Back contact solar cell, preparation method thereof and photovoltaic module

Abstract

The invention provides a back contact solar cell, a preparation method thereof and a photovoltaic module. The back contact solar cell includes; the N region and the P region are arranged on the backlight surface of the silicon substrate; the isolation region is positioned between the N region and the P region; the P region comprises a first tunneling layer and a p-type doped polycrystalline silicon layer, and the N region comprises a second tunneling layer and an n-type doped polycrystalline silicon layer; the first heat conduction and electric conduction layer is arranged on at least part of the surface, far away from the silicon substrate, of the p-type doped polycrystalline silicon layer or located on the side wall, close to the isolation area, of the p-type doped polycrystalline silicon layer, and the second heat conduction and electric conduction layer is arranged on the side wall of the p-type doped polycrystalline silicon layer. The second heat conduction and electric conduction layer is arranged on at least part of the surface, away from the silicon substrate, of the n-type doped polycrystalline silicon layer or located on the side wall, close to the isolation area, of the n-type doped polycrystalline silicon layer. The back contact solar cell with the structure has better cell performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular, to a back contact solar cell, a preparation method thereof and a photovoltaic module. BACKGROUND

[0002] The emitter of a conventional back contact cell is on the back, and a silicon substrate with high life is required for application, the carriers are separated in the silicon substrate, and then the collection of carriers with different properties is performed on the back of the cell to form effective current transmission. The front of the cell is designed without a gate line, which can maximize the reception of sunlight. At present, the P region and the N region of a full back contact solar cell are separated by a physical isolation method to reduce the recombination of the electron hole in the horizontal transmission process. This structure can better improve the performance of the cell, but there is a reliability problem.

[0003] In the actual scene application process, similar bird droppings, fallen leaves and other obstructions may fall directly above the cell. After the cell is shaded, the cell is affected by the reverse bias, and gradually generates extremely high temperature, which leads to a decrease in efficiency and a shortening of life. In the most serious case, the cell may be burned out. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art. To this end, one object of the present application is to propose a back contact solar cell which can inhibit the accumulation of heat under shading, or improve the heat dissipation efficiency and reduce the local thermal stress.

[0005] In one aspect of the present application, the present application provides a back contact solar cell. According to an embodiment of the present application, the back contact solar cell comprises: a silicon substrate, an N region, a P region and an isolation region between the N region and the P region on a back surface of the silicon substrate, the P region comprising a first tunneling layer, a p-type doped polysilicon layer, the N region comprising a second tunneling layer, an n-type doped polysilicon layer, wherein the first tunneling layer is disposed on a surface of the P region, the second tunneling layer is disposed on a surface of the N region; the p-type doped polysilicon layer is disposed on a side of the first tunneling layer away from the silicon substrate, the n-type doped polysilicon layer is disposed on a side of the second tunneling layer away from the silicon substrate; the back contact solar cell further comprises a thermally and electrically conductive layer of p-type material, the thermally and electrically conductive layer comprising a first thermally and electrically conductive layer and / or a second thermally and electrically conductive layer, the first thermally and electrically conductive layer being disposed on at least part of a surface of the p-type doped polysilicon layer away from the silicon substrate or being located on a side wall of the p-type doped polysilicon layer close to the isolation region, the second thermally and electrically conductive layer being disposed on at least part of a surface of the n-type doped polysilicon layer away from the silicon substrate or being located on a side wall of the n-type doped polysilicon layer close to the isolation region. Thus, the thermally and electrically conductive layer has certain thermal conductivity and electrical conductivity and does not affect the transport of charge carriers, wherein the first thermally and electrically conductive layer forms a P+-P junction structure with the silicon material of the p-type doped polysilicon layer, has a certain "pumping" hole effect, can accelerate the separation and transport of charge carriers, and improves the performance of the solar cell; the second thermally and electrically conductive layer can form an effective built-in PN-like junction structure with the n-type doped polysilicon layer, suppresses the heat accumulation of the solar cell under shading, and at the same time, under the action of high thermal conductivity, can realize rapid and effective heat dissipation, reduces local thermal stress, and protects the use of the solar cell.

[0006] According to an embodiment of the present application, the first thermally and electrically conductive layer extends from the P region to the isolation region.

[0007] According to an embodiment of the present application, the second thermally and electrically conductive layer extends from the N region to the isolation region.

[0008] According to an embodiment of the present application, the thickness of the thermally and electrically conductive layer is 5-10 nm.

[0009] According to an embodiment of the present application, the material of the thermally and electrically conductive layer comprises at least one of graphene and carbon nanotubes.

