Preparation method for TBC solar cell

Abstract

The present invention relates to the field of solar cells. Disclosed is a preparation method for a TBC solar cell. In the present invention, a mask is formed on a single i-poly-Si layer by means of ultraviolet laser-induced oxidation, and doping diffusion is performed, so as to obtain a TBC solar cell. The whole preparation process requires only one i-poly-Si deposition and one laser grooving operation, thereby avoiding problems such as reduced product performance and yield due to uneven thermal stress distribution caused by multiple i-poly-Si depositions; meanwhile, one laser grooving operation can reduce damage to a silicon wafer, and increase Voc; in addition, the use of one i-poly-Si deposition can also greatly reduce the amount of a specialty gas and reduce the production cost. In addition, in the TBC solar cell prepared by the method of the present invention, the i-poly-Si layer and an n+-poly-Si layer formed on the back surface of the silicon wafer have substantially the same height, facilitating subsequent preparation of electrode layers and further improving product performance and yield.

Description

A preparation method of a TBC solar cell TECHNICAL FIELD

[0001] The present application relates to the field of solar cells, in particular to a preparation method of a TBC solar cell. BACKGROUND

[0002] The Chinese name of IBC cell is cross finger back contact cell. The positive surface of the cell has no metal grid line, and the positive surface / back surface and the corresponding positive / negative metal electrodes are integrated in a cross finger shape on the back surface of the cell. This unique structure avoids the shading of the metal grid electrode to the light (~3%), and combines the pyramid structure and the anti-reflection layer on the front and back surfaces to maximize the use of incident light. Compared with other technical routes of solar cells such as PERC and TOPCon, the optical loss can be reduced more, the short-circuit current is higher, and the photoelectric conversion efficiency can be effectively improved. IBC cell mainly improves the conversion efficiency through structural changes, and is a relatively pure single-sided cell. As a post-TOPCon+ technology, TBC solar cell combines the excellent tunneling oxide / doped polysilicon passivation contact structure technology of TOPCon, and is expected to become a new generation of mass-produced cells.

[0003] The current preparation of TBC solar cell usually needs to sequentially deposit p + -poly-Si(≥200nm), n + -poly-Si(≥200nm) on the back surface of the cell, and then form corresponding laser grooving process. For example, a Chinese patent with publication number CN116845140A discloses a preparation method of a TBC solar cell, which comprises: performing structural treatment and alkali polishing on a silicon wafer, depositing a first tunneling SiO x layer and a first polysilicon layer on the back surface, forming a mask BSG layer by boron doping, first grooving and cleaning, depositing a second tunneling SiO x layer and a second polysilicon layer on the back surface, forming a mask PSG layer by phosphorus doping, second grooving, cleaning and simultaneously double-side texturing, depositing an AlO x layer on the back surface, depositing SiN x anti-reflection film on the back surface and the front surface respectively, performing screen printing, sintering and testing and sorting. The TBC solar cell formed by the above scheme uses the characteristics that the mask does not react with alkali, and then laser local ablation and wet chemical cleaning are performed to repair laser damage, and the doping atoms remaining on the surface during laser ablation are also washed away. At the same time, the front surface and the grooved area on the back surface are textured to improve the passivation performance of the front surface, enhance the long-wave band light response, and improve the open-circuit voltage of the cell, thereby further improving the conversion efficiency of the cell.

[0004] However, in the process, since the back surface of the silicon wafer needs to be deposited with poly-Si twice, uneven distribution of thermal stress is prone to occur, thereby causing abnormal problems such as silicon wafer warping and fragmentation, affecting product performance, and the yield is low; meanwhile, the amount of special gas required for depositing double-layer poly-Si is greatly increased, increasing the preparation cost. SUMMARY

[0005] To solve the above technical problems, the present application provides a preparation method of a TBC solar cell, which obtains the TBC solar cell by doping diffusion through a single-layer i-poly-Si layer combined with ultraviolet laser oxidation to form an oxidation barrier layer. The method only needs one i-poly-Si deposition and one laser slotting process in the whole process, which can effectively improve the performance and yield of the product, and at the same time significantly reduce the production cost. In addition, the formation of the oxidation barrier layer by ultraviolet laser oxidation is a simple, efficient and low-cost method, which is expected to be widely used in production lines.

[0006] The specific technical scheme of the present application is as follows: a preparation method of a TBC solar cell, specifically comprising the following steps: S1, polishing both sides of the silicon wafer.

[0007] S2, sequentially depositing a tunneling SiO x layer, an i-poly-Si layer on the back surface of the silicon wafer.

[0008] S3, using ultraviolet laser to pattern and oxidize the surface of the i-poly-Si layer once to form a first oxidation barrier layer. The imaged first oxidation barrier layer and the subsequent second oxidation barrier layer are interdigitated and complementary, and their sum just covers the entire i-poly-Si layer. The first oxidation barrier layer corresponds to the range of the subsequent n + -ploy-Si (phosphorus-doped polycrystalline silicon) layer, and the unblocked area thereof is diffused by boron atoms to form a p + -ploy-Si (boron-doped polycrystalline silicon) layer during the boron diffusion process; the second oxidation barrier layer corresponds to the range of the subsequent p + -ploy-Si layer, and the unblocked area thereof is diffused by phosphorus atoms to form an n + -ploy-Si layer during the phosphorus diffusion process.

[0009] In the ultraviolet laser oxidation process, oxygen or ozone is dissociated into oxygen ions under the action of the laser emitted by the ultraviolet laser, and the oxygen ions and the surface of the silicon wafer are oxidized to form a silicon oxide layer (oxidation barrier layer) as a mask. In this process, the laser emitted by the laser simultaneously heats the silicon wafer, which is conducive to promoting the rapid oxidation reaction of the oxygen ions and the silicon wafer to generate the silicon oxide layer as a mask, so that the preparation of the mask can be quickly completed. Compared with the deposition process for preparing the mask, the mask preparation time can be greatly shortened, and the mask preparation efficiency and accuracy can be improved.

