based tandem solar cell and its manufacturing method

Abstract

The present invention discloses a silicon-based tandem solar cell, which comprises a bottom cell structure and a top cell structure stacked on the bottom cell structure. The bottom cell structure includes an n-type monocrystalline silicon substrate, with a SiO2 insulating layer disposed around the upper surface of the n-type monocrystalline silicon substrate, a p-type doped layer is prepared in the middle, and a periodic array structure of vertical nanopores is etched and prepared in the stacked area of the p-type doped layer and the n-type monocrystalline silicon substrate. The nanopores in the n-type monocrystalline silicon substrate are voids, and a metal thin film layer is disposed on the lower surface of the n-type monocrystalline silicon substrate; the top cell structure sequentially includes a TiO2 thin film layer, a perovskite absorption layer, a hole transport layer, a transparent conductive thin film layer, and a metal electrode from bottom to top. The present invention utilizes the excellent light absorption and charge transport properties of the periodic nanopore array to improve the utilization efficiency of long-wavelength photons of the bottom cell, and improves the photoelectric conversion efficiency of the tandem solar cell while being compatible with the silicon-based cell process.

Description

Technical Field

[0001] The present invention relates to a solar cell and a preparation method thereof, and particularly to a silicon-based tandem solar cell and a preparation method thereof. Background Art

[0002] Solar energy is a renewable clean energy and is of great significance for the sustainable development of mankind. A solar cell directly converts light energy into electrical energy, and the photoelectric conversion efficiency and preparation cost are the key factors determining its industrial application. At present, silicon-based solar cells are the mainstream of solar cells, occupying 90% of the global photovoltaic market. The efficiency of silicon-based solar cells has reached 25.6%, approaching the Shockley-Queisser limit efficiency (29.4%), but the preparation cost remains high. The development of silicon-based solar cells requires reducing the preparation cost and at the same time improving the efficiency of the cells.

[0003] Since the energy distribution of the solar spectrum is relatively wide, for any semiconductor material, only photons with energy values greater than its band gap can be absorbed. Therefore, a tandem cell is formed by stacking a wide-bandgap light absorption material on the top layer of a silicon cell. While taking into account the mature process of silicon cells, the cell efficiency can be improved [M.A. Green. Prog. Photovoltaics 2018, 26, 427]. At present, the theoretical limit efficiency of the reported silicon-based tandem cells can be increased from 29% to 42.5%.

[0004] Perovskite solar cells use CH 3 NH 3 PbX 3 (X = I, C, Br) as a photoelectric conversion material. Its performance has been significantly improved in just a few years. From the photoelectric conversion efficiency of 3.8% in 2009, the efficiency can reach as high as 22.1% so far. Perovskite materials are also considered to be the most promising next-generation low-cost solar cell light absorption materials. When the band gap of perovskite is 1.55 eV, it can absorb photons with wavelengths less than 800 nm, while crystalline silicon with a band gap of 1.12 eV can absorb photons with wavelengths greater than 800 nm in the solar spectrum. When the two are formed into a tandem cell from top to bottom, their absorption spectra are complementary, greatly improving the utilization rate of the solar spectrum and at the same time reducing the preparation cost. The perovskite / crystalline silicon tandem solar cell developed by The Hong Kong Polytechnic University not only reduces the cost by 30.6% compared with silicon-based cells, but also has an efficiency of 25.5%.

[0005] The Chinese patent with the publication number CN109935690A prepared a tunnel junction and a perovskite absorption layer at low temperature. The efficiency of the silicon heterojunction / perovskite two-electrode stacked solar cell prepared by a simple and low-cost solution method can ultimately reach 22.22%. The Chinese patent with the publication number CN209709024U designed a double-sided light-receiving perovskite / p-type crystalline silicon substrate stacked solar cell, enabling the back surface of the crystalline silicon solar cell serving as the substrate to absorb additional scattered light, which has a certain improvement on the overall performance of the stacked device.

[0006] Although the performance of existing perovskite / crystalline silicon stacked cells has been significantly improved, it still cannot meet the requirements of industrialization. Therefore, it is very necessary to explore a better light absorption structure to improve the light absorption of the device, and then prepare high-performance battery devices. Summary of the Invention

[0007] An object of the present invention is to provide a silicon-based stacked solar cell, which solves the problem of low absorption efficiency of long-wavelength photons in the stacked cell by utilizing the excellent light trapping ability of the silicon pore array. At the same time, the silicon pore array can be prepared by a metal-assisted chemical process at room temperature, which improves the photon absorption efficiency without increasing the preparation cost. Another object of the present invention is to provide a preparation method for such a silicon-based stacked solar cell.