[0010] In another aspect of the present application, the present application provides a method for preparing the back contact solar cell as described above. According to an embodiment of the present application, the method for preparing the back contact solar cell comprises: sequentially forming a first tunneling layer and a p-type doped polysilicon layer on a P region of a silicon substrate; sequentially forming a second tunneling layer and an n-type doped polysilicon layer on an N region of the silicon substrate; forming a first conductive and heat-conductive layer on a surface of the p-type doped polysilicon layer or on a side wall of the p-type doped polysilicon layer close to the isolation region, and / or forming a second conductive and heat-conductive layer on a surface of the n-type doped polysilicon layer or on a side wall of the n-type doped polysilicon layer close to the isolation region. Thus, the conductive and heat-conductive layer has certain heat conductivity and electrical conductivity, and does not affect the transport of carriers, wherein the first conductive and heat-conductive layer forms a P+-P junction structure with the silicon material of the p-type doped polysilicon layer, has a certain "pumping" hole effect, can accelerate the transport of carriers, and improves the performance of the solar cell; the second conductive and heat-conductive layer can form an effective built-in PN-like junction structure with the n-type doped polysilicon layer, suppresses the heat accumulation of the solar cell under shading, and at the same time, under the action of high heat conductivity, can realize rapid and effective heat dissipation, reduces local thermal stress, and protects the use of the solar cell.

[0011] According to an embodiment of the present application, the method for forming the first conductive and heat-conductive layer and / or the second conductive and heat-conductive layer comprises: forming a layer catalyst film on the surface of the p-type doped polysilicon layer, the n-type doped polysilicon layer, and the silicon substrate of the isolation region; depositing a heat-conductive and conductive material layer on the surface of the catalyst film; and patterning the heat-conductive and conductive material layer to obtain the first conductive and heat-conductive layer and / or the second conductive and heat-conductive layer.

[0012] According to an embodiment of the present application, the material of the catalyst film comprises iron nitrate.

[0013] According to an embodiment of the present application, the heat-conductive and conductive material layer is a carbon nanotube, and the deposition conditions comprise: being performed in an atmosphere containing hydrogen and argon; a deposition temperature of 600-900 ℃; a flow rate of H2 of 10-50 sccm, a flow rate of Ar of 30-120 sccm, and a flow rate of CH4 of 5-30 sccm; and a deposition time of 10-30 minutes.

[0014] In still another aspect of the present application, the present application provides a photovoltaic module. According to an embodiment of the present application, the photovoltaic module comprises the back contact solar cell as described above, or comprises the back contact solar cell prepared by the method as described above. Thus, the photovoltaic module has good heat dissipation efficiency and better cell performance. Those skilled in the art can understand that the photovoltaic module has all the features and advantages of the back contact solar cell as described above, and will not be described in detail here.

[0015] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the attendant drawings or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0016] The foregoing and / or additional aspects and advantages of the present application are achieved by providing a back contact solar cell, comprising a substrate, a back contact layer, a front contact layer, and a plurality of solar cells.

[0017] Figure 1 is a schematic diagram of a partial structure of a back contact solar cell in one embodiment of the present application;

[0018] Figure 2 is a schematic diagram of a partial structure of a back contact solar cell in another embodiment of the present application;

[0019] Figure 3 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0020] Figure 4 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0021] Figure 5 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0022] Figure 6 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0023] Figure 7 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0024] Figure 8 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0025] Figure 9 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0026] Figure 10 is a schematic diagram of a partial structure of a back contact solar cell in yet another embodiment of the present application;

[0027] Figure 11 is a schematic diagram of a structure of a back contact solar cell in yet another embodiment of the present application;

[0028] Figure 12 is a schematic diagram of a structure of a back contact solar cell in yet another embodiment of the present application. DETAILED DESCRIPTION

[0029] The application will be described below with reference to the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the application, and should not be regarded as limiting the scope of the application. If the specific technology or condition is not indicated in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not indicated, it is a conventional product that can be obtained by purchase.

[0030] The application will be described below with reference to the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the application, and should not be regarded as limiting the scope of the application. If the specific technology or condition is not indicated in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not indicated, it is a conventional product that can be obtained by purchase.