[0010] S4, boron diffusion is performed on the i-poly-Si layer with the first oxidation barrier layer, boron atoms are more difficult to enter the bottom i-poly-Si layer in the region with the first oxidation barrier layer, so that the intrinsic poly-Si characteristics can still be maintained; for the i-poly-Si layer without the oxidation barrier layer, the i-poly-Si layer can be converted into p + -poly-Si layer, and a BSG layer (boron-silicon glass layer) is generated on the surface.

[0011] S5, the first oxidation barrier layer and the BSG layer are removed. The first oxidation barrier layer covering the surface of the i-poly-Si layer and the BSG layer covering the surface of the p + -poly-Si layer are removed, so that the second oxidation barrier layer can be formed on the surface of the p + -poly-Si layer by ultraviolet laser oxidation in the subsequent process, and the remaining i-poly-Si layer is exposed to phosphorus diffusion, so that the phosphorus atoms can enter. After the first oxidation barrier layer and the BSG layer are removed, the back surface of the silicon wafer is the i-poly-Si layer and the p + -poly-Si layer which are spaced and intersected with each other.

[0012] S6, the p + -poly-Si layer is secondly patterned by ultraviolet laser to form the second oxidation barrier layer.

[0013] S7, phosphorus diffusion is performed on the region without the second oxidation barrier layer to generate n + -poly-Si layer and a PSG layer (phosphorus-silicon glass layer).

[0014] S8, the scribe layer on the front surface and the side surface of the silicon wafer is removed. The scribe layer is removed before laser scribing in the present application, because the scribe layer is generally removed by etching with a mixture of acids, and the i-poly-Si layer and the n + -poly-Si layer are exposed after scribing, and if the scribe layer is removed after scribing, the i-poly-Si layer or the tunneling SiO + layer or the silicon wafer itself exposed after scribing will be corroded by the acid solution, thereby affecting the performance of the prepared battery. x

[0015] S9, laser scribing is performed at the junction of the p + -poly-Si layer and the n + -poly-Si layer.

[0016] S10, both surfaces are textured and cleaned to remove the second oxidation barrier layer and the PSG layer.

[0017] ​S11, double-sided coating, generating passivation anti-reflective layer on the front / back side. Coating passivation anti-reflective layer on the surface of the silicon wafer prepared initially, the purpose is: (1) reducing surface carrier recombination, improving V oc ; (2) reducing light reflection and increasing more light absorption, increasing photocurrent.

[0018] S12, screen printing, sintering, light injection, obtaining TBC solar cell.

[0019] In the above preparation method, the present application first carries out double-sided polishing treatment on the silicon wafer, then deposits tunneling SiO x layer and i-poly-Si layer on the back side of the silicon wafer successively; then, based on the single-layer i-poly-Si layer, pre-determines the surface as the pattern range of n + -ploy-Si layer region and p + -ploy-Si layer region, forms first oxidation barrier layer on the surface of the i-poly-Si layer corresponding to the n + -ploy-Si layer region by UV laser oxidation treatment to protect, generates p + -ploy-Si layer by boron diffusion on the unprotected region; after removing the first oxidation barrier layer and BSG layer, forms second oxidation protection layer on the surface of the generated p + -ploy-Si layer to protect, generates n + -ploy-Si layer by phosphorus diffusion on the unprotected i-poly-Si layer; thus, the generation of P + region (p + -ploy-Si) and N + region (n + -ploy-Si) on the single-layer i-poly-Si layer is completed, then laser grooving is carried out on the junction of the two regions to realize insulation isolation, then texturing, double-sided coating and electrode layer setting are carried out, finally TBC solar cell is prepared.

[0020] As described in the background section of the present application, in the prior art, multiple polycrystalline silicon layers (i-poly-Si layers) need to be deposited and laser grooving needs to be carried out multiple times in the whole preparation process. Among them, multiple deposition is prone to uneven thermal stress distribution, resulting in problems such as wafer warping, fragmentation and low yield; at the same time, multiple laser grooving increases the damage to the silicon wafer; in addition, multiple deposition also greatly increases the amount of special gas, increasing the production cost. In the whole preparation process of the present application, only one i-poly-Si deposition is needed, which can avoid the problems of uneven thermal stress distribution caused by multiple i-poly-Si deposition, resulting in low yield; at the same time, one laser grooving can reduce the damage to the silicon wafer, improving V oc; In addition, the one-time i-poly-Si deposition can greatly reduce the consumption of special gas and reduce the production cost. In addition, the present application forms a mask (oxidation barrier layer) on the surface of the silicon wafer by laser oxidation, which is a simple, efficient and low-cost method, and is expected to be widely used in production lines.

[0021] As preferred, in S3, the forming process of the first oxidation barrier layer includes: once patterning oxidation of the i-poly-Si layer by ultraviolet laser, under the conditions of pre-set n + The i-poly-Si region forms the first oxidation barrier layer; the wavelength of the ultraviolet laser is 300-400 nm, the power is 10-500 W, and the processing time is 1-20 s; and a first oxidation barrier layer with a thickness of 20-300 nm is formed.

[0022] As another preferred, in S3, the forming process of the first oxidation barrier layer is first ultraviolet laser oxidation treatment in a low-concentration oxygen environment, and then ultraviolet laser oxidation treatment in a high-concentration oxygen environment, to finally form a dense first oxidation barrier layer. Specifically, it includes: first, under the conditions of a tube-passing O2 flow rate of 10-100 sccm, an oxygen concentration of 20-30% in the environment, an ultraviolet laser wavelength of 300-400 nm, a power of 10-500 W, and a processing time of 1-20 s, the i-poly-Si layer region surface is formed with a first oxidation barrier layer with a thickness of 20-300 nm. + The i-poly-Si layer region surface is formed with a first oxidation barrier layer with a thickness of 20-300 nm.

[0023] Then, under the conditions of a tube-passing O2 flow rate of 100-500 sccm, an oxygen concentration of 30-80% in the environment, an ultraviolet laser wavelength of 200-300 nm, a power of 2-50 W, and a processing time of 1-20 s, a more dense first oxidation barrier layer is formed.

