A method for preparing a heterojunction solar cell

Abstract

The present invention relates to the technical field of solar cells, and discloses a preparation method of a heterojunction solar cell. The steps are as follows: cleaning and texturing; depositing an intrinsic amorphous silicon layer and a doped microcrystalline silicon layer; depositing an ITO transparent conductive layer; depositing a nitrogen-doped TiO2 layer; depositing a nitrogen-doped SiO2 layer; printing a silver paste electrode, and drying and sintering at a low temperature. In the present invention, a three-layer antireflection film of ITO / TiO2 / SiO2 is formed on the surface of the heterojunction solar cell under low-temperature annealing, and the TiO2 / SiO2 stack is subjected to nitrogen doping treatment. The process is simple, and at the same time, the antireflection effect can be significantly improved, and a large current gain is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a method for preparing a heterojunction solar cell. Background Art

[0002] A heterojunction cell is a new type of solar cell that utilizes the potential difference generated by the electron energy level difference at the interface of the p-n junctions of different semiconductor materials. Heterojunction cells have advantages such as good passivation effect, high open-circuit voltage, high conversion efficiency, and low temperature coefficient, and have currently become a research hotspot for high-efficiency and low-cost solar cells.

[0003] How to improve the photoelectric conversion efficiency of solar cells has always been a problem that the solar photovoltaic industry is committed to researching, and the light reflection loss on the surface of solar cells is an important factor restricting the improvement of the photoelectric conversion efficiency of solar cells. An antireflection film can effectively reduce the light reflection loss on the silicon surface, thereby improving the conversion efficiency of solar cells. Indium tin oxide (ITO) thin film, as a transparent conductive oxide thin film, has excellent conductivity and chemical stability, and is a very important antireflection film in crystalline silicon heterojunction solar cells, usually used as a single-layer film. However, its average visible light transmittance is relatively low (less than 90%), and there are parasitic absorption losses and reflection losses in the ultraviolet and near-infrared regions, reducing the efficiency of the cell.

[0004] Therefore, in the prior art, materials such as SiO x , TiO2 or SiN x are used to form a double-layer or multi-layer antireflection film on the surface of the ITO film to enhance the antireflection effect, thereby improving the photoelectric conversion efficiency of the heterojunction solar cell. SiN x is a commonly used antireflection material in crystalline silicon solar cells, which has high light transmittance and excellent passivation performance, and can significantly improve the spectral response of the internal quantum efficiency in the short-wavelength range and improve the photoelectric conversion efficiency. However, the low-temperature process of heterojunction cells limits the annealing temperature not to exceed 250°C. If the SiN x thin film is directly deposited on the surface of the ITO thin film at this temperature, the low-temperature silver paste cannot penetrate the SiN xThe dielectric layer causes an increase in the series resistance of the battery, affecting the collection of carriers. TiO2 has a good antireflection effect on crystalline silicon solar cells, but it has no hydrogen passivation effect, so that the open-circuit voltage of solar cells using TiO2 thin film as an antireflection film is low, and it is difficult to improve the photoelectric conversion efficiency. SiO2 has excellent passivation effect, but its refractive index is relatively low and the antireflection effect is not good. Therefore, in the prior art, a stacked antireflection structure of TiO2 / SiO2 is generally used to achieve the dual effects of antireflection and passivation. However, the existing TiO2 / SiO2 stacked antireflection structure used in heterojunction cells has limited antireflection effect, and the current gain effect needs to be further improved. Summary of the Invention

[0005] The present invention is to overcome the above problems existing in the antireflection film of heterojunction solar cells in the prior art, and provides a preparation method of a heterojunction solar cell, forming an ITO / TiO2 / SiO2 three-layer antireflection film on the surface of the heterojunction solar cell under low-temperature annealing. The TiO2 / SiO2 stack is subjected to nitrogen doping treatment. The process is simple, and at the same time, the antireflection effect can be significantly improved, and a large current gain is obtained.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a heterojunction solar cell, comprising the following steps:

[0008] (1) Cleaning and texturing the silicon wafer to form a textured layer on the front and back surfaces of the silicon wafer;

