A back contact solar cell, a method of manufacturing the same, and a photovoltaic module

Abstract

The application discloses a back contact solar cell, a preparation method thereof and a photovoltaic module, and relates to the technical field of photovoltaics. The application forms a quantum dot layer on both a phosphorus-doped polysilicon layer and a boron-doped polysilicon layer, which, on one hand, widens the light absorption of the cell based on the up-conversion effect of the quantum dots, and on the other hand, makes full use of the quantum dot layer to sufficiently reduce the side wall dangling bonds and make up for the shortcomings of a traditional composite film.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and more specifically, to a back-contact solar cell, its preparation method, and a photovoltaic module. Background Technology

[0002] To maximize sunlight utilization, existing back-contact solar cells typically focus on front-side anti-reflection effects, such as secondary texturing and pyramidal spherical shaping. However, they still cannot fully absorb far-infrared light. On the other hand, back-contact solar cells often focus on front-side passivation and the back-side PN region, neglecting the influence of etched sidewalls. The etched sidewalls on the back of the cell contain a large number of dangling bonds, and traditional composite film deposition methods cannot guarantee complete passivation of the sidewalls. These defects make the sidewalls high-incidence areas for carrier recombination, increasing parasitic absorption.

[0003] Therefore, it is urgent to repair the hanging bonds on the sidewalls of the etched grooves to improve the photoelectric conversion efficiency of the battery.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a back-contact solar cell, its preparation method, and a photovoltaic module, with the aim of improving photoelectric conversion efficiency.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a back-contact solar cell, including a substrate having opposing surfaces and a backlight surface, a first region and a second region that do not contact each other being disposed on the backlight surface, and an isolation groove being disposed between the first region and the second region. A tunneling oxide layer, a phosphorus-doped polycrystalline silicon layer, and a first quantum dot layer are sequentially disposed on a first region of the substrate. A tunneling oxide layer, a boron-doped polycrystalline silicon layer, and a second quantum dot layer are sequentially disposed on the second region of the substrate.

[0007] In an optional implementation, a first quantum dot layer and / or a second quantum dot layer cover the sidewalls and bottom of the isolation trench; And / or, the materials used to form the first quantum dot layer and the second quantum dot layer are independently selected from at least one of carbon quantum dots and nitrogen-doped carbon quantum dots; And / or, the thickness of the first quantum dot layer and the second quantum dot layer is independently 5nm-20nm.

[0008] In an optional embodiment, the thickness of the tunneling oxide layer is 0.4 nm to 1.8 nm; And / or, the doping concentration of the phosphorus-doped polycrystalline silicon layer is 2E-20~5E-20, and the thickness is 150μm-300μm; And / or, the boron-doped polycrystalline silicon layer has a doping concentration of 1E-19 to 5E-19 and a thickness of 220μm to 380μm.

[0009] In an optional embodiment, a first passivation layer and a first antireflection layer are further disposed on the first quantum dot layer; And / or, a second passivation layer and a second antireflection layer are also disposed on the second quantum dot layer; And / or, a third passivation layer and a third antireflection layer are sequentially disposed on the surface of the substrate; And / or, electrodes are provided in both the first and second regions.

[0010] In an optional embodiment, the materials of the first passivation layer, the second passivation layer, and the third passivation layer are all selected from at least one of aluminum oxide and silicon oxide; the thicknesses of the first passivation layer, the second passivation layer, and the third passivation layer are independently 3.5 μm to 5.5 μm; And / or, the materials of the first antireflection layer, the second antireflection layer and the third antireflection layer are all selected from at least one of silicon nitride and silicon oxynitride; the thicknesses of the first antireflection layer, the second antireflection layer and the third antireflection layer are independently 75μm-95μm.

[0011] Secondly, the present invention provides a method for preparing a back-contact solar cell according to any of the foregoing embodiments, comprising: Preparation of intermediates: A first region and a second region that do not contact each other are formed on the back surface of the substrate. A tunneling oxide layer and a phosphorus-doped polycrystalline silicon layer are sequentially disposed on the first region, and a tunneling oxide layer and a boron-doped polycrystalline silicon layer are sequentially disposed on the second region. Quantum dot layer preparation: Quantum dot layers were formed on both phosphorus-doped polycrystalline silicon layers and boron-doped polycrystalline silicon layers.