[0024] The reason for adopting the above-mentioned distributed differential ultraviolet laser oxidation process is that the present application finds that the oxidation barrier layer formed by the conventional one-step ultraviolet laser oxidation process is often not dense enough, which easily increases the risk of boron atoms and phosphorus atoms in the subsequent boron diffusion and phosphorus diffusion process to diffuse into the bottom i-poly-Si layer, thereby causing battery leakage or performance degradation. The above-mentioned distributed differential ultraviolet laser oxidation process of the present application can make the oxygenated barrier layer more dense, and the principle is that different laser wavelengths penetrate to different depths in the silicon. In the first step, the wavelength is larger and the penetration depth is deeper, which can make the i-poly-Si layer surface oxidation barrier layer thicker; in the second step, the wavelength is shorter and the penetration depth is shallower, which can make the oxidation barrier layer become more dense without changing the thickness; at the same time, under different oxygen concentration processing environments, the formed oxidation barrier layer can more effectively block the subsequent boron and phosphorus atom diffusion, thereby improving the battery performance.

[0025] As preferred, in S6, the forming process of the second oxidation barrier layer comprises: UV laser secondary patterning and oxidizing p + poly-Si layer to form the second oxidation barrier layer; the wavelength of the UV laser is 300-400 nm, the power is 10-500 W, and the processing time is 1-20 s; and a first oxidation barrier layer with a thickness of 20-300 nm is formed.

[0026] As another preferred, in S6, the forming process of the second oxidation barrier layer comprises: first UV laser oxidation treatment in a low-concentration oxygen environment, and then UV laser oxidation treatment in a high-concentration oxygen environment, to finally form a dense second oxidation barrier layer, which specifically comprises: first, under the conditions of a tube-passing O2 flow of 10-100 sccm, an oxygen concentration of 20-30% in the environment, a UV laser wavelength of 300-400 nm, a power of 10-500 W, and a processing time of 1-20 s, UV laser oxidation treatment is performed on the p + poly-Si layer to form a second oxidation barrier layer with a thickness of 20-300 nm; and then, under the conditions of a tube-passing O2 flow of 100-500 sccm, an oxygen concentration of 30-80% in the environment, a UV laser wavelength of 200-300 nm, a power of 2-50 W, and a processing time of 1-20 s, a more dense second oxidation barrier layer is formed.

[0027] As preferred, in S1, the double-side polishing process comprises: putting a single crystal silicon wafer with a resistivity of 1-12 Ω·cm, a minority carrier lifetime of >2.5 ms, and a thickness of 100-200 μm into an alkali polishing tank containing alkali solution, and double-side polishing at 75-85 ℃ for 6-8 min, so that the polishing thickness is 3-7 μm, and the thinning amount is 0.35-0.45 g.

[0028] As preferred, in S2, when the tunneling SiO x layer is deposited, the gas flow of O2 is 10000-80000 sccm, the reaction temperature is 400-800 ℃, the time is 200-1000 s, and the thickness of the tunneling SiO x layer is 2-10 nm.

[0029] As preferred, in S2, when the i-poly-Si layer is deposited on the tunneling SiO x layer, the gas flow of SiH4 is 300-2000 sccm, the reaction temperature is 500-700 ℃, the time is 2-4 h, the working gas pressure is 100-500 mTorr, and the thickness of the i-poly-Si layer is 100-300 nm.

[0030] As preferred, in S4, the process of boron diffusion comprises: firstly, passing mixed gas of BCl3 and O2, temperature is 800-950℃, diffusion time is 5-50min, BCl3 gas flow is 50-500sccm, O2 flow is 500-2000sccm; secondly, passing O2 to perform oxidation promotion, temperature is 900-1050℃, promotion time is 30-80min, O2 flow is 5000-30000sccm, to generate BSG layer with thickness of 30-70nm.

[0031] As preferred, in S7, the process of phosphorus diffusion comprises: firstly, passing mixed gas of POCl3 and O2, temperature is 750-850℃, diffusion time is 5-30min, POCl3 flow carried by nitrogen is 500-1200sccm, oxygen flow is 500-1000sccm; secondly, passing O2 to perform oxidation promotion, temperature is 850-950℃, promotion time is 20-60min, O2 flow is 1000-10000sccm, to generate PSG layer with thickness of 30-70nm.

[0032] As preferred, in S8, the step of removing the wrap-plating layer on the front side and side of the silicon wafer comprises: removing the wrap-plating layer on the front side and side of the silicon wafer by adopting chain etching machine, volume ratio of hydrofluoric acid solution and nitric acid solution in acid tank is 1:2-1:8, concentration of the hydrofluoric acid solution is 45-55wt%, concentration of the nitric acid solution is 65-75wt%, and belt speed is 1-10m / min.

[0033] As preferred, in S9, the condition of laser slotting is: laser wavelength is 400-600nm, frequency is 500-700KHz, marking speed is 40000-50000mm / s, power is 10-50W, and processing time is 1-5s.

[0034] As preferred, in S11, after the double-side film plating, passivation anti-reflection layer is generated on the front side and back side, which comprises AlO x thin film with thickness of 8-10nm, SiN x thin film with thickness of 80-120nm deposited on the AlO x thin film.

[0035] Compared with prior art, the present application has the following advantages: (1) the present application adopts single-layer i-poly-Si layer combined with ultraviolet laser patterning oxidation to form oxidation barrier layer for doping diffusion to obtain TBC solar cell, the whole preparation process only needs once i-poly-Si deposition and once laser slotting process, which can avoid problems such as uneven distribution of thermal stress caused by multiple i-poly-Si deposition, product performance and yield reduction, etc.; meanwhile, once laser slotting can reduce damage to the silicon wafer, and improve Voc ; in addition, the adoption of the once polysilicon layer deposition can greatly reduce the consumption of special gas and reduce the production cost.

[0036] (2) Compared with the conventional process such as deposition process for preparing a mask, the ultraviolet laser oxidation form of the present application can greatly shorten the preparation time of the mask (oxidation barrier layer), improve the preparation efficiency and preparation precision of the mask, and is a simple, efficient and low-cost method, which is expected to be widely used in production lines.