[0009] (2) Sequentially depositing an intrinsic amorphous silicon layer and a doped microcrystalline silicon layer on the front and back surfaces of the textured silicon wafer; the front surface is an N-type doped microcrystalline silicon layer, and the back surface is a P-type doped microcrystalline silicon layer;

[0010] (3) Depositing an ITO transparent conductive layer on the surface of the doped microcrystalline silicon layer on the front and back surfaces of the silicon wafer;

[0011] (4) By ALD method, using TiCl4, H2O and NH3 as Ti source, O source and N source respectively, and using nitrogen and argon as purge gas and carrier gas respectively, depositing a nitrogen-doped TiO2 layer on the surface of the ITO transparent conductive layer on the front surface of the silicon wafer;

[0012] (5) By PECVD method, using SiH4-N2O gas to deposit a nitrogen-doped SiO2 layer on the surface of the nitrogen-doped TiO2 layer;

[0013] (6) Printing silver paste electrodes on the surface of the nitrogen-doped SiO2 layer on the front surface and the ITO transparent conductive layer on the back surface, drying and sintering to obtain the heterojunction solar cell.

[0014] In the present invention, a nitrogen-doped TiO2 layer and a nitrogen-doped SiO2 layer are deposited on the surface of the ITO transparent conductive layer on the front side of the heterojunction battery to form an ITO / TiO2 / SiO2 stacked antireflection film. On the one hand, the ITO process window is broadened, the antireflection pressure of the ITO film is reduced, its film thickness is decreased, and the battery cost is lowered. On the other hand, in the stacked antireflection film of the present invention, the refractive index of the ITO layer is the highest, the refractive index of the nitrogen-doped TiO2 layer is higher than that of the nitrogen-doped SiO2 layer, and the design of the gradient refractive index can reduce the reflection loss on the battery surface. At the same time, in the present invention, TiCl4, H2O and NH3 are used as the Ti source, O source and N source respectively, and the ALD process is adopted to prepare the nitrogen-doped TiO2 layer, and SiH4-N2O gas is used, and the PECVD process is adopted to prepare the nitrogen-doped SiO2 layer; nitrogen doping can assist oxygen elements to optimize the energy band structure, reduce the recombination defects and improve the minority carrier lifetime, which can further increase the transmittance of the antireflection film, optimize the optical performance of the heterojunction battery, and obtain a large current gain.

[0015] Preferably, in step (3), the thickness of the front ITO transparent conductive layer is 50-80 nm, and the thickness of the back ITO transparent conductive layer is 80-140 nm; in step (4), the thickness of the nitrogen-doped TiO2 layer is 25-50 nm; in step (5), the thickness of the nitrogen-doped SiO2 layer is 50-90 nm.

[0016] Preferably, in step (4), the growth cycle parameters of the nitrogen-doped TiO2 layer are: TiCl4 injection for 5-10 s, nitrogen purge for 25-35 s, H2O injection for 8-14 s, nitrogen purge for 10-15 s, NH3 injection for 15-25 s, nitrogen purge for 8-12 s; the NH3 flow rate is 90-110 sccm, the nitrogen flow rate is 180-220 sccm; the growth temperature is 210-220 °C, and the pressure in the reaction chamber is 4-6 mbar.

[0017] Preferably, in step (5), the flow ratio of N2O and SiH4 during the deposition of the nitrogen-doped SiO2 layer is 1-3, the temperature is 210-230 °C, the pressure in the chamber is 15-20 Pa, and the deposition power is 850-1000 W.

[0018] By controlling the parameters during the deposition of the nitrogen-doped TiO2 layer and the nitrogen-doped SiO2 layer, the nitrogen doping amounts of the TiO2 layer and the SiO2 layer can be controlled within an appropriate range. If the nitrogen doping amount is too small, the improvement effect on the transmittance of the antireflection film is not obvious; while if the nitrogen doping amount is too large, it will affect the electron transport performance, and the film layer structure is too loose, which is also not conducive to the improvement of the film performance.

[0019] Preferably, in step (3), the ITO transparent conductive layer is deposited by PVD or RPD method.

[0020] Preferably, the thickness of the silicon wafer used in step (1) is 80 - 180 μm.