[0012] In an optional embodiment, quantum dot particles are prepared by a hydrothermal method, and the quantum dot particles and solvent are mixed to obtain a mixture, which is then used to form the quantum dot layer. The steps for preparing quantum dot particles include: mixing quantum dot raw materials and water to obtain a mixed solution, keeping the mixed solution at 180℃-250℃ for 4h-24h, cooling after the reaction is completed, centrifuging to remove large particles with a size >50nm, dialysis to remove small molecules with a size <1nm, and drying after centrifugation or dialysis; the quantum dot raw materials are carbon sources or a mixture of carbon and nitrogen sources; wherein, in the mixture of carbon and nitrogen sources, the mass ratio of carbon source to nitrogen source is 1:(1-3), and the mass ratio of carbon source to water is (0.5-3.0):400.

[0013] In an optional embodiment, the carbon source is selected from at least one of glucose and citric acid; And / or, the nitrogen source is selected from at least one of urea, thiourea and ethylenediamine; And / or, the drying temperature is 100℃-250℃, and the drying time is 12h-36h; And / or, spray or spin coat the mixture onto the intermediate and heat treat it at 80℃-180℃ for 5min-30min; And / or, the solvent is selected from at least one of ethanol and isopropanol; the mass ratio of quantum dot particles to solvent is 1:(500-2000).

[0014] In an optional embodiment, the method further includes: preparing a passivation layer and an antireflection layer on the surfaces of both the quantum dot layer and the substrate, and preparing electrodes on both the first region and the second region.

[0015] Thirdly, the present invention provides a photovoltaic module, including any of the back-contact solar cells in the foregoing embodiments or back-contact solar cells prepared by any of the preparation methods in the foregoing embodiments.

[0016] The present invention has the following beneficial effects: The present invention forms quantum dot layers on both phosphorus-doped polycrystalline silicon layers and boron-doped polycrystalline silicon layers. On the one hand, the upconversion effect of quantum dots broadens the light absorption of the battery. On the other hand, the quantum dot layer can significantly reduce sidewall dangling bonds, thus overcoming the shortcomings of traditional composite films.

[0017] Specifically, when light shines on the front side of a back-contact solar cell, some high-energy particles (such as shorter-wavelength ultraviolet or blue photons) are absorbed by the silicon nitride film. The carbon quantum dots modified on the silicon nitride film possess downconversion luminescence properties and can absorb these high-energy particles. Due to the quantum confinement effect and the effect of surface states, after absorbing high-energy particles, the electrons inside the carbon quantum dots are excited to a higher energy state. Subsequently, during the transition of these electrons from the higher energy state back to the lower energy state, they emit lower-energy particles with longer wavelengths. The wavelengths of these lower-energy particles are within the light transmission range of the silicon nitride film, allowing them to pass through the silicon nitride film and enter the silicon substrate. There, they are absorbed by the silicon substrate and generate photogenerated carriers, thereby enhancing the cell's light absorption and improving the photoelectric conversion efficiency.

[0018] Quantum dot layers prepared by solution method can better fill trenches, reduce dangling bonds on trench sidewalls, and compensate for the shortcomings of traditional composite films in terms of insufficient passivation of trench sidewalls. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A diagram illustrating the intermediate process of fabricating a back-contact solar cell; Figure 2 This is an intermediate product diagram of a back-contact solar cell.

[0021] Icons: 101 - Tunneling oxide layer; 102 - Phosphorus-doped polycrystalline silicon layer; 103 - Boron-doped polycrystalline silicon layer; 104 - Second quantum dot layer; 105 - First quantum dot layer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] like Figure 1 and Figure 2 As shown, Figure 1 This is a diagram of the intermediate process. Figure 2 The diagram shows an intermediate product. This embodiment of the invention provides a back-contact solar cell, including a substrate with opposing surfaces and a backlight surface. A first region and a second region, which are not in contact with each other, are formed on the backlight surface. The first region can be an N-type region, and the second region can be a P-type region. An isolation trench is formed between the first and second regions. A tunneling oxide layer 101, a phosphorus-doped polycrystalline silicon layer 102, and a first quantum dot layer 105 are sequentially formed on the first region of the substrate. A tunneling oxide layer 101, a boron-doped polycrystalline silicon layer 103, and a second quantum dot layer 104 are sequentially formed on the second region of the substrate. The first quantum dot layer and / or the second quantum dot layer cover the sidewalls and bottom of the isolation trench.