[0037] (3) In the TBC solar cell prepared by the method of the present application, the height of the n + -ploy-Si layer on the back of the silicon wafer and the height of the p + -ploy-Si layer are basically the same, which is helpful for the preparation of the subsequent electrode layer and can further improve the product yield. BRIEF DESCRIPTION OF DRAWINGS

[0038] Fig. 1 is a schematic structural diagram of a TBC solar cell of the present application.

[0039] Fig. 2 is a schematic structural diagram of a silicon wafer after cutting in Example 1 of the present application.

[0040] Fig. 3 is a schematic structural diagram of a silicon wafer after double polishing in Example 1 of the present application.

[0041] Fig. 4 is a schematic structural diagram of a silicon wafer after deposition of a tunneling SiO x layer and an i-poly-Si layer in Example 1 of the present application.

[0042] Fig. 5 is a schematic structural diagram of a silicon wafer after generating a first oxidation barrier layer in Example 1 of the present application.

[0043] Fig. 6 is a schematic structural diagram of a silicon wafer after boron diffusion in Example 1 of the present application.

[0044] Fig. 7 is a schematic structural diagram of a silicon wafer after generating a second oxidation barrier layer in Example 1 of the present application.

[0045] Fig. 8 is a schematic structural diagram of a silicon wafer after phosphorus diffusion in Example 1 of the present application.

[0046] Fig. 9 is a schematic structural diagram of a silicon wafer after laser grooving in Example 1 of the present application.

[0047] Fig. 10 is a schematic structural diagram of a silicon wafer after texturing in Example 1 of the present application.

[0048] The reference signs are: cutting line mark 1; N-type monocrystalline silicon wafer 2; tunneling SiO x layer 3; i-poly-Si layer 4; first oxidation barrier layer 5; p + -ploy-Si layer 6; second oxidation barrier layer 7; n +- ploy-Si layer 8; pyramid suede 9; front passivation anti-reflection layer 10; back passivation anti-reflection layer 11; electrode layer 12. DETAILED DESCRIPTION

[0049] The application will be further described in connection with the following examples.

[0050] A preparation method of a TBC solar cell, specifically comprising the following steps: S1, polishing both sides of a silicon wafer.

[0051] In some specific embodiments, the process of double-side polishing comprises: putting a single crystal silicon wafer with a thickness of 100-200 μm into an alkali polishing tank containing alkali liquor, and polishing both sides at 75-85 ℃ for 6-8 min, with a polishing thickness of 3-7 μm and a thinning amount of 0.35-0.45 g.

[0052] S2, sequentially depositing a tunneling SiO x layer, an i-poly-Si layer on the back side of the silicon wafer.

[0053] LPCVD has better step coverage, good composition and structure control, high deposition rate and output, and can greatly reduce the particle pollution source.

[0054] In some specific embodiments, when depositing the tunneling SiO x layer, the gas flow of O2 is 10000-80000 sccm, the reaction temperature is 400-800 ℃, the time is 200-1000 s, and the thickness of the tunneling SiO x layer is 2-10 nm.

[0055] In some specific embodiments, when depositing the i-poly-Si layer on the tunneling SiO x layer, the gas flow of SiH4 is 300-2000 sccm, the reaction temperature is 500-700 ℃, the time is 2-4 h, the working gas pressure is 100-500 mTorr, and the thickness of the i-poly-Si layer is 100-300 nm.

[0056] S3, using ultraviolet laser to pattern the surface of the i-poly-Si layer once to form a first oxidation barrier layer. The imaged first oxidation barrier layer and the subsequent second oxidation barrier layer are interdigitated and complementary, and the sum of the two just covers the entire i-poly-Si layer. The first oxidation barrier layer corresponds to the range of the subsequent n + -ploy-Si (phosphorus-doped polycrystalline silicon) layer, and the unblocked area thereof is diffused by boron atoms to form a p +-ploy-Si (boron-doped polysilicon) layer; the second oxidation barrier layer corresponds to the p + -ploy-Si layer, whose unblocked region is diffused by phosphorus atoms during the phosphorus diffusion process to form an n + -ploy-Si layer.

[0057] In some specific embodiments, the generation process of the first oxidation barrier layer includes: ultraviolet laser one-time patterning of the i-poly-Si layer, and ultraviolet laser oxidation of the n + -poly-Si region to form the first oxidation barrier layer; the wavelength of the ultraviolet laser is 300-400 nm, the power is 10-500 W, and the processing time is 1-20 s; and a 20-300 nm thick first oxidation barrier layer is generated.

[0058] In the above process, oxygen or ozone is dissociated into oxygen ions under the action of laser emitted by the ultraviolet laser, and the oxygen ions and the silicon wafer surface undergo an oxidation reaction to generate a silicon oxide layer (oxidation barrier layer) as a mask. In this process, the laser emitted by the laser simultaneously heats the silicon wafer, which is beneficial to promote the rapid oxidation reaction of the oxygen ions and the silicon wafer to generate the silicon oxide layer as a mask, and the preparation of the mask can be quickly completed. Compared with the deposition process for preparing the mask, the mask preparation time can be greatly shortened, and the mask preparation efficiency and preparation precision can be improved.

[0059] In some more preferred embodiments, the generation process of the first oxidation barrier layer is first ultraviolet laser oxidation treatment in a low-concentration oxygen environment, and then ultraviolet laser oxidation treatment in a high-concentration oxygen environment, to finally form a dense first oxidation barrier layer. Specifically, first, under the conditions of a tube-passing O2 flow rate of 10-100 sccm, an oxygen concentration in the environment of 20-30%, an ultraviolet laser wavelength of 300-400 nm, a power of 10-500 W, and a processing time of 1-20 s, the n + -poly-Si layer region surface generates a 20-300 nm thick first oxidation barrier layer.

[0060] Then, under the conditions of a tube-passing O2 flow rate of 100-500 sccm, an oxygen concentration in the environment of 30-80%, an ultraviolet laser wavelength of 200-300 nm, a power of 2-50 W, and a processing time of 1-20 s, a more dense first oxidation barrier layer is formed.