[0031] In one aspect of the application, the application provides a back contact solar cell. According to embodiments of the application, with reference to Figures 1 to 8 , the back contact solar cell comprises: a silicon substrate 10, an N region, a P region and an isolation region between the N region and the P region on the back surface of the silicon substrate 10, the P region comprising a first tunneling layer 21, a p-type doped polysilicon layer 31, the N region comprising a second tunneling layer 22, an n-type doped polysilicon layer 32, wherein the first tunneling layer 21 is disposed on the surface of the P region, and the second tunneling layer 22 is disposed on the surface of the N region; the p-type doped polysilicon layer 31 and the n-type doped polysilicon layer 32, the p-type doped polysilicon layer 31 is disposed on the side of the first tunneling layer 32 away from the silicon substrate 10, and the n-type doped polysilicon layer 32 is disposed on the side of the second tunneling layer 22 away from the silicon substrate 10. Further, the solar cell further comprises a thermally and electrically conductive layer 40 of p-type material, the thermally and electrically conductive layer 40 comprising a first thermally and electrically conductive layer 41 and / or a second thermally and electrically conductive layer 42, wherein the setting position of the first thermally and electrically conductive layer 41 and / or the second thermally and electrically conductive layer 42 can include the following cases:

[0032] In some embodiments, with reference to Figure 1 , the thermally and electrically conductive layer 40 only comprises the first thermally and electrically conductive layer 41, and the first thermally and electrically conductive layer 41 is disposed on the surface of the p-type doped polysilicon layer 31 away from the silicon substrate 10. Wherein, the first thermally and electrically conductive layer 41 can be disposed on part or the entire surface of the p-type doped polysilicon layer 31 away from the silicon substrate 10.

[0033] In other embodiments, with reference to Figure 2 , the thermally and electrically conductive layer 40 only comprises the first thermally and electrically conductive layer 41, and the first thermally and electrically conductive layer 41 is located on the side wall of the p-type doped polysilicon layer 31 close to the isolation region. Wherein, the first thermally and electrically conductive layer 41 can cover part or the entire side wall of the p-type doped polysilicon layer 31 close to the isolation region.

[0034] In yet other embodiments, with reference to Figure 3, the heat-conducting and electricity-conducting layer 40 only includes the second heat-conducting and electricity-conducting layer 42, which is arranged on the surface of the n-type doped polysilicon layer 32 away from the silicon substrate 10. In this case, the second heat-conducting and electricity-conducting layer 42 can be arranged on part or the whole surface of the n-type doped polysilicon layer 32 away from the silicon substrate 10.

[0035] In yet some embodiments, referring to Figure 4 , the heat-conducting and electricity-conducting layer 40 only includes the second heat-conducting and electricity-conducting layer 42, which is arranged on the sidewall of the n-type doped polysilicon layer 32 close to the isolation region. In this case, the second heat-conducting and electricity-conducting layer 42 can cover part or the whole sidewall of the n-type doped polysilicon layer 32 close to the isolation region.

[0036] In yet some embodiments, referring to Figures 5 to 8 , the heat-conducting and electricity-conducting layer 40 includes the first heat-conducting and electricity-conducting layer 41 and the second heat-conducting and electricity-conducting layer 42 arranged at intervals, and the first heat-conducting and electricity-conducting layer 41 and the second heat-conducting and electricity-conducting layer 42 can be any combination of the above arrangement cases, such as referring to Figure 5 , the first heat-conducting and electricity-conducting layer 41 is arranged on the surface of the p-type doped polysilicon layer 31 away from the silicon substrate 10, and the second heat-conducting and electricity-conducting layer 42 is arranged on the surface of the n-type doped polysilicon layer 32 away from the silicon substrate 10; or referring to Figure 6 , the first heat-conducting and electricity-conducting layer 41 is arranged on the surface of the p-type doped polysilicon layer 31 away from the silicon substrate 10, and the second heat-conducting and electricity-conducting layer 42 is arranged on the sidewall of the n-type doped polysilicon layer 32 close to the isolation region; or referring to Figure 7 , the first heat-conducting and electricity-conducting layer 41 is arranged on the sidewall of the p-type doped polysilicon layer 31 close to the isolation region, and the second heat-conducting and electricity-conducting layer 42 is arranged on the surface of the n-type doped polysilicon layer 32 away from the silicon substrate 10; or referring to Figure 8 , the first heat-conducting and electricity-conducting layer 41 is arranged on the sidewall of the p-type doped polysilicon layer 31 close to the isolation region, and the second heat-conducting and electricity-conducting layer 42 is arranged on the sidewall of the n-type doped polysilicon layer 32 close to the isolation region.

[0037] According to the embodiments of the present application, the above heat-conducting and electricity-conducting layer has certain heat-conducting and electricity-conducting properties, and does not affect the transmission of carriers, wherein the first heat-conducting and electricity-conducting layer forms a P+-P junction structure with the silicon material of the p-type doped polysilicon layer, has a certain "pumping" hole effect, can accelerate the separation and transmission of carriers, and improves the performance of the solar cell; the second heat-conducting and electricity-conducting layer can form an effective built-in PN-like junction structure with the n-type doped polysilicon layer, suppresses the heat accumulation of the solar cell under shading, and at the same time, under the action of high heat conduction, can realize rapid and effective heat dissipation, reduces local thermal stress, and protects the use of the solar cell.