[0008] The technical solution of the present invention is as follows: A silicon-based stacked solar cell includes a bottom cell structure and a top cell structure. The top cell structure is stacked on the bottom cell structure. The bottom cell structure includes an n-type monocrystalline silicon substrate, and SiO 2 insulating layers are provided around the upper surface of the n-type monocrystalline silicon substrate to form a light-receiving window in the central region of the n-type monocrystalline silicon substrate. A p-type doping layer is prepared on the n-type monocrystalline silicon substrate in the light-receiving window region. A vertical nanohole periodic array structure is etched in the stacked region of the p-type doping layer and the n-type monocrystalline silicon substrate. The nanoholes in the n-type monocrystalline silicon substrate are voids, and a metal thin film layer is provided on the lower surface of the n-type monocrystalline silicon substrate. The top cell structure sequentially includes TiO 2 thin film layer, perovskite absorption layer, hole transport layer, transparent conductive thin film layer and metal electrode from bottom to top. The metal electrode and the metal thin film layer are respectively led out as conductive electrodes to supply power to the external circuit.

[0009] Preferably, the period of the nanohole periodic array structure is 600-1200 nm, the diameter of the nanoholes of the nanohole periodic array structure is 400-600 nm, the depth is 400-800 nm, and the duty cycle of the nanohole periodic array structure is 1 / 3-2 / 3.

[0010] Preferably, the TiO 2The thickness of the film is 50 to 300 nm.

[0011] Preferably, the thickness of the perovskite absorption layer is 100-500 nm.

[0012] Preferably, the hole transport layer is one of nickel oxide, tungsten oxide and Spiro-OMeTAD, and has a thickness of 150 to 800 nm.

[0013] Preferably, the material of the metal electrode is one of Au, Ag, Al, Gu and Pt, and the thickness is 10 to 500 nm.

[0014] A method for preparing a silicon-based laminated solar cell, characterized in that it comprises the following steps: 1. depositing a layer of SiO2 on the n-type single crystal silicon substrate; 2 The insulating layer forms a light receiving window; second, a PN junction is prepared on the surface of the n-type single crystal silicon substrate in the light receiving window region by high temperature diffusion of a liquid boron source; third, a vertical nanopore periodic array structure is prepared on the PN junction by a metal-assisted chemical etching method; fourth, a TiO 2 The thin film layer is used as an electron transport layer; Fifth, annealing and curing are performed and the TiO 2 A perovskite absorption layer and a hole transport layer are sequentially prepared on the thin film layer by a spin coating method; Sixth, a transparent conductive thin film layer and a metal electrode are separately prepared on the surface of the hole transport layer by an electron beam evaporation process; Seventh, a metal thin film layer lead-out wire is deposited on the lower surface of the n-type single crystal silicon substrate as the negative electrode of the silicon-based stacked solar cell, and the metal electrode lead-out wire is used as the positive electrode of the silicon-based stacked solar cell.

[0015] Preferably, in the process of preparing the vertical nanopore periodic array structure by metal-assisted chemical method, a silver nano-colloid is spin-coated on a silicon wafer for preparing a PN junction by using a coating machine, the rotation speed is 2500-5000r / min, and the diameter of the silver nano-particles is 50-800nm; after spin coating, it is immersed in a hydrogen peroxide solution for etching, the concentration of the solution is 0.2-2mol / L, and the time is 0.5-2h; after the nanopore periodic array is formed, the silver nano-particles are removed by a nitric acid solution.

[0016] Preferably, the resistivity of the n-type single crystal silicon substrate is 1.2-1.3 Ω·cm, and the concentration of the boron source is 15-16 mg / cm when the PN junction is prepared by high temperature diffusion of the liquid boron source. 3 BBr 3 The liquid boron source is diffused at a high temperature of 1200-1250° C. to prepare a p-type doped layer.

[0017] Preferably, the spin coating method is used to prepare TiO 2When forming the thin film layer, a spin-coating solution is prepared using titanium isopropoxide as the titanium source and spin-coated at a speed of 2000 - 3500 r / min. During annealing and curing, the annealing temperature is 380 - 650 °C and the annealing time is 1 - 3 h. The thickness of the 2 TiO thin film layer is 10 - 300 nm.