[0061] The reason for using the above-mentioned distributed differential ultraviolet laser oxidation process is that the inventor finds that the oxidation barrier layer formed by using a conventional one-step ultraviolet laser oxidation process is often not dense enough, which easily increases the risk of boron atoms and phosphorus atoms diffusing into the bottom i-poly-Si layer during subsequent boron diffusion and phosphorus diffusion processes, thereby causing the battery performance to decrease or to leak. The above-mentioned distributed differential ultraviolet laser oxidation process of the present application can make the oxygenated barrier layer denser, and the principle is that different laser wavelengths penetrate to different depths in the silicon, the wavelength is larger in the first step, the penetration depth is deeper, which can make the surface oxidation barrier layer of the i-poly-Si layer thicker; the wavelength is shorter in the second step, the penetration depth is shallower, which can make the oxidation barrier layer more dense without changing the thickness; and the oxygen concentration in the processing environment is different, which makes the oxidation barrier layer more effective in blocking the subsequent boron and phosphorus atoms from diffusing inward.

[0062] S4, boron diffusion is performed on the i-poly-Si layer containing the first oxidation barrier layer, and it is more difficult for boron atoms in the region with the first oxidation barrier layer to diffuse into the bottom i-poly-Si layer, so that the intrinsic poly-Si characteristics can still be maintained; for the i-poly-Si layer without the oxidation barrier layer, it can be converted into a p + -poly-Si layer during the boron diffusion process, and a BSG layer (boron-silicon glass layer) is generated on the surface.

[0063] In some specific embodiments, the boron diffusion process includes: first, passing a mixed gas of BCl3 and O2, the temperature is 800-950℃, the diffusion time is 5-50min, the BCl3 gas flow rate is 50-500sccm, and the O2 flow rate is 500-2000sccm; and then, passing O2 for oxidation promotion, the temperature is 900-1050℃, the promotion time is 30-80min, the O2 flow rate is 5000-30000sccm, and a 30-70nm-thick BSG layer is generated.

[0064] S5, removing the first oxidation barrier layer and the BSG layer. The first oxidation barrier layer covering the surface of the i-poly-Si layer and the BSG layer covering the surface of the p + -poly-Si layer are removed, so that the second oxidation barrier layer can be formed on the surface of the p + -poly-Si layer by ultraviolet laser oxidation in the subsequent process, and the remaining i-poly-Si layer is exposed to facilitate the entry of phosphorus atoms. After the first oxidation barrier layer and the BSG layer are removed, the back surface of the silicon wafer is the i-poly-Si layer and the p + -poly-Si layer which are spaced apart and intersected with each other.

[0065] S6, performing secondary patterning on the p +- poly-Si layer surface, forming a second oxidation barrier layer.

[0066] In some specific embodiments, the process of forming the second oxidation barrier layer comprises: UV laser secondary patterning oxidation of p + - poly-Si layer, forming a second oxidation barrier layer; the wavelength of the UV laser is 300-400 nm, the power is 10-500 W, and the processing time is 1-20 s; a first oxidation barrier layer with a thickness of 20-300 nm is formed.

[0067] In some more preferred embodiments, the process of forming the second oxidation barrier layer is first UV laser oxidation treatment in a low-concentration oxygen environment, and then UV laser oxidation treatment in a high-concentration oxygen environment, finally forming a dense second oxidation barrier layer, which specifically comprises: first, under the conditions of a tube-passing O2 flow rate of 10-100 sccm, an oxygen concentration in the environment of 20-30%, a UV laser wavelength of 300-400 nm, a power of 10-500 W, and a processing time of 1-20 s, UV laser oxidation treatment is performed on the p + - poly-Si layer surface to form a second oxidation barrier layer with a thickness of 20-300 nm; then, under the conditions of a tube-passing O2 flow rate of 100-500 sccm, an oxygen concentration in the environment of 30-80%, a UV laser wavelength of 200-300 nm, a power of 2-50 W, and a processing time of 1-20 s, a more dense second oxidation barrier layer is formed.

[0068] S7, phosphorus diffusion is performed on the area without the second oxidation barrier layer to form an n + - poly-Si layer and PSG layer (phosphosilicate glass layer).

[0069] In some specific embodiments, the process of phosphorus diffusion comprises: first, a mixed gas of POCl3 and O2 is passed in, the temperature is 750-850°C, the diffusion time is 5-30 min, the flow rate of POCl3 carried by nitrogen is 500-1200 sccm, and the flow rate of oxygen is 500-1000 sccm; then, O2 is passed in for oxidation promotion, the temperature is 850-950°C, the promotion time is 20-60 min, the flow rate of O2 is 1000-10000 sccm, and a PSG layer with a thickness of 30-70 nm is formed.

[0070] S8, the scribe layer on the front and side surfaces of the silicon wafer is removed. The present application specifically removes the scribe layer before laser scribing, because when the scribe layer is removed, the excess p + - poly-Si layer and n + - poly-Si layer, if scribing is performed first and then the scribe layer is removed, the i-poly-Si layer or tunneling SiOx The layer or the silicon wafer itself is eroded by the acid solution, thereby affecting the performance of the prepared battery.

[0071] In some specific embodiments, the step of removing the wrap plating layer on the front and side surfaces of the silicon wafer comprises: removing the wrap plating layer on the front and side surfaces of the silicon wafer by using a chain etching machine, and the volume ratio of the hydrofluoric acid solution to the nitric acid solution in the acid tank is 1:2-1:8, wherein the concentration of the hydrofluoric acid solution is 45-55 wt%, the concentration of the nitric acid solution is 65-75 wt%, and the tape speed is 1-10 m / min.

[0072] S9, etching the back surface of the silicon wafer to form a p + -poly-Si layer and n + laser grooving at the junction of the -poly-Si layer.

[0073] In some specific embodiments, the laser grooving conditions are as follows: the laser wavelength is 400-600 nm, the frequency is 500-700 KHz, the marking speed is 40,000-50,000 mm / s, the power is 10-50 W, and the processing time is 1-5 s.

[0074] S10, double-side texturing and cleaning to remove the second oxidation barrier layer and the PSG layer.

[0075] After the texturing is completed, the residual PSG layer and the second oxidation barrier layer on the back surface of the silicon wafer are further removed. Finally, the p + -ploy-Si layer and n + -ploy-Si layer.