[0038] According to some embodiments of the present application, referring to Figure 9The first heat-conducting and conductive layer 41 extends from the P region to the isolation region, that is, the distribution of the first heat-conducting and conductive layer 41 extends from the surface of the p-type doped polysilicon layer 31 to the partial surface of the silicon substrate 10 in the isolation region, so that the first heat-conducting and conductive layer 41 covers at least part of the surface of the p-type doped polysilicon layer 31 and also covers the sidewall of the p-type doped polysilicon layer 31 close to the isolation region. Thus, the first heat-conducting and conductive layer of the above structure forms a P+-P junction structure with the silicon material of the p-type doped polysilicon layer, has a certain "pumping" hole effect, can accelerate the separation and transmission of carriers, and improves the performance of the solar cell.

[0039] According to some embodiments of the present application, referring to Figure 10 The second heat-conducting and conductive layer 42 extends from the N region to the isolation region, that is, the distribution of the second heat-conducting and conductive layer 42 extends from the surface of the n-type doped polysilicon layer 32 to the partial surface of the silicon substrate 10 in the isolation region, so that the second heat-conducting and conductive layer 42 covers at least part of the surface of the n-type doped polysilicon layer 32 and also covers the sidewall of the n-type doped polysilicon layer 32 close to the isolation region. The second heat-conducting and conductive layer and the n-type doped polysilicon layer can form an effective built-in PN-like junction structure, inhibit the heat accumulation of the solar cell under shading, and at the same time, under the action of high heat conductivity, can realize rapid and effective heat dissipation, reduce local thermal stress, and protect the use of the solar cell.

[0040] According to some embodiments of the present application, the thickness of the heat-conducting and conductive layer is 5-10 nm, such as 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc. The heat-conducting and conductive layer with the above thickness is convenient to prepare and has uniform thickness, and can play a good heat-conducting and conductive role.

[0041] According to some embodiments of the present application, the material of the heat-conducting and conductive layer includes at least one of graphene and carbon nanotubes. Thus, the heat-conducting and conductive layer with the above material has good heat conductivity and conductivity. In some embodiments, the material of the heat-conducting and conductive layer is graphene; in other embodiments, the material of the heat-conducting and conductive layer is carbon nanotubes (CNT); in still other embodiments, the material of the heat-conducting and conductive layer includes both graphene and carbon nanotubes, and the proportion of the two is not specially required, and those skilled in the art can flexibly design according to the actual situation, which is not limited here.

[0042] According to some embodiments of the present application, the above silicon substrate can be an N-type silicon wafer or a P-type silicon wafer.

[0043] According to some embodiments of the present application, referring to Figure 11The back contact solar cell further comprises: a first passivation layer 51 and a second passivation layer 52, the first passivation layer 51 is arranged on the surface of the light-receiving side of the silicon substrate, and the second passivation layer 52 is arranged on the surface of the isolation region, the p-type doped polysilicon layer 31, the n-type doped polysilicon layer 32 and the thermally conductive and conductive layer 40 of the back light side; a first anti-reflection layer 61 and a second anti-reflection layer 62, the first anti-reflection layer 61 is arranged on the surface of the first passivation layer 51 away from the silicon substrate, and the second anti-reflection layer 62 is arranged on the surface of the second passivation layer 52 away from the silicon substrate; a first electrode 71 and a second electrode 72 on the back light side, the first electrode 71 is in contact with the p-type doped polysilicon layer 31, and the second electrode 72 is in contact with the n-type doped polysilicon layer 32.

[0044] In some embodiments of the present application, the material of the first passivation layer and the second passivation layer comprises but is not limited to aluminum oxide; in some embodiments, the material of the first anti-reflection layer and the second anti-reflection layer respectively comprises but is not limited to at least one of silicon nitride, silicon oxide and silicon oxynitride, and the first anti-reflection layer and the second anti-reflection layer can be a single-layer structure or a multi-layer stacked structure respectively; the material of the first electrode and the second electrode can respectively comprise but is not limited to at least one of copper, aluminum and silver.

[0045] In another aspect of the present application, the present application provides a method for preparing the back contact solar cell described above. According to the embodiments of the present application, referring to Figure 12 The method for preparing the back contact solar cell comprises:

[0046] S100: sequentially forming a first tunneling layer 21 and a p-type doped polysilicon layer 31 on the P region of the silicon substrate 10.

[0047] In some embodiments of the present application, the silicon substrate is subjected to polishing treatment in advance, specifically, the N-type silicon substrate can be subjected to double-side polishing treatment in an alkali polishing tank type machine of a wet process to remove surface dirt, damage and the like.