[0021] Preferably, the thickness of the intrinsic amorphous silicon layers on the front and back sides of the silicon wafer in step (2) is 3 - 15 nm.

[0022] Preferably, the thickness of the N-type doped microcrystalline silicon layer on the front side in step (2) is 10 - 40 nm, and the thickness of the P-type doped microcrystalline silicon layer on the back side is 15 - 45 nm.

[0023] Preferably, in step (2), the intrinsic amorphous silicon layer and the doped microcrystalline silicon layer are deposited by PECVD, HWCVD or LPCVD method.

[0024] Preferably, the sintering temperature in step (6) is lower than 300 °C.

[0025] Therefore, the present invention has the following beneficial effects:

[0026] (1) In the heterojunction battery, the ITO / TiO2 / SiO2 stacked antireflection film is adopted. On the one hand, the ITO process window is broadened, and the antireflection pressure of the ITO film is reduced, so that its film thickness is decreased; on the other hand, the design of the gradient refractive index can reduce the reflection loss on the battery surface;

[0027] (2) When preparing the TiO2 and SiO2 layers, the nitrogen doping process is used to increase the transmittance of the antireflection film and optimize the optical performance;

[0028] (3) The low-temperature process is used throughout the process, and the passivation layer will not be damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of the heterojunction solar cell of the present invention.

[0030] In the figure: 1 - silicon wafer substrate, 2 - intrinsic amorphous silicon layer, 3 - P-type doped microcrystalline silicon layer, 4 - N-type doped microcrystalline silicon layer, 5 - ITO transparent conductive layer, 6 - nitrogen-doped TiO2 layer, 7 - nitrogen-doped SiO2 layer, 8 - electrode. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further described below in conjunction with the drawings and the detailed implementation manners.

[0032] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in this field.

[0033] General embodiment:

[0034] A heterojunction solar cell, the structure of which is as Figure 1As shown, the preparation method includes the following steps:

[0035] (1) Clean and texture the silicon wafer to form a textured layer on the front and back surfaces of the silicon wafer, obtaining the silicon wafer substrate 1;

[0036] (2) Sequentially deposit an intrinsic amorphous silicon layer 2 and a doped microcrystalline silicon layer on the front and back surfaces of the textured silicon wafer; the front is an N-type doped microcrystalline silicon layer 4, and the back is a P-type doped microcrystalline silicon layer 3;

[0037] (3) Deposit an ITO transparent conductive layer 5 on the surfaces of the doped microcrystalline silicon layers on the front and back surfaces of the silicon wafer;

[0038] (4) By the ALD method, using TiCl4, H2O, and NH3 as the Ti source, O source, and N source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, deposit a nitrogen-doped TiO2 layer 6 on the surface of the ITO transparent conductive layer on the front surface of the silicon wafer;

[0039] (5) By the PECVD method, use SiH4-N2O gas to deposit a nitrogen-doped SiO2 layer 7 on the surface of the nitrogen-doped TiO2 layer;

[0040] (6) Print silver paste as the electrode 8 on the surfaces of the nitrogen-doped SiO2 layer on the front and the ITO transparent conductive layer on the back, and obtain the heterojunction solar cell after drying and sintering.

[0041] As a preferred solution, the thickness of the silicon wafer used in step (1) is 80 - 180 μm.

[0042] As a preferred solution, in step (2), the intrinsic amorphous silicon layer and the doped microcrystalline silicon layer are deposited by the PECVD, HWCVD, or LPCVD method; the thickness of the intrinsic amorphous silicon layer on the front and back surfaces of the silicon wafer is 3 - 15 nm, the thickness of the N-type doped microcrystalline silicon layer on the front is 10 - 40 nm, and the thickness of the P-type doped microcrystalline silicon layer on the back is 15 - 45 nm.

[0043] As a preferred solution, in step (3), the ITO transparent conductive layer is deposited by the PVD or RPD method, the thickness of the ITO transparent conductive layer on the front is 50 - 80 nm, and the thickness of the ITO transparent conductive layer on the back is 80 - 140 nm.