[0024] Figure 2 The structure can serve as an intermediate product (when used as an intermediate product, a sealing protective film can be used to protect the quantum dot layer to prevent degradation upon contact with air), upon which a passivation layer and an antireflection layer (such as silicon carbide) can be deposited using conventional processes. The inventors discovered that alumina deposition can only repair dangling bonds in the shallow surface layer and cannot repair residues and microcracks left after laser etching. Carbon quantum dots can convert high-energy particles that might be absorbed by the silicon nitride film into low-energy particles that can pass through the film, allowing more light energy to be utilized by the battery, significantly improving the battery's light absorption efficiency and thus enhancing its photoelectric conversion efficiency. Furthermore, the quantum dot layer can also repair dangling bonds on the sidewalls of the etched grooves; the fabrication process of the quantum dot layer is simple and inexpensive.

[0025] In some embodiments, the materials used to form the first quantum dot layer 105 and the second quantum dot layer 104 are independently selected from at least one of carbon quantum dots and nitrogen-doped carbon quantum dots, and can be any one or both. The thicknesses of the first quantum dot layer and the second quantum dot layer can be the same or different, and can be independently 5nm-20nm, such as 5nm, 8nm, 10nm, 13nm, 15nm, 18nm, 20nm, etc. By controlling the thickness of the quantum dot layer, its upconversion effect can be better utilized to broaden the light absorption of the battery and improve the light absorption efficiency.

[0026] Taking nitrogen-doped carbon quantum dots as an example to illustrate its working principle: Nitrogen-doped carbon quantum dots (N CQDs (Chemical Q-Dip Depositions) leverage their nanoscale effect and solution penetration properties to penetrate microcracks, high aspect ratio trench dead zones, and etching pits left by laser etching through capillary action, overcoming the diffusion limitations of traditional vapor-deposited thin films. Their abundant amino and pyridine nitrogen functional groups can form stable Si with silicon dangling bonds within the cracks. N coordinate bond or Si O covalent bonds enable deep chemical passivation from the surface to the subsurface. Meanwhile, N... CQDs can lightly fill micropores and defect channels, blocking carrier recombination paths. Therefore, in trench sidewalls with laser residual damage and complex microstructures, N CQDs can achieve passivation of dead angles and repair of deep defects that are difficult to cover with ALD ultrathin alumina.

[0027] In some embodiments, the thickness of the tunneling oxide layer is 0.4 nm to 1.8 nm, such as 0.4 nm, 0.6 nm, 0.8 nm, 1.0 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, etc.; the doping concentration of the phosphorus-doped polycrystalline silicon layer is 2E-20 to 5E-20, such as 2E-20, 3E-20, 4E-20, 5E-20, etc.; the thickness of the phosphorus-doped polycrystalline silicon layer is 150 μm to 300 μm, such as 150 μm. The thickness of the boron-doped polycrystalline silicon layer is 1E-19 to 5E-19, such as 1E-19, 2E-19, 3E-19, 4E-19, 5E-19, etc.; the thickness of the boron-doped polycrystalline silicon layer is 220μm-380μm, such as 220μm, 250μm, 280μm, 300μm, 320μm, 350μm, 380μm, etc.

[0028] In some embodiments, a first passivation layer and a first antireflection layer are further disposed on the first quantum dot layer, and a second passivation layer and a second antireflection layer are further disposed on the second quantum dot layer. A third passivation layer and a third antireflection layer are sequentially disposed on the surface (light-facing side) of the substrate. Electrodes are disposed on both the first and second regions, and the material of the electrodes is not limited.

[0029] Furthermore, the materials of the first passivation layer, the second passivation layer, and the third passivation layer are all selected from at least one of alumina and silicon oxide, and the materials of the first passivation layer, the second passivation layer, and the third passivation layer can be any one or more of the above, and can all be alumina. The thickness of the first passivation layer, the second passivation layer, and the third passivation layer is independently 3.5μm-5.5μm, such as 3.5μm, 3.8μm, 4.0μm, 4.3μm, 4.5μm, 4.8μm, 5.0μm, 5.3μm, 5.5μm, etc. By adjusting the material and thickness of the passivation layer, a better passivation effect can be achieved.

[0030] Furthermore, the materials of the first, second, and third antireflective layers are all selected from at least one of silicon nitride and silicon oxynitride. The materials of the first, second, and third antireflective layers can be any one or more of the above, and can all be silicon nitride. The thicknesses of the first, second, and third antireflective layers are independently between 75μm and 95μm, such as 75μm, 80μm, 85μm, 90μm, and 95μm. By adjusting the material and thickness of the antireflective layers, the light energy utilization rate can be further improved.