[0076] S11, double-side film plating to form a passivation anti-reflection layer on the front / back surfaces. A passivation anti-reflection layer is plated on the surface of the silicon wafer prepared initially, and the purpose is to: (1) reduce the surface carrier recombination and improve the V oc ; (2) reduce the light reflection and increase more light absorption, thereby increasing the photocurrent.

[0077] In some specific embodiments, after the double-side film plating, the passivation anti-reflection layer is formed on the front and back surfaces, which comprises an AlO x thin film with a thickness of 8-10 nm, and a SiN x thin film with a thickness of 80-120 nm deposited on the AlO x thin film.

[0078] S12, screen printing, sintering, and light injection to obtain a TBC solar cell.

[0079] Specific embodiments and comparative examples.

[0080] Embodiment 1 This embodiment is prepared based on N-type monocrystalline silicon wafer, specifically, the preparation method of the TBC solar cell of this embodiment comprises the following steps: Step S1, pretreatment of the silicon wafer, including cutting and double-side polishing: select an N-type monocrystalline silicon wafer 2 after cutting by a diamond wire, as shown in Figure 2, the wafer after cutting has a cutting line mark 1 on one side, the thickness of the wafer after cutting is 150 μm, and the size is 182.2 mm x 186.7 mm. Put the wafer into an alkali polishing tank containing alkali liquor, and perform double-side polishing for 6 min, with the temperature maintained at 75℃, as shown in Figure 3, the polishing thickness removed after polishing is 4 μm, and the thinning amount is 0.42 g.

[0081] Step S2, deposit a tunneling SiO x layer and an i-poly-Si layer on the back surface of the polished wafer: as shown in Figure 4, a schematic diagram of the deposition of the tunneling SiO x layer and the i-poly-Si layer. On the back surface of the polished wafer, a tunneling SiO x layer 3 is grown by low-pressure chemical vapor deposition (LPCVD), with the gas flow of O2 being 40000 sccm, the temperature being 600℃, and the time being 600 s, and the thickness of the grown tunneling SiO x layer 3 being about 3 nm. After the growth of the tunneling SiO x layer 3, an i-poly-Si layer 4 is grown on the basis of the tunneling SiO x layer 3, with the gas flow of SiH4 being 920 sccm, the temperature being 550℃, the time being 3.3 h, and the working pressure being 300 mTorr, and the thickness of the grown i-poly-Si layer 4 being about 290 nm.

[0082] Step S3, pattern the surface of the i-poly-Si layer by ultraviolet laser to form a first oxidation barrier layer: after the p + -poly-Si layer region and the n + -poly-Si layer region on the surface of the i-poly-Si layer are designed, the surface of the i-poly-Si layer (the n + -poly-Si layer region) is patterned by an ultraviolet laser to form a dense first oxidation barrier layer, so as to block the entry of boron atoms into the region covered by the oxidation barrier layer in the subsequent boron diffusion process; the wavelength of the used ultraviolet laser is 355 nm, the power is 11 W, the tube-pass O2 flow is 50 sccm, the oxygen concentration in the environment is 25% (by volume), and the oxidation treatment time is 10 s, so as to form a patterned first oxidation barrier layer 5 with a thickness of about 50 nm on the surface of the i-poly-Si layer, as shown in Figure 5.

[0083] Step S4, boron diffusion in the region not protected by the first oxidation barrier layer: as shown in Fig. 6 is a schematic diagram after boron diffusion. The p + poly-Si layer 6, BCl3 and O2 mixed gas is introduced during boron diffusion, the temperature is 850°C, the diffusion time is 10 min, the gas flow of BCl3 is 200 sccm, and the gas flow of O2 is 1200 sccm. After the initial diffusion is completed, O2 is introduced again for oxidation promotion; the oxidation promotion temperature is 950°C, the gas flow of O2 is 7000 sccm, the promotion time is 30 min, and the formed BSG thickness is about 45 nm. Due to the presence of the first oxidation barrier layer, the p + poly-Si layer 6.

[0084] Step S5, removing the first oxidation barrier layer and the BSG layer: a chain etching machine is used to remove the BSG layer and the first oxidation barrier layer formed on the surface of the silicon wafer after boron diffusion, wherein the concentration of the hydrogen fluoride acid solution in the chain etching machine is 40wt%, and the belt speed is 3m / min. After removing the first oxidation barrier layer and the BSG layer, the back surface of the silicon wafer is the i-poly-Si layer and the p + poly-Si layer.

[0085] Step S6, ultraviolet laser secondary patterning oxidizes the p + poly-Si layer surface to form a second oxidation barrier layer: an ultraviolet laser is used to oxidize the surface of the p + poly-Si layer to form a dense second oxidation barrier layer on the surface, which is used to block the entry of phosphorus atoms in the subsequent phosphorus diffusion process; the region not forming the second oxidation barrier layer 7 is the region corresponding to the original first oxidation barrier layer, that is, the i-poly-Si layer not diffused by boron atoms in the previous step; the wavelength of the ultraviolet laser used is 355 nm, the power is 11 W, the O2 flow in the tube is 50 sccm, the oxygen concentration in the environment is 25% (volume ratio), and the oxidation treatment time is 10 s. The p + poly-Si layer surface forms a second oxidation barrier layer 7 with a thickness of about 50 nm, as shown in Fig. 7.

[0086] Step S7, phosphorus diffusion in the region not protected by the second oxidation barrier layer: as shown in Fig. 8 is a schematic diagram after phosphorus diffusion. The n + poly-Si layer region is formed by high-temperature phosphorus diffusion. +-poly-Si layer 8, when phosphorus diffusion, mixed gas of POCI3 and O2 is introduced, diffusion temperature is 790°C, diffusion time is 20 min, POCI3 is carried by nitrogen gas with flow rate of 1100 sccm, O2 gas flow rate is 700 sccm. After initial diffusion is completed, O2 is introduced again for oxidation promotion, oxidation promotion temperature is 890°C, O2 gas flow rate is 3000 sccm, promotion time is 40 min; PSG thickness is about 42 nm, due to existence of the second oxidation barrier layer, n + -poly-Si layer 8.