[0044] As a preferred solution, in step (4), the thickness of the nitrogen-doped TiO2 layer is 25 - 50 nm, and the growth cycle parameters are: TiCl4 injection for 5 - 10 s, nitrogen purge for 25 - 35 s, H2O injection for 8 - 14 s, nitrogen purge for 10 - 15 s, NH3 injection for 15 - 25 s, nitrogen purge for 8 - 12 s; the NH3 flow rate is 90 - 110 sccm, the nitrogen flow rate is 180 - 220 sccm; the growth temperature is 210 - 220 °C, and the pressure in the reaction chamber is 4 - 6 mbar.

[0045] As a preferred solution, in step (5), the thickness of the nitrogen-doped SiO2 layer is 50 - 90 nm; the flow rate ratio of N2O to SiH4 during deposition is 0.2 - 3, the temperature is 210 - 230 °C, the chamber pressure is 15 - 20 Pa, and the deposition power is 850 - 1000 W.

[0046] As a preferred solution, the sintering temperature in step (6) is lower than 300 °C.

[0047] Example 1:

[0048] A method for preparing a heterojunction solar cell, comprising the following steps:

[0049] (1) Take a silicon wafer with a thickness of 110 μm and a size of 210×105 mm. After the cleaning process, remove the organic dirt, metal impurities and surface damage layer on the silicon wafer surface; after cleaning, use an alkaline solution to texture the silicon wafer to form a textured layer on the front and back surfaces of the silicon wafer;

[0050] (2) By PECVD method, deposit an intrinsic amorphous silicon layer with a thickness of 6 nm on the front and back surfaces of the textured silicon wafer in sequence;

[0051] (3) By PECVD method, deposit an N-type doped microcrystalline silicon layer with a thickness of 30 nm on the surface of the intrinsic amorphous silicon layer on the front surface of the silicon wafer;

[0052] (4) By PECVD method, deposit a P-type doped microcrystalline silicon layer with a thickness of 40 nm on the surface of the intrinsic amorphous silicon layer on the back surface of the silicon wafer;

[0053] (5) Use a PVD device to deposit an ITO transparent conductive layer on the surfaces of the doped microcrystalline silicon layers on the front and back surfaces of the silicon wafer; the thickness of the ITO transparent conductive layer on the front surface is 60 nm, and the thickness of the ITO transparent conductive layer on the back surface is 105 nm;

[0054] (6) By ALD method, using TiCl4, H2O and NH3 as the Ti source, O source and N source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, deposit a nitrogen-doped TiO2 layer with a thickness of 30 nm on the surface of the ITO transparent conductive layer on the front surface of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, NH3 injection for 20 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the reaction chamber pressure is 5 mbar;

[0055] (7) By PECVD method, a nitrogen-doped SiO2 layer with a thickness of 60 nm is deposited on the surface of the nitrogen-doped TiO2 layer using SiH4-N2O gas; the flow ratio of N2O to SiH4 is 2, the temperature is 230 °C, the chamber pressure is 20 Pa, and the deposition power is 1000 W;

[0056] (8) Screen printing method is used to print silver paste electrodes on the surface of the nitrogen-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side. After low-temperature drying at 150 °C, it is sintered at 200 °C, burning through the surface nitrogen-doped TiO2 layer and the nitrogen-doped SiO2 layer to contact the ITO layer; the obtained heterojunction solar cell adopts a multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0057] Example 2:

[0058] A preparation method of a heterojunction solar cell, comprising the following steps:

[0059] Steps (1) to (5) are the same as those in Example 1;

[0060] (6) By ALD method, using TiCl4, H2O and NH3 as Ti source, O source and N source respectively, and using nitrogen and argon as purge gas and carrier gas respectively, a nitrogen-doped TiO2 layer with a thickness of 50 nm is deposited on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 5 s, nitrogen purge for 30 s, H2O injection for 8 s, nitrogen purge for 12 s, NH3 injection for 16 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the reaction chamber pressure is 5 mbar;

[0061] (7) By PECVD method, a nitrogen-doped SiO2 layer with a thickness of 50 nm is deposited on the surface of the nitrogen-doped TiO2 layer using SiH4-N2O gas; the flow ratio of N2O to SiH4 is 1.8, the temperature is 230 °C, the chamber pressure is 20 Pa, and the deposition power is 1000 W;