[0018] The advantages of the technical solution provided by the present invention are as follows: The silicon nanopore array with better light trapping characteristics is used as the bottom cell structure of the perovskite / silicon tandem solar cell. Compared with the planar silicon structure, it has better light absorption performance; compared with the existing textured light trapping structure technology, the surface of the silicon nanopore array is flatter and the mechanical properties are more stable. Thanks to the excellent light absorption and charge transport properties of the periodic nanopore array, the utilization efficiency of long-wavelength photons of the bottom cell is greatly improved, and the photoelectric conversion efficiency of the tandem solar cell is increased while being compatible with the silicon-based cell process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. is a schematic structural diagram of a perovskite / silicon tandem solar cell with a silicon nanopore array.

[0020] Figure 2 FIG. is the prepared silicon nanopore array structure.

[0021] Figure 3 FIG. is a comparison diagram of spectral absorption between the perovskite / silicon tandem solar cells with a silicon nanopore array in Examples 1, 2, 3, 4 and the planar-structured perovskite / silicon solar cell.

[0022] Figure 4 FIG. is a comparison diagram of the electric field density distribution under the action of 980 nm photons of the perovskite / silicon tandem solar cell with a silicon nanopore array in Example 1.

[0023] Figure 5 FIG. is a comparison diagram of the electric field density distribution under the action of 980 nm photons of the perovskite / silicon tandem solar cell with a silicon nanopore array in Example 2.

[0024] Figure 6 FIG. is a comparison diagram of the electric field density distribution under the action of 980 nm photons of the perovskite / silicon tandem solar cell with a silicon nanopore array in Example 3.

[0025] Figure 7 FIG. is a comparison diagram of the electric field density distribution under the action of 980 nm photons of the perovskite / silicon tandem solar cell with a silicon nanopore array in Example 4.

[0026] Figure 8 FIG. is a comparison diagram of the electric field density distribution under the action of 980 nm photons of the planar-structured perovskite / silicon solar cell.

[0027] Figure 9Comparison diagram of current-voltage test results between the perovskite-silicon tandem solar cells with silicon pore arrays and the planar-structured perovskite-silicon solar cells in Examples 1, 2, 3, 4, and 5. Detailed implementation manners

[0028] The present invention will be further described below in conjunction with embodiments, but it is not intended to limit the present invention.

[0029] Example 1, please refer to Figure 1 and Figure 2 , first, the n-type monocrystalline silicon substrate 1 is selected as an n-type Czochralski monocrystalline silicon wafer with a size of 8 cm × 8 cm, a thickness of 200 μm, and a resistivity of 1.6 Ω·cm. After cleaning, an SiO 2 insulating layer 3 is formed around the surface of the n-type monocrystalline silicon substrate 1 through an oxidation etching process. The exposed area in the middle of the SiO 2 insulating layer 3 is the light-receiving window, with a size of 5 cm × 5 cm. After cleaning and drying with deionized water, it is placed in a diffusion furnace, and high-temperature diffusion is carried out at 1100 °C with BBr 3 liquid boron source to prepare a p-type doped layer 2 to form an emitter region, constituting a PN junction. The concentration of BBr 3 is 12 mg / cm 3 . After taking out the sample, silver nanocolloid is spin-coated on the region where the PN junction is prepared by a spin coater at a rotation speed of 4200 r / min, and the diameter of the silver nanoparticles is 350 nm; the spin-coated silicon wafer is immersed in a hydrogen peroxide solution for etching, the concentration of the solution is 1.2 mol / L, and the time is 0.5 h to form a vertically oriented nanopore periodic array structure 10; the period of the nanopore periodic array structure 10 is 1200 nm, the diameter of the nanopores is 500 nm, the duty cycle is 1 / 3, and the depth is 400 nm. After forming the nanopore periodic array structure 10, the silver nanoparticles are removed with a nitric acid solution. After the sample is cleaned and dried, a TiO 2 thin film layer 4 is prepared on the surface of the sample by spin coating. Titanium isopropoxide is used as the titanium source to prepare a spin coating solution, which is spin-coated at a speed of 2000 r / min, and then annealed and cured. The annealing temperature is 480 °C, the annealing time is 1 h, and the thickness is 100 nm. The TiO 2 does not penetrate into the n-type monocrystalline silicon substrate 1, and the nanopores in the n-type monocrystalline silicon substrate are voids. After annealing and curing, a perovskite absorption layer 5 is prepared on the TiO 2 thin film layer 4 by spin coating. 0.003 mol of CH 3 NH 3 I (purity 99.5%) and 0.003 mol of PbI 2 (purity 99%) are added to a small beaker containing 1 ml of N-dimethylformamide solution. After stirring, CH 3 NH 3 PbI 3Spin coating solution. The perovskite solution is dropped onto the substrate using a spin coater. After leveling the solution, it is placed on a baking machine to solidify the glue for 200 minutes at a solidification temperature range of 85°C, obtaining a perovskite thin film with a thickness of 300 nm to form the perovskite absorption layer 5. Then, a Spiro-OMeTAD hole transport layer 6 with a thickness of 150 nm is set on the perovskite absorption layer 5; an ITO thin film with a thickness of 50 nm is set as the transparent conductive thin film layer 7 on the hole transport layer 6. Finally, an Ag metal electrode 8 with a thickness of 30 nm is deposited on the upper surface of the transparent conductive thin film layer 7 as the lead-out electrode, and an Al metal thin film layer 9 with a thickness of 50 nm is deposited on the lower surface of the n-type monocrystalline silicon substrate 1. The Ag metal electrode 8 and the Al metal thin film layer 9 are used as conductive electrodes to lead out the photo-generated charges to supply power to the external circuit.