[0031] This invention provides a method for fabricating a back-contact solar cell, comprising the following steps: S1. Preparation of intermediates A first region and a second region that do not contact each other are formed on the back surface of the substrate. A tunneling oxide layer 101 and a phosphorus-doped polycrystalline silicon layer 102 are sequentially disposed on the first region, and a tunneling oxide layer 101 and a boron-doped polycrystalline silicon layer 103 are sequentially disposed on the second region, forming a structure as shown in the figure. Figure 1 The structure shown.

[0032] The fabrication processes for the tunneling oxide layer 101, the phosphorus-doped polysilicon layer 102, and the boron-doped polysilicon layer 103 are not limited, and the thickness and doping concentration of each layer are as described above. Specifically, after polishing the bare silicon, p-poly and BSG are formed by LPCVD + boron diffusion. The first region of BSG is opened by laser 1, and the p-poly of the first region is removed by wet process, and then n-poly and PSG are formed by LP + phosphorus diffusion. The second region of PSG is opened by laser 2, and the n-poly of the second region is removed by wet process, finally forming the tunneling oxide layer 101, the boron-doped polysilicon layer 103, and the phosphorus-doped polysilicon layer 102.

[0033] S2, Preparation of quantum dot layer Quantum dot layers were formed on both the phosphorus-doped polycrystalline silicon layer 102 and the boron-doped polycrystalline silicon layer 103, resulting in... Figure 2 The structure shown uses quantum dots to modify the etched silicon wafer. Based on the upconversion effect of quantum dots, the light absorption of the battery can be broadened.

[0034] The fabrication process of the quantum dot layer is not limited. For example, quantum dots can be prepared using a sol-gel or hydrothermal method and deposited on the silicon wafer surface using a slow dip-coating method, thereby significantly reducing sidewall dangling bonds. Alternatively, a quantum dot layer can be formed by coating a quantum dot solution and then drying it. In a preferred embodiment, a solution method is used to prepare the quantum dot layer, which covers the sidewalls and bottom of the isolation trench.

[0035] In some embodiments, quantum dot particles are prepared by a hydrothermal method, in which quantum dot particles and a solvent are mixed to obtain a mixture, and the quantum dot layer is formed using the mixture. The specific formation method is not limited.

[0036] Further, the steps for preparing quantum dot particles include: mixing quantum dot raw materials with water to obtain a mixture; maintaining the mixture at 180℃-250℃ for 4h-24h to complete the hydrothermal reaction; cooling after the reaction; centrifuging to remove large particles >50nm; dialysis to remove small molecules <1nm; and drying after centrifugation or dialysis to obtain quantum dot particles with a size of 2nm~10nm. The quantum dot raw materials are carbon sources or mixtures of carbon and nitrogen sources. Carbon quantum dots (CQDs) are prepared using carbon sources, and nitrogen-doped carbon quantum dots are prepared using mixtures of carbon and nitrogen sources. In the mixture of carbon and nitrogen sources, the mass ratio of carbon to nitrogen is 1:(1-3), such as 1:1, 1:2, 1:3, etc.; the mass ratio of carbon to water is (0.5-3.0):400, such as 0.5:400, 1.0:400, 1.5:400, 2.0:400, 2.5:400, 3.0:400, etc. Specifically, the hydrothermal reaction temperature can be 180℃, 200℃, 230℃, 250℃, etc.; the hydrothermal reaction time can be 4h, 8h, 10h, 15h, 20h, 24h, etc.

[0037] Furthermore, the carbon source is selected from at least one of glucose and citric acid, and can be any one or more of the above; the nitrogen source is selected from at least one of urea, thiourea, and ethylenediamine, and can be any one or more of the above. The drying temperature is 100℃-250℃, such as 100℃, 130℃, 150℃, 180℃, 200℃, 230℃, 250℃, etc.; the drying time is 12h-36h, such as 12h, 15h, 18h, 20h, 25h, 30h, 36h, etc. Centrifugation can be performed using a centrifuge, and the centrifugation time can be 10min-40min.

[0038] Furthermore, a quantum dot layer is formed by coating. The obtained mixture of quantum dots (such as CQDs) is sprayed or spin-coated onto an intermediate and then heat-treated at 80℃-180℃ (e.g., 80℃, 100℃, 130℃, 150℃, 180℃, etc.) for 5min-30min (e.g., 5min, 10min, 15min, 20min, 25min, 30min, etc.) to form the quantum dot layer. The solvent is selected from at least one of ethanol and isopropanol, and any one or more of the above solvents can be used; the mass ratio of carbon quantum dot (CQDs) particles to solvent is 1:(500-2000), such as 1:500, 1:800, 1:1000, 1:1300, 1:1500, 1:1800, 1:2000, etc.