[0062] (8) Screen printing method is used to print silver paste electrodes on the surface of the nitrogen-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side. After low-temperature drying at 150 °C, it is sintered at 200 °C, burning through the surface nitrogen-doped TiO2 layer and the nitrogen-doped SiO2 layer to contact the ITO layer; the obtained heterojunction solar cell adopts a multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0063] Example 3:

[0064] A preparation method of a heterojunction solar cell, comprising the following steps:

[0065] Steps (1) to (5) are the same as those in Example 1;

[0066] (6) By ALD method, using TiCl4, H2O and NH3 as Ti source, O source and N source respectively, and using nitrogen and argon as purge gas and carrier gas respectively, deposit a 25-nm-thick N-doped TiO2 layer on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 10 s, nitrogen purge for 30 s, H2O injection for 14 s, nitrogen purge for 12 s, NH3 injection for 24 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the pressure in the reaction chamber is 5 mbar;

[0067] (7) By PECVD method, deposit a 90-nm-thick N-doped SiO2 layer on the surface of the N-doped TiO2 layer using SiH4-N2O gas; the flow ratio of N2O and SiH4 is 2, the temperature is 210 °C, the pressure in the chamber is 20 Pa, and the deposition power is 1000 W;

[0068] (8) Use screen printing method to print silver paste electrodes on the surface of the N-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side, dry at low temperature at 150 °C and then sinter at 200 °C to burn through the surface N-doped TiO2 layer and the N-doped SiO2 layer to contact the ITO layer; obtain the heterojunction solar cell, the cell pattern adopts a multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0069] Example 4:

[0070] A preparation method of a heterojunction solar cell, comprising the following steps:

[0071] Steps (1) to (5) are the same as those in Example 1;

[0072] (6) By ALD method, using TiCl4, H2O and NH3 as Ti source, O source and N source respectively, and using nitrogen and argon as purge gas and carrier gas respectively, deposit a 30-nm-thick N-doped TiO2 layer on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, NH3 injection for 20 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the pressure in the reaction chamber is 5 mbar;

[0073] (7) By PECVD method, deposit a 60-nm-thick N-doped SiO2 layer on the surface of the N-doped TiO2 layer using SiH4-N2O gas; the flow ratio of N2O and SiH4 is 1, the temperature is 230 °C, the pressure in the chamber is 15 Pa, and the deposition power is 1000 W;

[0074] (8) The silver paste electrodes are printed on the surface of the nitrogen-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side by screen printing method, dried at a low temperature of 150 °C and then sintered at 200 °C, burning through the surface nitrogen-doped TiO2 layer and the nitrogen-doped SiO2 layer to contact the ITO layer; the heterojunction solar cell is obtained, and the cell pattern adopts the multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0075] Example 5:

[0076] A method for preparing a heterojunction solar cell, comprising the following steps:

[0077] Steps (1) to (5) are the same as those in Example 1;

[0078] (6) By ALD method, using TiCl4, H2O and NH3 as Ti source, O source and N source respectively, and using nitrogen and argon as purge gas and carrier gas respectively, deposit a nitrogen-doped TiO2 layer with a thickness of 30 nm on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, NH3 injection for 20 s, nitrogen purge for 10 s; the flow rate of NH3 is 100 sccm, the flow rate of nitrogen is 200 sccm; the growth temperature is 220 °C, and the pressure in the reaction chamber is 5 mbar;

[0079] (7) By PECVD method, use SiH4-N2O gas to deposit a nitrogen-doped SiO2 layer with a thickness of 60 nm on the surface of the nitrogen-doped TiO2 layer; the flow ratio of N2O and SiH4 is 2, the temperature is 230 °C, the pressure in the chamber is 15 Pa, and the deposition power is 850 W;

[0080] (8) The silver paste electrodes are printed on the surface of the nitrogen-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side by screen printing method, dried at a low temperature of 150 °C and then sintered at 200 °C, burning through the surface nitrogen-doped TiO2 layer and the nitrogen-doped SiO2 layer to contact the ITO layer; the heterojunction solar cell is obtained, and the cell pattern adopts the multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0081] Example 6:

[0082] A method for preparing a heterojunction solar cell, comprising the following steps:

[0083] Steps (1) to (5) are the same as those in Example 1;

[0084] (6) By the ALD method, using TiCl4, H2O, and NH3 as the Ti source, O source, and N source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, deposit a 30-nm-thick N-doped TiO2 layer on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, NH3 injection for 20 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the pressure in the reaction chamber is 5 mbar;

[0085] (7) By the PECVD method, deposit a 60-nm-thick N-doped SiO2 layer on the surface of the N-doped TiO2 layer using SiH4-N2O gas; the flow ratio of N2O to SiH4 is 3, the temperature is 230 °C, the pressure in the chamber is 15 Pa, and the deposition power is 1000 W;

[0086] (8) Use screen printing to print silver paste electrodes on the surface of the N-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side, dry at a low temperature of 150 °C and then sinter at 200 °C to burn through the surface N-doped TiO2 layer and the N-doped SiO2 layer to contact the ITO layer; obtain the heterojunction solar cell, the cell pattern adopts a multi-main grid line technical solution, and the number of main grid lines of the cell is 18BB.

[0087] Comparative Example 1 (without setting the TiO2 / SiO2 layer):

[0088] A method for preparing a heterojunction solar cell, comprising the following steps:

[0089] (1) Take a silicon wafer with a thickness of 110 μm and a size of 210×105 mm. After the cleaning process, remove the organic dirt, metal impurities, and surface damage layer on the surface of the silicon wafer; after cleaning, use an alkali solution to texture the silicon wafer to form a textured layer on the front and back sides of the silicon wafer;

[0090] (2) By the PECVD method, deposit an intrinsic amorphous silicon layer with a thickness of 6 nm on the front and back sides of the textured silicon wafer in sequence;

[0091] (3) By the PECVD method, deposit an N-type doped microcrystalline silicon layer with a thickness of 30 nm on the surface of the intrinsic amorphous silicon layer on the front side of the silicon wafer;

[0092] (4) By the PECVD method, deposit a P-type doped microcrystalline silicon layer with a thickness of 40 nm on the surface of the intrinsic amorphous silicon layer on the back side of the silicon wafer;

[0093] (5) Use a PVD device to deposit an ITO transparent conductive layer on the surface of the doped microcrystalline silicon layers on the front and back sides of the silicon wafer; the thickness of the ITO transparent conductive layer on the front side is 60 nm, and the thickness of the ITO transparent conductive layer on the back side is 105 nm;

[0094] (6) The silver paste electrodes were printed on the surface of the front ITO layer and the back ITO transparent conductive layer by screen printing method, dried at low temperature at 150 °C and then sintered at 200 °C to obtain the heterojunction solar cell. The cell pattern adopts the multi-main grid line technology solution, and the number of main grid lines of the cell is 18BB.

[0095] Comparative Example 2 (neither the TiO2 layer nor the SiO2 layer is doped with nitrogen):

[0096] The difference between Comparative Example 2 and Example 1 is that nitrogen is not doped when depositing the TiO2 layer and the SiO2 layer in steps (6) and (7). The specific process is as follows:

[0097] (6) By ALD method, using TiCl4 and H2O as the Ti source and O source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, a TiO2 layer with a thickness of 30 nm was deposited on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters were: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, and nitrogen flow rate of 200 sccm; the growth temperature was 220 °C, and the pressure in the reaction chamber was 5 mbar;

[0098] (7) By PECVD method, a SiO2 layer with a thickness of 60 nm was deposited on the surface of the nitrogen-doped TiO2 layer using SiH4 gas; the deposition temperature was 230 °C, the pressure in the chamber was 20 Pa, and the deposition power was 1000 W;

[0099] The remaining steps are the same as those in Example 1.