[0030] Example 2. Referring to Example 1, first, the n-type monocrystalline silicon substrate 1 is selected as an n-type Czochralski single crystal wafer with a size of 8 cm × 8 cm, a thickness of 200 μm, and a resistivity of 1.6 Ω·cm. After cleaning, a SiO 2 insulating layer 3 is formed around the surface of the n-type monocrystalline silicon substrate 1 through an oxidation etching process. The exposed area in the middle of the SiO 2 insulating layer 3 is the light-receiving window with a size of 5 cm × 5 cm. After cleaning and drying with deionized water, it is placed in a diffusion furnace, and high-temperature diffusion is carried out at 1100°C with liquid boron source BBr 3 to prepare a p-type doping layer 2 to form the emitter region, constituting a PN junction. The concentration of BBr 3 is 12 mg / cm 3 . After taking out the sample, silver nanocolloid is spin-coated on the area where the PN junction is prepared using a spin coater at a rotation speed of 2800 r / min, and the diameter of the silver nanoparticles is 350 nm; the spin-coated silicon wafer is immersed in a hydrogen peroxide solution for etching, the concentration of the solution is 1.2 mol / L, and the time is 0.5 h to form a periodic array structure of vertical nano-pores 10; the period of the periodic array structure of nano-pores 10 is 600 nm, the diameter of the nano-pores is 600 nm, the duty cycle is 2 / 3, and the depth is 400 nm. After forming the periodic array structure of nano-pores 10, the silver nanoparticles are removed with a nitric acid solution. After the sample is cleaned and dried, a TiO 2 thin film layer 4 is prepared by the spin coating method. Titanium isopropoxide is used as the titanium source to prepare a spin coating solution, which is spin-coated at a speed of 2000 r / min, and then annealed. The annealing temperature is 480°C, the annealing time is 1 h, and the thickness is 100 nm. The TiO 2 does not penetrate into the n-type monocrystalline silicon substrate 1, and the nano-pores in the n-type monocrystalline silicon substrate are voids. After annealing and curing, a perovskite absorption layer 5 is prepared on the TiO 2 thin film layer 4 by the spin coating method. 0.003 mol CH 3 NH 3 I (purity 99.5%) and 0.003 mol PbI 2(With a purity of 99%) was added to a small beaker containing 1 ml of N-dimethylformamide solution. After stirring, CH 3 NH 3 PbI 3 spin coating solution. The perovskite solution was dropped on the substrate using a spin coater. After spin coating, it was placed on a baking machine to solidify the glue for 200 minutes at a solidification temperature range of 85 °C to obtain a perovskite thin film with a thickness of 300 nm to form the perovskite absorption layer 5. Then, a Spiro-OMeTAD hole transport layer 6 with a thickness of 150 nm was provided on the perovskite absorption layer 5; a 50-nm ITO thin film was provided as a transparent conductive thin film layer 7 on the hole transport layer 6. Finally, an Ag metal electrode 8 with a thickness of 30 nm was deposited on the upper surface of the transparent conductive thin film layer 7 as an extraction electrode. An Al metal thin film layer 9 with a thickness of 50 nm was deposited on the lower surface of the n-type monocrystalline silicon substrate 1. The Ag metal electrode 8 and the Al metal thin film layer 9 were used as conductive electrodes to extract photo-generated charges to supply power to the external circuit.