[0048] In some embodiments of the present application, the first tunneling layer and the p-type doped polysilicon layer can be deposited by using a low pressure chemical vapor deposition method (LPCVD), specifically:

[0049] S110: depositing the first tunneling layer on the back light side of the silicon substrate by using the LPCVD method, the deposition temperature can be 570-650 ℃, and the thickness of the first tunneling layer is 2±0.4 nm;

[0050] S120: depositing the first polysilicon layer on the surface of the first tunneling layer by using the LPCVD method, the thickness of the first polysilicon layer is 290±50 nm, and the deposition temperature is 570-620 ℃;

[0051] S130: p-type ion diffusion is performed on the first polysilicon layer, taking boron diffusion as an example, BCl3 is used as a boron source, boron deposition and diffusion are performed at 900-1000 DEG C to form a p-type doped polysilicon layer, and then boron-silicon glass (BSG) is formed, the thickness of the BSG is 55±5 nm;

[0052] S140: laser is used to perform patterning on the BSG corresponding to the N region and the isolation region of the back light surface, and then hydrofluoric acid solution is used to remove the BSG irradiated by the laser. The power of the laser can be 35-50 W, and the laser can be a green picosecond laser;

[0053] S150: alkali solution (such as sodium hydroxide or potassium hydroxide solution) is used to remove the p-type doped polysilicon layer part and the first tunneling layer part corresponding to the N region and the isolation region, and only the first tunneling layer 21 and the p-type doped polysilicon layer 31 corresponding to the P region are reserved.

[0054] S200: a second tunneling layer 22 and an n-type doped polysilicon layer 32 are sequentially formed in the N region of the silicon substrate 10.

[0055] In some embodiments of the present application, low pressure chemical vapor deposition (LPCVD) can be used to deposit the second tunneling layer and the n-type doped polysilicon layer, specifically:

[0056] S210: the second tunneling layer is deposited on the back light surface of the silicon substrate by using the LPCVD method, the deposition temperature can be 570-650 DEG C, and the thickness of the second tunneling layer is 1.90±0.3 nm;

[0057] S220: the second polysilicon layer is deposited on the surface of the second tunneling layer by using the LPCVD method, the thickness of the second polysilicon layer is 250±30 nm, and the deposition temperature is 590-620 DEG C;

[0058] S230: n-type ion diffusion is performed on the second polysilicon layer, taking phosphorus diffusion as an example, PCl3 is used as a boron source, boron deposition and diffusion are performed to form an n-type doped polysilicon layer, and then phosphorus-silicon glass (PSG) is formed, the thickness of the PSG is 50±5 nm;

[0059] S240: laser is used to perform patterning on the PSG corresponding to the P region and the isolation region of the back light surface, and then hydrofluoric acid solution is used to remove the PSG irradiated by the laser. The power of the laser can be 25-45 W, and the laser can be a green picosecond laser;

[0060] S250: removing the portions of the n-type doped polysilicon layer and the second tunneling layer in the P region and the isolation region by using an alkali solution (such as a sodium hydroxide or potassium hydroxide solution), to only leave the second tunneling layer 22 and the n-type doped polysilicon layer 32 in the N region, and further texturing the light-receiving surface of the silicon substrate 10 and the isolation region to obtain a textured surface.

[0061] S300: forming a first conductive and heat-conductive layer 41 on the surface of the p-type doped polysilicon layer 31 or the side wall of the p-type doped polysilicon layer 31 near the isolation region, and / or forming a second conductive and heat-conductive layer 42 on the surface of the n-type doped polysilicon layer 32 or the side wall of the n-type doped polysilicon layer 32 near the isolation region.

[0062] According to some embodiments of the present application, the method of forming the first conductive and heat-conductive layer and / or the second conductive and heat-conductive layer comprises:

[0063] S310: forming a catalyst thin film (not shown in the figure) on the surface of the p-type doped polysilicon layer 31, the n-type doped polysilicon layer 32, and the silicon substrate in the isolation region.

[0064] In some embodiments of the present application, the material of the catalyst thin film comprises ferric nitrate. In the process of depositing the heat-conductive and conductive material layer, the iron ions are reduced to iron atoms by hydrogen in the deposition atmosphere, and the growth of the heat-conductive and conductive material, such as carbon nanotubes, is promoted under the catalysis of the iron atoms.

[0065] In some embodiments, the catalyst thin film is prepared by a sol-gel method, and the specific method can comprise: spin-coating a 0.1-0.2 mol / L ferric nitrate sol on the back surface of the substrate cell at a rotation speed of 2000-3000 rpm, and then performing drying and annealing treatment at 100-200 °C for 10-20 min to form a catalyst thin film with a thickness of 20-50 nm.