[0100] Comparative Example 3 (only the TiO2 layer is not doped with nitrogen):

[0101] The difference between Comparative Example 3 and Example 1 is that nitrogen is not doped when depositing the TiO2 layer in step (6). The specific process is as follows:

[0102] (6) By ALD method, using TiCl4 and H2O as the Ti source and O source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, a TiO2 layer with a thickness of 30 nm was deposited on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters were: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, and nitrogen flow rate of 200 sccm; the growth temperature was 220 °C, and the pressure in the reaction chamber was 5 mbar;

[0103] The remaining steps are the same as those in Example 1.

[0104] Comparative Example 4 (only the SiO2 layer is not doped with nitrogen):

[0105] The difference between Comparative Example 4 and Example 1 is that nitrogen is not doped during the deposition of the SiO2 layer in step (7). The specific process is as follows:

[0106] (7) By PECVD method, a SiO2 layer with a thickness of 60 nm is deposited on the surface of the nitrogen-doped TiO2 layer using SiH4 gas; the temperature during deposition is 230 °C, the chamber pressure is 20 Pa, and the deposition power is 1000 W;

[0107] The remaining steps are the same as those in Example 1.

[0108] Comparative Example 5 (excessive nitrogen doping in the TiO2 layer):

[0109] The difference between Comparative Example 5 and Example 1 is that the method for depositing the nitrogen-doped TiO2 layer in step (6) is as follows: By ALD method, using TiCl4, H2O, and NH3 as the Ti source, O source, and N source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, a nitrogen-doped TiO2 layer with a thickness of 30 nm is deposited on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters are: TiCl4 injection for 7 s, nitrogen purge for 30 s, H2O injection for 10 s, nitrogen purge for 12 s, NH3 injection for 30 s, nitrogen purge for 10 s; the NH3 flow rate is 100 sccm, the nitrogen flow rate is 200 sccm; the growth temperature is 220 °C, and the pressure in the reaction chamber is 5 mbar;

[0110] The remaining steps are the same as those in Example 1.

[0111] Comparative Example 6 (excessive nitrogen doping in the SiO2 layer):

[0112] The difference between Comparative Example 6 and Example 1 is that the method for depositing the nitrogen-doped SiO2 layer in step (7) is as follows: Use SiH4-N2O gas to deposit a nitrogen-doped SiO2 layer with a thickness of 60 nm on the surface of the nitrogen-doped TiO2 layer; the flow ratio of N2O to SiH4 is 4, the temperature is 230 °C, the chamber pressure is 20 Pa, and the deposition power is 1000 W;

[0113] The remaining steps are the same as those in Example 1.

[0114] The performance of the heterojunction solar cells prepared in the above examples and comparative examples was tested, and the results are shown in Table 1.

[0115] Table 1: Performance test results of heterojunction solar cells

[0116]

[0117] As can be seen from Table 1, the heterojunction solar cells prepared by the method of the present invention in Examples 1 to 5 have high photoelectric conversion efficiency, open circuit voltage, short circuit current and fill factor. In Comparative Example 1, the TiO2 / SiO2 layer is not provided, and only a relatively thin ITO single-layer antireflection layer is used. The photoelectric conversion efficiency of the battery is significantly decreased compared with that in Example 1. It shows that the formation of the ITO / TiO2 / SiO2 stacked antireflection film of the present invention can ensure that the properties of the heterojunction solar cell are not affected while reducing the thickness of the ITO layer.

[0118] In Comparative Example 2, nitrogen is not doped in the TiO2 layer and the SiO2 layer, and all the performance of the battery is significantly decreased compared with that in Example 1. In Comparative Example 3, only the SiO2 layer is doped with nitrogen, and the TiO2 layer is not doped with nitrogen; in Comparative Example 4, only the TiO2 layer is doped with nitrogen, and the SiO2 layer is not doped with nitrogen. The battery performance is decreased compared with that in Example 1, but is better than that in Comparative Example 2. It shows that nitrogen doping can assist oxygen elements to optimize the energy band structure and the optical performance of the heterojunction battery.

[0119] In Comparative Example 5, too much nitrogen is doped in the TiO2 layer, and the open circuit voltage of the battery is significantly decreased compared with that in Example 1. In Comparative Example 6, too much nitrogen is doped in the SiO2 layer, and the open circuit voltage and fill factor of the battery are decreased compared with that in Example 1, and the effects of the present invention cannot be achieved. It shows that too much nitrogen doping will affect the electron transport performance and is not conducive to the improvement of the film performance.