[0031] Example 3. Referring to Example 1, first, the n-type monocrystalline silicon substrate 1 was selected as an n-type Czochralski monocrystalline silicon wafer with a size of 8 cm × 8 cm, a thickness of 200 μm, and a resistivity of 1.6 Ω·cm. After cleaning, a SiO 2 insulating layer 3 was formed around the surface of the n-type monocrystalline silicon substrate 1 through an oxidation etching process. The exposed area in the middle of the SiO 2 insulating layer 3 was the light-receiving window with a size of 5 cm × 5 cm. After cleaning and drying with deionized water, it was placed in a diffusion furnace, and high-temperature diffusion was carried out at 1100 °C with BBr 3 liquid boron source to prepare a p-type doping layer 2 to form an emitter region, constituting a PN junction. The concentration of BBr 3 was 12 mg / cm 3 . After taking out the sample, silver nanocolloid was spin-coated on the region where the PN junction was prepared using a spin coater at a rotation speed of 2800 r / min, and the diameter of the silver nanoparticles was 350 nm; the spin-coated silicon wafer was immersed in a hydrogen peroxide solution for etching, the concentration of the solution was 1.5 mol / L, and the time was 1.5 h to form a periodic array structure 10 of nano-pores in the vertical direction; the period of the periodic array structure 10 of nano-pores was 800 nm, the diameter of the nano-pores was 400 nm, the duty cycle was 2 / 3, and the depth was 800 nm. After forming the periodic array structure 10 of nano-pores, the silver nanoparticles were removed with a nitric acid solution. After the sample was cleaned and dried, a TiO 2 thin film layer 4 was prepared by the spin coating method. Titanium isopropoxide was used as a titanium source to prepare a spin coating solution, which was spin-coated at a speed of 2000 r / min, and then annealed at an annealing temperature of 480 °C for an annealing time of 1 h, with a thickness of 100 nm. The TiO 2 did not penetrate into the n-type monocrystalline silicon substrate 1, and the nano-pores in the n-type monocrystalline silicon substrate were voids. After annealing and curing, on the TiO 2The perovskite absorption layer 5 is prepared on the thin film layer 4 by spin coating. 0.003 mol of CH 3 NH 3 I (purity 99.5%) and 0.003 mol of PbI 2 (purity 99%) are added to a small beaker containing 1 ml of N-dimethylformamide solution. After stirring, the CH 3 NH 3 PbI 3 spin coating solution is obtained. The perovskite solution is dropped on the substrate by a spin coater, and after leveling, it is placed on a baking machine to solidify the glue for 200 minutes at a solidification temperature range of 85 °C to obtain a perovskite thin film with a thickness of 300 nm to form the perovskite absorption layer 5. Then, a Spiro-OMeTAD hole transport layer 6 with a thickness of 150 nm is set on the perovskite absorption layer 5; a 50-nm ITO thin film is set as the transparent conductive thin film layer 7 on the hole transport layer 6. Finally, an Ag metal electrode 8 with a thickness of 30 nm is deposited on the upper surface of the transparent conductive thin film layer 7 as the lead-out electrode, and an Al metal thin film layer 9 with a thickness of 50 nm is deposited on the lower surface of the n-type monocrystalline silicon substrate 1. The Ag metal electrode 8 and the Al metal thin film layer 9 are used as conductive electrodes to lead out photo-generated charges to supply power to the external circuit.