[0087] Step S8, removing wrap layer on the front side and side of the silicon wafer: after high temperature treatment, the silicon wafer is passed through a chain etching machine to remove the wrap layer on the front side and side of the silicon wafer, i.e. other generated n + -poly-Si layer / p + -poly-Si layer, volume ratio of hydrofluoric acid solution and nitric acid solution in the acid tank is 1:4 (hydrofluoric acid solution concentration is 49wt%, nitric acid solution concentration is 69wt%), tape speed is 1.3m / min.

[0088] Step S9, forming n + -poly-Si layer and p + Laser grooving at the junction of the n + -poly-Si layer and p + Laser grooving at the junction of the n

[0089] Step S10, double-sided texturing and removing the second oxidation barrier layer and PSG layer: as shown in FIG. 10, it is a schematic diagram of texturing. The silicon wafer after laser grooving is put into a texturing tank for texturing, wherein the concentration of KOH solution in the texturing tank is 1.7wt%, the temperature is maintained at 82°C, and the texturing time is 7 min. The thinning amount after texturing is 0.36g. Due to the fact that the wrap layer on the front side of the silicon wafer has been removed and the non-oxidation region exists, effective light-trapping texture can be formed during the texturing process, such as the pyramid texture 9 on the front side of the silicon wafer in FIG. 10. Subsequently, the subsequent acid (HF / HCl) cleaning tank after the texturing tank can further remove the residual PSG layer and the second oxidation barrier layer of the silicon wafer.

[0090] Step S11, double-sided film plating on the front and back of the silicon wafer to generate a passivation anti-reflection layer: ALD (atomic layer deposition) is adopted to first deposit AlOx Thin film, thickness 8nm, process temperature controlled at 250℃. Subsequently, SiN is deposited on both sides of the silicon wafer using a tube PECVD device x Thin film, SiN x The thickness of the thin film is about 90nm, and the refractive index is 2.0. SiN is deposited x The thin film is deposited by using SiH4 and NH3 as the reaction gas in the tube cavity, the working pressure is 1600mTorr, the power is 12000W, the temperature is 440℃, the flow rate of SiH4 gas is 980sccm, the flow rate of NH3 gas is 8000sccm, the silicon-nitrogen ratio is 1:5, and the deposition time is 10min.

[0091] Step S12, electrode layer is formed by screen printing + sintering + photo injection to obtain finished product battery: after the film is plated, the metal contact is formed on the back surface by screen printing, then sintering is performed at a temperature of 770℃ to form Ag-Si ohmic contact to form electrode layer, and finally photo injection is performed to repair to obtain final finished product battery.

[0092] As shown in Figure 1, the structure of the TBC solar cell after preparation is shown in the schematic diagram, the front surface of the silicon wafer is distributed with pyramid texturing 9, and the back surface of the silicon wafer is distributed with n + -poly-Si layer 8 and p + -poly-Si layer 6; n + -poly-Si layer 8 and p + -poly-Si layer 6 and silicon wafer There is a tunneling SiO x layer 3; adjacent n + -poly-Si layer 8 and p + -poly-Si layer 9 There is a gap between them, and there is also a pyramid texturing 9 at the gap. Each n + -poly-Si layer 8 or p + -poly-Si layer 6 corresponds to the Ag electrode in the electrode layer 12. The front surface passivation and anti-reflection layer 10 is plated on the pyramid texturing 9 on the front surface of the silicon wafer, and the back surface passivation and anti-reflection layer 11 is also plated on the back surface of the silicon wafer. In this embodiment, the n + -poly-Si layer 8 and p + -poly-Si layer 6 The height is basically the same, and there is no obvious height difference, which is beneficial to the preparation of the electrode layer by subsequent screen printing process and sintering, and improves the yield of the product.

[0093] In the present application, single i-poly-Si layer is combined with UV laser oxidation to form a mask for doping diffusion to obtain TBC solar cell. The whole preparation process only needs one i-poly-Si layer deposition and one laser grooving process. Compared with the existing technology of multiple deposition and grooving, the present application can reduce the problems of uneven thermal stress distribution caused by multiple polysilicon layer deposition, which leads to yield reduction and other problems. Meanwhile, the present application can reduce the damage of laser grooving to the silicon substrate. The present application can greatly reduce the amount of special gas and reduce the preparation cost compared with multiple deposition. In addition, compared with the existing technology of using single i-poly-Si layer, printing phosphorus paste and boron paste for drying and annealing to prepare the cell, the present application can not only avoid the performance degradation of the cell caused by the residue of phosphorus paste and boron paste on the silicon wafer (the cleaning of phosphorus paste and boron paste is difficult, and residue is usually generated), but also avoid the environmental pollution caused by the slurry in the production process (the present application can realize gas recovery, prevent air pollution, and can treat the recovered gas for reuse).

[0094] Example 2 The difference between example 2 and example 1 is only in S3 and S6, which adopts distributed differentiated violet light laser oxidation process: S3: first, under the conditions of O2 flow of 50 sccm, oxygen concentration of 25% (volume ratio) in the environment, UV laser wavelength of 355 nm, power of 11 W, and processing time of 10 s, generate a first oxidation barrier layer with a thickness of about 50 nm on the surface of the i-poly-Si layer region in the pre-set n + -poly-Si layer. Then, under the conditions of O2 flow of 200 sccm, oxygen concentration of 50% (volume ratio) in the environment, UV laser wavelength of 266 nm, power of 3 W, and processing time of 17 s, form a more dense first oxidation barrier layer.

[0095] S6: first, under the conditions of O2 flow of 50 sccm, oxygen concentration of 25% (volume ratio) in the environment, UV laser wavelength of 355 nm, power of 11 W, and processing time of 10 s, generate a second oxidation barrier layer with a thickness of about 50 nm on the surface of the i-poly-Si layer in the pre-set p + -poly-Si layer. Then, under the conditions of O2 flow of 200 sccm, oxygen concentration of 50% (volume ratio) in the environment, UV laser wavelength of 266 nm, power of 3 W, and processing time of 17 s, form a more dense second oxidation barrier layer.