[0066] S320: depositing a heat-conductive and conductive material layer 04 on the surface of the catalyst thin film;

[0067] According to embodiments of the present application, the heat-conductive and conductive material layer is carbon nanotubes or carbon nanotubes and graphene. Taking carbon nanotubes as an example, the deposition conditions comprise: being performed in an atmosphere containing hydrogen and argon; the deposition temperature is 600-900 °C; the flow rate of H2 is 10-50 sccm, the flow rate of Ar is 30-120 sccm, and the flow rate of CH4 is 5-30 sccm; the deposition time is 10-30 min. Hydrogen can be pre-injected for a certain period of time (such as 5-10 min) before CH4 is injected, the iron ions on the surface of the catalyst thin film are pre-reduced by hydrogen, and then methane is injected, and carbon nanotubes are grown under the catalysis and promotion of iron to obtain a heat-conductive and conductive layer with a thickness of 5-10 nm.

[0068] S330: patterning the thermally and electrically conductive material layer 04 to obtain a first electrically and thermally conductive layer 41 and / or a second electrically and thermally conductive layer 42. The patterning of the thermally and electrically conductive material layer can refer to the design in Figures 1 to 8 , to obtain a first electrically and thermally conductive layer 41 and / or a second electrically and thermally conductive layer 42 as shown in Figures 1 to 8 . Figure 11

[0069] According to an embodiment of the present application, the thermally and electrically conductive material layer is patterned by laser method, and the power of the laser is 25-45 W, such as 25 W, 27 W, 30 W, 32 W, 35 W, 38 W, 40 W, 42 W, 45 W, etc. The laser under the above conditions can effectively pattern the thermally and electrically conductive material layer, and will not damage the p-type doped polysilicon layer and the n-type doped polysilicon layer

[0070] In some embodiments, the position irradiated by the laser in step S330 can be further cleaned by a hydrofluoric acid solution to repair the damage.

[0071] According to an embodiment of the present application, the thermally and electrically conductive layer has certain thermal conductivity and electrical conductivity, which will not affect the transport of carriers. The first thermally and electrically conductive layer forms a P+-P junction structure with the silicon material of the p-type doped polysilicon layer, has a certain "pumping" hole effect, can accelerate the separation and transport of carriers, and improves the performance of the solar cell. The second thermally and electrically conductive layer can form an effective built-in PN-like junction structure with the n-type doped polysilicon layer, suppresses the heat accumulation of the solar cell under shading, and at the same time, under the action of high thermal conductivity, can realize rapid and effective heat dissipation, reduce local thermal stress, relieve the hot spot effect, and protect the use of the solar cell.

[0072] According to some embodiments of the present application, the method for preparing a back contact solar cell further comprises: forming a first passivation layer 51 on the surface of the light-receiving side of the silicon substrate, and forming a second passivation layer 52 on the surface of the isolation region, the p-type doped polysilicon layer 31, the n-type doped polysilicon layer 32, and the thermally and electrically conductive layer 40 of the back side; forming a first anti-reflection layer 61 on the surface of the first passivation layer 51 away from the silicon substrate, and forming a second anti-reflection layer 62 on the surface of the second passivation layer 52 away from the silicon substrate; forming a first electrode 71 and a second electrode 72 on the back side, the first electrode 71 being in contact with the p-type doped polysilicon layer 31, and the second electrode 72 being in contact with the n-type doped polysilicon layer 32.

[0073] The first passivation layer and the second passivation layer can be deposited by atomic deposition method, and the first anti-reflection layer and the second anti-reflection layer can be prepared by plasma chemical vapor deposition (PECVD).

[0074] ​Further, the first electrode and the second electrode can be prepared by a screen printing method.

[0075] In yet another aspect of the present application, the present application provides a photovoltaic module. According to an embodiment of the present application, the photovoltaic module comprises the back contact solar cell as described above, or comprises the back contact solar cell prepared by the method as described above. Thus, the photovoltaic module has good heat dissipation efficiency and better cell performance. It is understood by those skilled in the art that the photovoltaic module has all the features and advantages of the back contact solar cell as described above, which will not be described in more detail herein.

[0076] Embodiment

[0077] Embodiment 1

[0078] The N-type silicon substrate is subjected to double-side polishing treatment in an alkaline etching tank of a wet process to remove surface dirt, damage, etc.

[0079] The first tunneling layer is deposited on the back surface of the silicon substrate by using the LPCVD method, and the deposition temperature can be 620°C, and the thickness of the first tunneling layer is 2 nm.

[0080] The first polysilicon layer is deposited on the surface of the first tunneling layer by using the LPCVD method, and the thickness of the first polysilicon layer is 290 nm, and the deposition temperature is 600°C.

[0081] The boron diffusion is performed on the first polysilicon layer, BCl3 is used as the boron source, boron deposition and diffusion are performed at 1000°C to form the p-type doped polysilicon layer, and then the boron-silicon glass (BSG) is formed, and the thickness of the BSG is 55 nm.