[0032] Example 4. Referring to Example 1, first, the n-type monocrystalline silicon substrate 1 is selected as an n-type Czochralski single crystal silicon wafer with a size of 8 cm × 8 cm, a thickness of 200 μm, and a resistivity of 1.6 Ω·cm. After cleaning, a SiO 2 insulating layer 3 is formed around the surface of the n-type monocrystalline silicon substrate 1 through an oxidation and etching process. The exposed area in the middle of the SiO 2 insulating layer 3 is the light-receiving window with a size of 5 cm × 5 cm. After cleaning and drying with deionized water, it is placed in a diffusion furnace, and high-temperature diffusion is carried out at 1100 °C with BBr 3 liquid boron source to prepare a p-type doping layer 2 to form an emitter region, constituting a PN junction. The BBr 3 concentration is 12 mg / cm 3 . After taking out the sample, silver nanocolloid is spin-coated on the region where the PN junction is prepared by a spin coater at a rotation speed of 2800 r / min, and the diameter of the silver nanoparticles is 350 nm; the spin-coated silicon wafer is immersed in a hydrogen peroxide solution for etching, the concentration of the solution is 1.5 mol / L, and the time is 1.2 h to form a vertical nanohole periodic array structure 10; the period of the nanohole periodic array structure 10 is 600 nm, the diameter of the nanohole is 400 nm, the duty cycle is 2 / 3, and the depth is 600 nm. After forming the nanohole periodic array structure 10, the silver nanoparticles are removed with a nitric acid solution. After the sample is cleaned and dried, TiO 2The thin film layer 4 is prepared by spin-coating a solution with titanium isopropoxide as the titanium source at a speed of 2000 r / min, and then annealing. The annealing temperature is 480 °C, the annealing time is 1 h, and the thickness is 100 nm. TiO 2 It does not penetrate into the n-type single-crystalline silicon substrate 1, and the nanopores in the n-type single-crystalline silicon substrate are voids. After annealing and curing, on the TiO 2 thin film layer 4, a perovskite absorption layer 5 is prepared by spin-coating method. 0.003 mol of CH 3 NH 3 I (purity 99.5%) and 0.003 mol of PbI 2 (purity 99%) are added to a small beaker containing 1 ml of N-dimethylformamide solution. After stirring, a CH 3 NH 3 PbI 3 spin-coating solution is obtained. The perovskite solution is dropped on the substrate by a spin coater, and after spin-coating, it is placed on a baking machine to solidify the glue for 200 minutes. The solidification temperature range is 85 °C, and a perovskite thin film with a thickness of 300 nm is obtained to form the perovskite absorption layer 5. Then, a Spiro-OMeTAD hole transport layer 6 with a thickness of 150 nm is set on the perovskite absorption layer 5; a 50-nm ITO thin film is set as the transparent conductive thin film layer 7 on the hole transport layer 6. Finally, an Ag metal electrode 8 with a thickness of 30 nm is deposited on the upper surface of the transparent conductive thin film layer 7 as the lead-out electrode, and an Al metal thin film layer 9 with a thickness of 50 nm is deposited on the lower surface of the n-type single-crystalline silicon substrate 1. The Ag metal electrode 8 and the Al metal thin film layer 9 are used as conductive electrodes to lead out photo-generated charges to supply power to the external circuit.