[0039] S3. Prepare the complete battery structure A passivation layer and an antireflection layer are fabricated on the surfaces of both the quantum dot layer and the substrate. Electrodes are fabricated on both the first and second regions to form a complete battery structure. The materials and thicknesses of the passivation layer and the antireflection layer are described above.

[0040] This invention also provides a photovoltaic module, which includes the aforementioned solar back contact cell. The performance of the module can be further improved by optimizing the structure of the solar back contact cell.

[0041] Specifically, the photovoltaic module includes multiple strings of cells arranged in a flat manner and an encapsulation layer covering each string of cells, each string of cells including several solar cells connected in series.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1 This embodiment provides a method for fabricating a back-contact solar cell, the steps of which are as follows: (1) Preparation of intermediates Take an n-type silicon wafer with a thickness of 150μm and set it aside.

[0044] The bare silicon is polished, and a tunneling oxide layer and a poly layer are deposited using LPCVD. After boron diffusion, a p-poly layer is formed, followed by the deposition of a BSG layer.

[0045] The process parameters for depositing the tunneling oxide layer are as follows: The tunneling oxide layer is prepared using LPCVD; the preparation process includes: introducing oxygen and nitrogen, and depositing the tunneling oxide layer; the oxygen gas flow rate is 10000 sccm; the nitrogen gas flow rate is 20000 sccm; the deposition temperature is 450℃; and the deposition time is 300 s. The process parameters for depositing the poly layer are as follows: The intrinsic amorphous silicon layer is prepared using LPCVD; the preparation process includes: introducing silane, and depositing the intrinsic amorphous silicon layer; the silane gas flow rate is 1000 sccm; the deposition temperature is 550℃; the deposition time is 2 h; and the working pressure is 300 mTorr. The process parameters for boron diffusion are as follows: BCl3 and O2 are introduced, and the BSG layer is deposited; the BCl3 gas flow rate is 200 sccm; the O2 gas flow rate is 500 sccm; the deposition time is 800 s; and the deposition temperature is 850℃.

[0046] The BSG layer in the first region of the laser-etched film is subjected to wet processing to remove the p-poly layer in the first region, followed by LPCVD deposition of a poly layer. After phosphorus diffusion, an n-poly layer is formed, and then a PSG layer is deposited. The process parameters for depositing the poly layer are as follows: The intrinsic amorphous silicon layer is prepared using LPCVD; the preparation process of the intrinsic amorphous silicon layer includes: introducing silane and depositing the intrinsic amorphous silicon layer; the silane gas flow rate is 1000 sccm; the deposition temperature is 550℃; the deposition time is 2 h; and the working pressure is 300 mTorr. The process parameters for phosphorus diffusion are as follows: phosphorus oxychloride and oxygen are introduced; the phosphorus oxychloride gas flow rate is 800 sccm; the oxygen gas flow rate is 800 sccm; the deposition temperature is 750℃; the deposition time is 1000 s; after deposition, oxygen is introduced for oxidation propulsion; the oxygen gas flow rate for oxidation propulsion is 5000 sccm; the oxidation propulsion temperature is 900℃; and the propulsion time is 1500 s.

[0047] Laser-assisted ablation of the second region's PSG layer, followed by wet removal of the n-poly layer in the second region, ultimately forming a tunneling oxide layer 101, a boron-doped polycrystalline silicon layer 103, and a phosphorus-doped polycrystalline silicon layer 102. Figure 1 As shown. The thickness of the tunneling oxide layer 101 is 1.1 nm, the doping concentration of the phosphorus-doped polysilicon layer is 3E-20 and the thickness is 220 nm, and the doping concentration of the boron-doped polysilicon layer is 2E-19 and the thickness is 300 nm.

[0048] (2) Preparation of quantum dot layer 1.5g of glucose was dissolved in 400g of water, and 3g of urea was used as the nitrogen source. After stirring magnetically until homogeneous, the mixture was placed in a reaction vessel for hydrothermal treatment at 200℃ for 12h to obtain a nitrogen-doped carbon quantum dot (NCQD) solution. This solution was purified by centrifugation and dialysis to remove large particles and small molecules. After centrifugation for 30min, the final nitrogen-doped carbon quantum dot (NCQD) solution was obtained. After drying at 150℃ for 24h, nitrogen-doped carbon quantum dots (NCQDs) were obtained.