[0082] The BSG corresponding to the N region and the isolation region on the back surface is subjected to patterning treatment by using a 40W green picosecond laser, and then the laser-irradiated BSG is removed by using a hydrofluoric acid solution.

[0083] The p-type doped polysilicon layer part and the first tunneling layer part of the N region and the isolation region are removed by using a sodium hydroxide solution, and the etching is performed downward by 2.5 microns to remove the laser damage, and only the first tunneling layer 21 and the p-type doped polysilicon layer 31 of the P region are reserved.

[0084] The second tunneling layer is deposited on the back surface of the silicon substrate by using the LPCVD method, and the deposition temperature can be 610°C, and the thickness of the second tunneling layer is 1.90 nm.

[0085] The second polysilicon layer is deposited on the surface of the second tunneling layer by using the LPCVD method, and the thickness of the second polysilicon layer is 250 nm, and the deposition temperature is 610°C.

[0086] The second polysilicon layer is subjected to phosphorus diffusion, PCl3 is used as a boron source to deposit and diffuse boron to form an n-type doped polysilicon layer, and then a phosphor-silicon glass (PSG) is formed, and the thickness of the PSG is 50 nm;

[0087] A green picosecond laser is used to perform patterning on the PSG corresponding to the P region and the isolation region of the back surface, and the power of the laser can be 25-45 W, and then a hydrofluoric acid solution is used to remove the PSG irradiated by the laser;

[0088] The n-type doped polysilicon layer and the second tunneling layer of the P region and the isolation region are removed by using a sodium hydroxide solution, and only the second tunneling layer 22 and the n-type doped polysilicon layer 32 of the N region are reserved, and further, the light-receiving surface and the isolation region of the silicon substrate 10 are textured to obtain a textured surface;

[0089] An iron nitrate sol of 0.15 mol / L is spin-coated on the back surface of the base cell at a speed of 2500 rpm, and then baked and annealed at 150°C for 15 min to form a catalyst film with a thickness of 35 nm;

[0090] A carbon nanotube material layer with a thickness of nm is deposited on the surface of the catalyst film, and the deposition conditions include: being performed in an atmosphere containing hydrogen and argon; the deposition temperature is 750°C; the flow rate of H2 is 35 sccm, the flow rate of Ar is 80 sccm, and the flow rate of CH4 is 20 sccm; the deposition time is 15 minutes. Before CH4 is introduced, 8 min of hydrogen and argon can be introduced in advance;

[0091] A green picosecond laser is used to irradiate the carbon nanotube material layer to achieve patterning of the carbon nanotube material layer, and the power is 30 W to obtain a first conductive and heat-conductive layer 41 covering the p-type doped polysilicon layer, as shown in Figure 1 ;

[0092] HF solution is used to clean and repair the damage in the laser irradiation area of the previous step;

[0093] Aluminum oxide material first and second passivation layers with a thickness of 4 nm are respectively formed on the light-receiving surface and the back surface of the cell substrate by atomic deposition;

[0094] A first anti-reflective layer is deposited on the surface of the first passivation layer by PECVD, and a second anti-reflective layer is deposited on the surface of the second passivation layer, the first anti-reflective layer includes a silicon nitride layer, a silicon oxynitride layer and a silicon nitride layer stacked, and the thickness is 70 nm, the second anti-reflective layer includes a silicon nitride layer, a silicon oxynitride layer and a silicon nitride layer stacked, and the thickness is 82 nm;

[0095] The first electrode is formed by printing silver paste on the P region of the back surface by screen printing, and the second electrode is formed by printing silver paste on the N region, thereby obtaining a back contact solar cell.

[0096] Example 2

[0097] The method and structure for preparing the back contact solar cell are basically the same as those in Example 1, except that the second conductive and heat-conductive layer 41 covering part of the surface of the n-type doped polysilicon layer is prepared, as shown in Figure 3 .

[0098] Example 3

[0099] The method and structure for preparing the back contact solar cell are basically the same as those in Example 1, except that the first conductive and heat-conductive layer 41 covering the surface of the p-type doped polysilicon layer is prepared, and the second conductive and heat-conductive layer 41 covering part of the surface of the n-type doped polysilicon layer is prepared, as shown in Figure 5 .

[0100] Comparative Example 1

[0101] The method and structure for preparing the back contact solar cell are basically the same as those in Example 1, except that the structure of the heat-conductive and conductive layer is not prepared, i.e., after forming the texture, the preparation of the passivation layer is directly performed.

[0102] The back contact solar cells prepared in Examples 1-3 and Comparative Example 1 are subjected to cell efficiency and conventional hot spot temperature detection, and the test results are shown in Table 1.