[0033] Example 5, referring to Example 1, first, the n-type single-crystalline silicon substrate 1 is selected as an n-type Czochralski single-crystalline silicon wafer with a size of 8 cm × 8 cm, a thickness of 200 μm, and a resistivity of 1.2 Ω·cm. After cleaning, a SiO 2 insulating layer 3 is formed around the surface of the n-type single-crystalline silicon substrate 1 through an oxidation and etching process. The exposed area in the middle of the SiO 2 insulating layer 3 is the light-receiving window, with a size of 5 cm × 5 cm. After cleaning and drying with deionized water, it is placed in a diffusion furnace, and high-temperature diffusion is carried out at 1200 °C with liquid boron source BBr 3 to prepare a p-type doping layer 2 to form an emitter region, constituting a PN junction. The concentration of BBr 3 is 15 mg / cm 3。After taking out the sample, a silver nanocolloid was spin-coated on the area where the PN junction was prepared using a spin coater at a rotation speed of 2800 r / min, and the diameter of the silver nanoparticles was 350 nm; the spin-coated silicon wafer was immersed in a hydrogen peroxide solution for etching, the concentration of the solution was 1.5 mol / L, and the time was 1.2 h to form a periodic array structure of nanoholes 10 in the vertical direction; the period of the periodic array structure of nanoholes 10 was 600 nm, the diameter of the nanoholes was 400 nm, the duty cycle was 2 / 3, and the depth was 600 nm. After forming the periodic array structure of nanoholes 10, the silver nanoparticles were removed with a nitric acid solution. After the sample was cleaned and dried, TiO 2 thin film layer 4 was prepared by spin coating using titanium isopropoxide as the titanium source to prepare a spin coating solution, which was spin coated at a speed of 2500 r / min, and then annealed. The annealing temperature was 650 °C, the annealing time was 1 h, and the thickness was 200 nm. TiO 2 did not penetrate into the n-type single-crystalline silicon substrate 1, and the nanoholes in the n-type single-crystalline silicon substrate were voids. After annealing and curing, on the TiO 2 thin film layer 4, a perovskite absorption layer 5 was prepared by spin coating. 0.003 mol of CH 3 NH 3 I (purity 99.5%) and 0.003 mol of PbI 2 (purity 99%) were added to a small beaker containing 1 ml of N-dimethylformamide solution. After stirring, a CH 3 NH 3 PbI 3 spin coating solution was obtained. The perovskite solution was dropped on the substrate using a spin coater, and after leveling, it was placed on a baking machine to solidify the glue for 200 minutes. The solidification temperature range was 85 °C to obtain a perovskite thin film with a thickness of 300 nm to form the perovskite absorption layer 5. Then, a Spiro-OMeTAD hole transport layer 6 with a thickness of 150 nm was set on the perovskite absorption layer 5; a 50-nm ITO thin film was set as the transparent conductive thin film layer 7 on the hole transport layer 6. Finally, an Ag metal electrode 8 with a thickness of 30 nm was deposited on the upper surface of the transparent conductive thin film layer 7 as the lead-out electrode, and an Al metal thin film layer 9 with a thickness of 50 nm was deposited on the lower surface of the n-type single-crystalline silicon substrate 1. The Ag metal electrode 8 and the Al metal thin film layer 9 were used as conductive electrodes to lead out photo-generated charges to supply power to the external circuit.

[0034] The comparative example was a planar-structured perovskite silicon-based solar cell, from Figure 3It can be seen that, compared with the comparative examples, in Examples 1, 2, 3, and 4, after using the silicon pore array as the bottom cell structure, the photon absorption efficiency in the entire solar wavelength band (300 - 1100 nm) has increased. Thanks to the resonant absorption of long-wavelength photons, especially the absorption rate of photons in the near-infrared region in the range of 700 - 1100 nm has increased significantly. The increase in the photon absorption efficiency of Example 5 in the entire solar wavelength band (300 - 1100 nm) is similar to that of Example 4 (since it cannot be effectively distinguished from Example 4 in the figure, it is not shown).

[0035] From Figures 4 to 8 the absorption electric field density of 980 nm photons, it can be seen that, compared with the comparative example, the resonant light absorption modes of Examples 1, 2, 3, and 4 have all been enhanced. Among them, through the process optimization of the pore diameter, depth, and period of the nanopore array, the resonant absorption of Example 4 at this wavelength is the best.

[0036] From Figure 5 it can be seen that, compared with the comparative example, in Examples 1, 2, 3, and 4, the short-circuit current density has increased from 5.73 mA / cm 2 to 7.45 mA / cm 2 , 8.27 mA / cm 2 , 10.61 mA / cm 2 and 12.81 mA / cm 2 , indicating that the introduction of the nanopore array structure has significantly improved the photon absorption efficiency; on the basis of Example 4, by adjusting the process parameters of the n-type single-crystalline silicon substrate 1 and the p-type doping layer 2, the short-circuit current density of Example 5 has increased to 13.55 mA / cm 2 , indicating that the PN junction region with the nanopore array structure can significantly affect the separation and collection efficiency of photo-generated carriers, and the optoelectronic conversion efficiency of the device has been improved after optimization.