[0049] Nitrogen-doped carbon quantum dot (NCQD) particles and ethanol were mixed at a mass ratio of 1:1000 to obtain a mixture. The mixture was sprayed onto a boron-doped polycrystalline silicon layer 103 and a phosphorus-doped polycrystalline silicon layer 102, and then heat-treated at 130°C for 20 min to obtain a quantum dot layer with a thickness of 10 nm, namely the first quantum dot layer 105 and the second quantum dot layer 104.

[0050] (3) Fabrication of complete battery structure Passivation layers and antireflection layers were fabricated on the surfaces of both the quantum dot layer and the substrate. The passivation layers were all made of aluminum oxide and had a thickness of 4.5 nm. The antireflection layers were all made of silicon nitride and had a thickness of 85 nm.

[0051] Silver electrodes were fabricated in both the first and second regions to form a complete battery structure.

[0052] Example 2 This embodiment provides a method for fabricating a back-contact solar cell, the steps of which are as follows: (1) Preparation of intermediates Take an n-type silicon wafer with a thickness of 150μm and set it aside.

[0053] The bare silicon was polished, and a tunneling oxide layer and a poly layer were deposited using LPCVD. After boron diffusion, p-poly was formed, followed by the deposition of a BSG layer. The main difference from Example 1 is that the thickness of the tunneling oxide layer 101 is 0.4 nm, the doping concentration of the phosphorus-doped polysilicon layer is 2E-20 and the thickness is 150 nm, and the doping concentration of the boron-doped polysilicon layer is 1E-19 and the thickness is 220 nm.

[0054] (2) Preparation of quantum dot layer 0.5g of glucose was dissolved in 400g of water, and 0.5g of urea was used as a nitrogen source. After being magnetically stirred evenly, the mixture was placed in a reaction vessel for hydrothermal treatment at 180℃ for 24h to obtain a nitrogen-doped carbon quantum dot (NCQD) solution. This solution was purified by centrifugation and dialysis to remove large particles and small molecules. After centrifugation for 30min, the final nitrogen-doped carbon quantum dot (NCQD) solution was obtained. After drying at 100℃ for 36h, nitrogen-doped carbon quantum dots (NCQDs) were obtained.

[0055] Nitrogen-doped carbon quantum dot (NCQD) particles and ethanol were mixed at a mass ratio of 1:500 to obtain a mixture. The mixture was sprayed onto a boron-doped polycrystalline silicon layer 103 and a phosphorus-doped polycrystalline silicon layer 102, and then heat-treated at 80°C for 30 min to obtain a quantum dot layer with a thickness of 5 nm, namely the first quantum dot layer 105 and the second quantum dot layer 104.

[0056] (3) Fabrication of complete battery structure Passivation layers and antireflection layers were fabricated on the surfaces of both the quantum dot layer and the substrate. The passivation layers were all made of aluminum oxide and had a thickness of 3.5 nm. The antireflection layers were all made of silicon nitride and had a thickness of 75 nm.

[0057] Silver electrodes were fabricated in both the first and second regions to form a complete battery structure.

[0058] Example 3 This embodiment provides a method for fabricating a back-contact solar cell, the steps of which are as follows: (1) Preparation of intermediates Take an n-type silicon wafer with a thickness of 150μm and set it aside.

[0059] The bare silicon was polished, and a tunneling oxide layer and a poly layer were deposited using LPCVD. After boron diffusion, p-poly was formed, followed by the deposition of a BSG layer. The main difference from Example 1 is that the thickness of the tunneling oxide layer 101 is 1.8 nm, the doping concentration of the phosphorus-doped polysilicon layer is 5E-20 and the thickness is 300 nm, and the doping concentration of the boron-doped polysilicon layer is 5E-19 and the thickness is 380 nm.

[0060] (2) Preparation of quantum dot layer 3.0g of glucose was dissolved in 400g of water, and 9g of urea was used as the nitrogen source. After being magnetically stirred evenly, the mixture was placed in a reaction vessel for hydrothermal treatment at 250℃ for 4 hours to obtain a nitrogen-doped carbon quantum dot (NCQD) solution. This solution was purified by centrifugation and dialysis to remove large particles and small molecules. After centrifugation for 30 minutes, the final nitrogen-doped carbon quantum dot (NCQD) solution was obtained. After drying at 250℃ for 12 hours, nitrogen-doped carbon quantum dots (NCQDs) were obtained.