[0120] It should be noted that in the description of the present invention, "Example" or "specific example" etc. mean that the specific features, structures, materials or characteristics described in connection with the example are included in at least one example of the present invention. Therefore, although the above has used specific examples to elaborate on the invention, it can be understood that the above examples are for understanding the method and core matters of the present invention and cannot be construed as a limitation of the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above examples within the scope of the present invention without departing from the principles and purposes of the present invention. Any simple modification, equivalent change and modification made to the above examples based on the technical essence of the present invention shall be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a heterojunction solar cell, characterized in that the steps It is as follows: (1) Clean and texture the silicon wafer to form a textured layer on both the front and back sides of the silicon wafer; (2) Deposit an intrinsic amorphous silicon layer and a doped microcrystalline silicon layer on the front and back sides of the textured silicon wafer in sequence; the front side is an N-type doped microcrystalline silicon layer, and the back side is a P-type doped microcrystalline silicon layer; (3) Deposit an ITO transparent conductive layer on the surfaces of the doped microcrystalline silicon layers on the front and back sides of the silicon wafer; (4) By ALD method, using TiCl4, H2O and NH3 as the Ti source, O source and N source respectively, and using nitrogen and argon as the purge gas and carrier gas respectively, deposit a nitrogen-doped TiO2 layer on the surface of the ITO transparent conductive layer on the front side of the silicon wafer; the growth cycle parameters of the nitrogen-doped TiO2 layer are: TiCl4 injection for 5 - 10 s, nitrogen purge for 25 - 35 s, H2O injection for 8 - 14 s, nitrogen purge for 10 - 15 s, NH3 injection for 15 - 25 s, nitrogen purge for 8 - 12 s; the NH3 flow rate is 90 - 110 sccm, the nitrogen flow rate is 180 - 220 sccm; the growth temperature is 210 - 220 °C, and the pressure in the reaction chamber is 4 - 6 mbar; the thickness of the nitrogen-doped TiO2 layer is 25 - 50 nm; (5) By PECVD method, use SiH4-N2O gas to deposit a nitrogen-doped SiO2 layer on the surface of the nitrogen-doped TiO2 layer; the flow rate ratio of N2O and SiH4 is 1 - 3, the temperature is 210 - 230 °C, the pressure in the chamber is 15 - 20 Pa, and the deposition power is 850 - 1000 W; the thickness of the nitrogen-doped SiO2 layer is 50 - 90 nm; (6) Print silver paste electrodes on the surface of the nitrogen-doped SiO2 layer on the front side and the ITO transparent conductive layer on the back side, and obtain the heterojunction solar cell after drying and sintering; The sintering temperature is lower than 300 °C.

2. The preparation method of the heterojunction solar cell according to claim 1, characterized in that, In step (3), the thickness of the front ITO transparent conductive layer is 50 - 80 nm, and the thickness of the back ITO transparent conductive layer is 80 - 140 nm.

3. The method for preparing a heterojunction solar cell according to claim 1 or 2, characterized in that, In step (3), the ITO transparent conductive layer is deposited by PVD or RPD method.

4. The preparation method of the heterojunction solar cell according to claim 1, characterized in that, The thickness of the silicon wafer used in step (1) is 80 - 180 μm.

5. The preparation method of the heterojunction solar cell according to claim 1, characterized in that, The thickness of the intrinsic amorphous silicon layers on the front and back sides of the silicon wafer in step (2) is 3 - 15 nm.

6. The preparation method of the heterojunction solar cell according to claim 1, characterized in that, In step (2), the thickness of the front N-type doped microcrystalline silicon layer is 10 - 40 nm, and the thickness of the back P-type doped microcrystalline silicon layer is 15 - 45 nm.

7. The method for preparing a heterojunction solar cell according to claim 1 or 5 or 6, characterized in that, In step (2), the intrinsic amorphous silicon layer and the doped microcrystalline silicon layer are deposited by PECVD, HWCVD or LPCVD method.

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