[0103] Table 1

[0104]

[0105] As can be seen from the data in Table 1, the reverse bias voltage in Examples 1, 2 and 3, where the conductive and heat-conductive layer exists, is less than that in Comparative Example 1, where the conductive and heat-conductive layer does not exist. At the same time, due to the effect of the structure, it helps to separate the carriers of the P region material, reducing the electrical loss caused by the hot spot effect. At the same time, although the hot spot effect still exists in Examples 1-3, the overall module temperature is reduced due to the arrangement of the heat-conductive and conductive layer.

[0106] In addition, the cell efficiency gain data in Examples 1-3 in Table 1 is compared with the cell efficiency of Comparative Example 1. Although the cell efficiency of Examples 1-3 is slightly lower than that of Comparative Example 1, the efficiency loss is very small, and it basically does not cause great loss to the overall cell efficiency of the battery module. Therefore, the negative effect of the heat-conductive and conductive layer on the cell efficiency can be ignored.

[0107] The terms "first", "second", etc. are used only for the purpose of description and are not to be interpreted in a relative manner or to imply relative importance or to imply a number of the technical features indicated. Thus, the features defined with "first", "second" can include one or more of the features explicitly or implicitly. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0108] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present application and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0109] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A back-contact solar cell, comprising: A silicon substrate, comprising an N-region, a P-region, and an isolation region between the N-region and the P-region on the backlight surface of the silicon substrate, wherein the P-region includes a first tunneling layer and a p-type doped polysilicon layer, and the N-region includes a second tunneling layer and an n-type doped polysilicon layer, wherein the first tunneling layer is disposed on the surface of the silicon substrate corresponding to the P-region, and the second tunneling layer is disposed on the surface of the silicon substrate corresponding to the N-region. The p-type doped polysilicon layer is disposed on the side of the first tunneling layer away from the silicon substrate, and the n-type doped polysilicon layer is disposed on the side of the second tunneling layer away from the silicon substrate. The feature is that it further includes: a p-type material thermally conductive layer, the thermally conductive layer including a first thermally conductive layer and / or a second thermally conductive layer, the first thermally conductive layer being disposed on at least a portion of the surface of the p-type doped polysilicon layer away from the silicon substrate or located on the sidewall of the p-type doped polysilicon layer near the isolation region, and the second thermally conductive layer being disposed on at least a portion of the surface of the n-type doped polysilicon layer away from the silicon substrate or located on the sidewall of the n-type doped polysilicon layer near the isolation region.

2. The back-contact solar cell according to claim 1, characterized in that, The first thermally and electrically conductive layer extends from the P region to the isolation region.

3. The back-contact solar cell according to claim 1 or 2, characterized in that, The second thermally and electrically conductive layer extends from the N region to the isolation region.

4. The back-contact solar cell according to claim 1, characterized in that, The thickness of the thermally and electrically conductive layer is 5–10 nm.

5. The back-contact solar cell according to claim 1, characterized in that, The material of the thermally and electrically conductive layer includes at least one of graphene and carbon nanotubes.

6. A method for preparing a back-contact solar cell according to any one of claims 1 to 5, characterized in that, include: A first tunneling layer and a p-type doped polycrystalline silicon layer are sequentially formed in the P region of the silicon substrate; A second tunneling layer and an n-type doped polycrystalline silicon layer are sequentially formed in the N region of the silicon substrate; A first conductive and thermally conductive layer is formed on the surface of the p-type doped polysilicon layer or on the sidewall of the p-type doped polysilicon layer near the isolation region, and / or a second conductive and thermally conductive layer is formed on the surface of the n-type doped polysilicon layer or on the sidewall of the n-type doped polysilicon layer near the isolation region.

7. The method according to claim 6, characterized in that, The method of forming the first conductive and thermally conductive layer and / or the second thermally conductive and conductive layer includes: A catalyst film is formed on the silicon substrate surface of the p-type doped polysilicon layer, the n-type doped polysilicon layer, and the isolation region. A thermally and electrically conductive material layer is deposited on the surface of the catalyst film; The thermally and electrically conductive material layer is patterned to obtain the first thermally and electrically conductive layer and / or the second thermally and electrically conductive layer.

8. The method according to claim 7, characterized in that, The catalyst film is made of ferric nitrate.

9. The method according to claim 7, characterized in that, The thermally and electrically conductive material layer is carbon nanotubes, and the deposition conditions include: It is carried out in an atmosphere containing hydrogen and argon; The deposition temperature is 600-900℃; The flow rate of H2 is 10-50 sccm, the flow rate of Ar is 30-120 sccm, and the flow rate of CH4 is 5-30 sccm. The deposition time is 10 to 30 minutes.

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

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