[0061] Nitrogen-doped carbon quantum dot (NCQD) particles and ethanol were mixed at a mass ratio of 1:2000 to obtain a mixture. This mixture was then sprayed onto a boron-doped polycrystalline silicon layer 103 and a phosphorus-doped polycrystalline silicon layer 102, and heat-treated at 180°C for 5 minutes to obtain a quantum dot layer with a thickness of 5 nm, namely the first quantum dot layer 105 and the second quantum dot layer 104.

[0062] (3) Fabrication of complete battery structure Passivation layers and antireflection layers were fabricated on the surfaces of both the quantum dot layer and the substrate. The passivation layers were all made of aluminum oxide and had a thickness of 5.5 nm. The antireflection layers were all made of silicon nitride and had a thickness of 95 nm.

[0063] Silver electrodes were fabricated in both the first and second regions to form a complete battery structure.

[0064] Example 4 The only difference from Example 1 is step (2), which is as follows: 3g of glucose was dissolved in 400g of water, and 6g of urea was used as the nitrogen source. After being magnetically stirred evenly, the mixture was placed in a reaction vessel for hydrothermal treatment at 200℃ for 12h to obtain a nitrogen-doped carbon quantum dot (NCQD) solution. This solution was purified by centrifugation and dialysis to remove large particles and small molecules. After centrifugation for 30min, the final nitrogen-doped carbon quantum dot (NCQD) solution was obtained. After drying at 150℃ for 24h, nitrogen-doped carbon quantum dots (NCQDs) were obtained.

[0065] Nitrogen-doped carbon quantum dot (NCQD) particles and ethanol were mixed at a mass ratio of 1:1000 to obtain a mixture. The mixture was sprayed onto a boron-doped polycrystalline silicon layer 103 and a phosphorus-doped polycrystalline silicon layer 102, and then heat-treated at 130°C for 20 min to obtain a quantum dot layer with a thickness of 10 nm, namely the first quantum dot layer 105 and the second quantum dot layer 104.

[0066] Example 5 The only difference from Example 1 is step (2), which is as follows: 0.5g of glucose was dissolved in 400g of water, and 1g of urea was used as the nitrogen source. After stirring magnetically until homogeneous, the mixture was placed in a reaction vessel for hydrothermal treatment at 200℃ for 12h to obtain a nitrogen-doped carbon quantum dot (NCQD) solution. This solution was purified by centrifugation and dialysis to remove large particles and small molecules. After centrifugation for 30min, the final nitrogen-doped carbon quantum dot (NCQD) solution was obtained. After drying at 150℃ for 24h, nitrogen-doped carbon quantum dots (NCQDs) were obtained.

[0067] Nitrogen-doped carbon quantum dot (NCQD) particles and ethanol were mixed at a mass ratio of 1:1000 to obtain a mixture. The mixture was sprayed onto a boron-doped polycrystalline silicon layer 103 and a phosphorus-doped polycrystalline silicon layer 102, and then heat-treated at 130°C for 20 min to obtain a quantum dot layer with a thickness of 10 nm, namely the first quantum dot layer 105 and the second quantum dot layer 104.

[0068] Example 6 The only difference from Example 1 is that the thickness of the quantum dot layer is 5 nm.

[0069] Example 7 The only difference from Example 1 is that the thickness of the quantum dot layer is 25 nm.

[0070] Example 8 The only difference from Example 1 is that no nitrogen source is added, and pure carbon quantum dots (CQDs) are prepared.

[0071] Example 9 The only difference from Example 1 is that in step (2), the mass ratio of nitrogen-doped carbon quantum dot (NCQD) particles to ethanol is 1:2000.

[0072] Example 10 The only difference from Example 1 is that in step (2), the mass ratio of nitrogen-doped carbon quantum dot (NCQD) particles to ethanol is 1:500.

[0073] Comparative Example 1 The only difference from Example 1 is that step (2) is not performed.

[0074] Experimental Example 1 The performance of the back-contact solar cells prepared in the examples and comparative examples was tested using conventional IV testing methods, and the results are shown in Table 1.

[0075] Table 1. Performance of the back-contact solar cells prepared in the examples and comparative examples.