Claims

1. A silicon-based tandem solar cell, comprising a bottom cell structure and a top cell structure, characterized in that, The top cell structure is stacked on the bottom cell structure. The bottom cell structure includes an n-type monocrystalline silicon substrate, and SiO is provided around the upper surface of the n-type monocrystalline silicon substrate 2 insulating layer to form a light-receiving window in the central region of the n-type monocrystalline silicon substrate. A p-type doping layer is prepared on the n-type monocrystalline silicon substrate in the light-receiving window region. A periodic array structure of vertical nanoholes is etched and prepared in the stacked region of the p-type doping layer and the n-type monocrystalline silicon substrate. The period of the periodic array structure of nanoholes is 600-1200 nm, the diameter of the nanoholes in the periodic array structure of nanoholes is 400-600 nm, the depth is 400-800 nm, the duty cycle of the periodic array structure of nanoholes is 1 / 3-2 / 3, the nanoholes in the n-type monocrystalline silicon substrate are voids, and a metal thin film layer is provided on the lower surface of the n-type monocrystalline silicon substrate; the top cell structure sequentially includes TiO from bottom to top 2 thin film layer, perovskite absorption layer, hole transport layer, transparent conductive thin film layer and metal electrode; the metal electrode and the metal thin film layer are respectively led out as conductive electrodes to supply power to the external circuit. The TiO 2 thin film layer has a thickness of 50-300 nm, and the perovskite absorption layer has a thickness of 100-500 nm.

2. The silicon-based tandem solar cell according to claim 1, characterized in that, the hole transport layer is one of nickel oxide, tungsten oxide, and Spiro-OMeTAD, and the thickness is 150 - 800 nm.

3. The silicon-based tandem solar cell according to claim 1, characterized in that, the material of the metal electrode is one of Au, Ag, Al, Gu, and Pt, and the thickness is 10 - 500 nm.

4. A method for preparing a silicon-based tandem solar cell, characterized in that, The steps include:

1. Depositing a layer of SiO on the n-type single crystal silicon substrate 2 The method comprises the following steps: first, forming a light receiving window through an insulating layer; second, preparing a PN junction on the surface of an n-type single crystal silicon substrate in the light receiving window region by high temperature diffusion of a liquid boron source; third, preparing a vertical nanopore periodic array structure on the PN junction by a metal-assisted chemical etching method, wherein the period of the nanopore periodic array structure is 600-1200nm, the diameter of the nanopores of the nanopore periodic array structure is 400-600nm, the depth is 400-800nm, and the duty ratio of the nanopore periodic array structure is 1 / 3-2 / 3; IV. Prepare a TiO thin film layer as an electron transport layer by spin coating method; V. Perform annealing and curing, and sequentially prepare a perovskite absorption layer and a hole transport layer on the TiO thin film layer by spin coating method; 2 thin film layer; V. Perform annealing and curing, and sequentially prepare a perovskite absorption layer and a hole transport layer on the TiO 2 thin film layer by spin coating method; VI. A transparent conductive thin film layer and a metal electrode are respectively prepared on the surface of the hole transport layer by an electron beam evaporation process; VII. A metal thin film layer is deposited on the lower surface of the n-type monocrystalline silicon substrate to lead out a wire as the negative electrode of the silicon-based tandem solar cell, and the wire led out from the metal electrode is used as the positive electrode of the silicon-based tandem solar cell.

5. The method for preparing a silicon-based tandem solar cell according to claim 4, characterized in that, during the process of preparing the vertically-aligned nanopore periodic array structure by using the metal-assisted chemical etching method, a silver nanocolloid is spin-coated on the silicon wafer for preparing the PN junction by a spin coater at a rotational speed of 2500 - 5000 r / min, and the diameter of the silver nanoparticles is 50 - 800 nm; after spin coating, it is immersed in a hydrogen peroxide solution for etching, the concentration of the solution is 0.2 - 2 mol / L, and the time is 0.5 - 2 h; after forming the nanopore periodic array structure, the silver nanoparticles are removed with a nitric acid solution.

6. The method for preparing a silicon-based tandem solar cell according to claim 4, characterized in that, The resistivity of the n-type monocrystalline silicon substrate is 1.2 to 1.3 Ω·cm. When preparing the PN junction by high-temperature diffusion using liquid boron source, BBr with a concentration of 15 to 16 mg / cm 3 is used as the liquid boron source, and high-temperature diffusion is carried out at 1200 to 1250 °C to prepare the p-type doping layer. 3 ​ 7. The method for preparing a silicon-based tandem solar cell according to claim 4, characterized in that, When preparing the TiO 2 thin film layer by spin coating method, titanium isopropoxide is used as the titanium source to prepare the spin coating solution, and spin coating is carried out at a speed of 2000-3500 r / min. When annealing and curing, the annealing temperature is 380-650 °C and the annealing time is 1-3 h. The thickness of the TiO 2 thin film layer is 10-300 nm.

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