[0076] As can be seen from Table 1, the present invention uses quantum dot modification to etch silicon wafers, which can improve battery performance.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A back-contact solar cell, characterized in that, Includes a substrate having opposing surfaces and a backlight surface, wherein a first region and a second region that do not contact each other are provided on the backlight surface, and an isolation groove is provided between the first region and the second region; A tunneling oxide layer, a phosphorus-doped polycrystalline silicon layer, and a first quantum dot layer are sequentially disposed on a first region of the substrate; A tunneling oxide layer, a boron-doped polycrystalline silicon layer, and a second quantum dot layer are sequentially disposed on the second region of the substrate.

2. The back-contact solar cell according to claim 1, characterized in that, The first quantum dot layer and / or the second quantum dot layer cover the sidewalls and bottom of the isolation trench; And / or, the materials used to form the first quantum dot layer and the second quantum dot layer are independently selected from at least one of carbon quantum dots and nitrogen-doped carbon quantum dots; And / or, the thicknesses of the first quantum dot layer and the second quantum dot layer are independently 5nm-20nm.

3. The back-contact solar cell according to claim 1, characterized in that, The thickness of the tunneling oxide layer is 0.4 nm to 1.8 nm; And / or, the doping concentration of the phosphorus-doped polycrystalline silicon layer is 2E-20~5E-20, and the thickness is 150μm-300μm; And / or, the boron-doped polycrystalline silicon layer has a doping concentration of 1E-19 to 5E-19 and a thickness of 220μm to 380μm.

4. The back-contact solar cell according to claim 1, characterized in that, A first passivation layer and a first antireflection layer are also disposed on the first quantum dot layer; And / or, a second passivation layer and a second antireflection layer are further disposed on the second quantum dot layer; And / or, a third passivation layer and a third antireflection layer are sequentially disposed on the surface of the substrate; And / or, electrodes are provided in both the first region and the second region.

5. The back-contact solar cell according to claim 4, characterized in that, The materials of the first passivation layer, the second passivation layer, and the third passivation layer are all selected from at least one of aluminum oxide and silicon oxide; the thicknesses of the first passivation layer, the second passivation layer, and the third passivation layer are independently 3.5 μm-5.5 μm; And / or, the materials of the first antireflection layer, the second antireflection layer and the third antireflection layer are all selected from at least one of silicon nitride and silicon oxynitride; the thicknesses of the first antireflection layer, the second antireflection layer and the third antireflection layer are independently 75μm-95μm.

6. A method for preparing a back-contact solar cell according to any one of claims 1-5, characterized in that, include: Preparation of intermediates: A first region and a second region that do not contact each other are formed on the back surface of the substrate. A tunneling oxide layer and a phosphorus-doped polycrystalline silicon layer are sequentially disposed on the first region, and a tunneling oxide layer and a boron-doped polycrystalline silicon layer are sequentially disposed on the second region. Quantum dot layer preparation: Quantum dot layers are formed on both the phosphorus-doped polycrystalline silicon layer and the boron-doped polycrystalline silicon layer.

7. The preparation method according to claim 6, characterized in that, Quantum dot particles are prepared by a hydrothermal method, and the quantum dot particles are mixed with a solvent to obtain a mixture, which is then used to form the quantum dot layer. The steps for preparing the quantum dot particles include: mixing quantum dot raw materials and water to obtain a mixture, keeping the mixture at 180℃-250℃ for 4h-24h, cooling after the reaction, centrifuging to remove large particles >50nm, dialysis to remove small molecules <1nm, and drying after centrifugation or dialysis; the quantum dot raw materials are carbon sources or a mixture of carbon and nitrogen sources; wherein, in the mixture of carbon and nitrogen sources, the mass ratio of the carbon source to the nitrogen source is 1:(1-3), and the mass ratio of the carbon source to water is (0.5-3.0):

400.

8. The preparation method according to claim 7, characterized in that, The carbon source is selected from at least one of glucose and citric acid; And / or, the nitrogen source is selected from at least one of urea, thiourea and ethylenediamine; And / or, the drying temperature is 100℃-250℃, and the drying time is 12h-36h; And / or, the mixture is sprayed or spin-coated onto the intermediate and heat-treated at 80°C-180°C for 5 min-30 min; And / or, the solvent is selected from at least one of ethanol and isopropanol; the mass ratio of the quantum dot particles to the solvent is 1:(500-2000).

9. The preparation method according to claim 6, characterized in that, Also includes: A passivation layer and an antireflection layer are prepared on the surfaces of both the quantum dot layer and the substrate, and electrodes are prepared on both the first region and the second region.

10. A photovoltaic module, characterized in that, This includes the back-contact solar cell according to any one of claims 1-5 or the back-contact solar cell prepared by the preparation method according to any one of claims 6-9.

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