[0096] Example 3 Step S1: select N-type single crystal silicon wafer cut by diamond wire, thickness of 150 μm, size of 182.2 mm x 186.7 mm. Put the silicon wafer into an alkali polishing tank, maintain the temperature at 75 ℃, and polish both sides for 6 min to obtain a polishing thickness of 4 μm and a thinning amount of 0.42 g.

[0097] Step S2: First, tunnel SiO₂ is grown on the polished silicon wafer surface using LPCVD. x Layer, O2 gas flow rate 40000 sccm, temperature 600℃, time 600s, the tunneled SiO2 grown x The layer thickness is 3nm; then tunneling SiO x An i-poly-Si layer is grown again on the basis of the first layer, wherein the SiH4 gas flow rate is 920 sccm, the temperature is 550℃, the time is 3.3h, the working gas pressure is 300mTorr, and the thickness of the i-poly-Si layer is approximately 290nm.

[0098] Step S3: Patterned oxidation is performed on the surface of the i-poly-Si layer using an ultraviolet laser to form a dense first oxide barrier layer on the patterned surface, which serves as a prerequisite for blocking the entry of boron atoms during the subsequent boron diffusion process. The ultraviolet laser used has a wavelength of 355nm, a power of 11W, an O2 flow rate of 50sccm, an oxygen concentration of 25% (volume ratio) in the environment, and a processing time of 10s, which can form a first oxide barrier layer with a thickness of about 50nm on the surface of the patterned i-poly-Si layer.

[0099] Step S4: Form p using a high-temperature boron diffusion method. + - Poly-Si layer, boron diffusion temperature 850℃, diffusion time 10 min, BCl3 gas flow rate 200 sccm, O2 gas flow rate 1200 sccm, oxidation advance temperature 950℃, O2 flow rate 7000 sccm, advance time 30 min, BSG layer thickness approximately 45 nm. Due to the presence of the first oxide barrier layer, p-type oxides can be formed at non-oxidized layer sites. + -poly-Si layer.

[0100] Step S5: Use a green picosecond laser to pattern the position of the first oxide barrier layer, so that the first oxide barrier layer is completely loosened. The laser wavelength used is 532nm, the frequency is 600KHz, the marking speed is 45000mm / s, the power is 50W, and the processing time is 3s.

[0101] Step S6: Next, wet alkaline cleaning is used on the laser-grooved areas to remove the first oxide barrier layer on the surface, exposing the bottom i-poly-Si layer. The temperature is 75℃, and the time is 180s. Because a BSG layer exists in the non-oxidized areas, it protects the bottom i-poly-Si layer during the wet cleaning process. + -The poly-Si layer is not damaged.

[0102] Step S7: Use high-temperature phosphorus diffusion method on non-p + -poly-Si layer region formation n +- poly-Si layer, phosphorus diffusion temperature 790°C, diffusion time 20 min, POCI3 carried by nitrogen flow rate 1100 seem, O2 flow rate 700 seem, oxidation push temperature 890°C, O2 flow 3000 seem, push time 40 min, PSG layer thickness about 42 nm, due to the presence of BSG layer can block phosphorus atoms diffusion into the bottom p + - poly-Si layer, prevent the layer from being inverted, and the non-BSG layer region can form n + - poly-Si layer.

[0103] Step S8, after high temperature treatment, the silicon wafer is removed through a chain etching machine to remove the front and four around the plated n + - poly-Si layer and p + - poly-Si layer region, where the volume ratio of hydrofluoric acid solution and nitric acid solution in the acid tank is 1:4 (hydrofluoric acid solution concentration is 49wt%, nitric acid solution concentration is 69wt%), tape speed 1.3m / min.

[0104] Step S9, then use picosecond laser to n + - poly-Si layer and p + - poly-Si layer interface laser grooving, n + - poly-Si layer and p + - poly-Si layer insulation isolation, laser wavelength 532nm, frequency 600KHZ, marking speed 45000mm / s, power 50W, processing time 3s.

[0105] Step S10, after laser grooving, the silicon wafer is put into a texturing tank for texturing, where the KOH solution concentration in the texturing tank is 1.7wt%, the temperature is maintained at 82°C, the texturing time is 7min, and the thinning amount is 0.36g. Due to the fact that the front side of the silicon wafer has been removed around the plated layer without oxidation region, effective light trapping texturing surface can be formed during the texturing process, and the back side without laser treatment region has PSG layer and BSG layer, which can effectively protect the region from being damaged during the texturing process. For the laser treated poly-Si layer region, further etching can be carried out during the texturing process, thereby forming an insulating Gap texturing region. Subsequently, the subsequent acid (HF / HCl) cleaning tank after the texturing tank can further remove the residual PSG layer and BSG layer of the silicon wafer.

[0106] Step S11, AlO x thin film generated by the reaction of Al(CH3)3 with water vapor, thickness 8nm, process temperature controlled at 250°C. Subsequently, SiN xThe film has a front-side SiNx film with a thickness of approximately 82 nm and a refractive index of 2.1; the back-side SiN... x The film thickness is approximately 90 nm, and the refractive index is 2.0. The reaction gases in the tubular cavity are SiH4 and NH3. The working pressure is 1600 mTorr, the power is 12000 W, the temperature is 440℃, the SiH4 gas flow rate is 980 sccm, the NH3 gas flow rate is 8000 sccm, the silicon-nitrogen ratio is 1:5, and the deposition time is 10 min.

[0107] Step S12: The coated sheet is screen-printed onto the back to form metal contacts, and then sintered at 770℃ to form Ag-Si ohmic contacts. Finally, it is repaired by light injection to obtain the final TBC battery.

[0108] Comparative Example 1 (using existing HPBC solar cells as a comparison): S1. A P-type monocrystalline silicon wafer cut with diamond wire was selected, with a thickness of 150 μm and dimensions of 182.2 mm × 186.7 mm. This silicon wafer was placed in an alkaline polishing bath containing alkaline solution, and the temperature was maintained at 75°C for 6 minutes for double-sided polishing. The polishing thickness was 4 μm, and the thinning amount was 0.42 g.

[0109] S2. LPCVD is used to grow tunneled SiO₂ on the polished silicon wafer surface. x In a layer where the O2 gas flow rate is 40,000 sccm, the temperature is 600℃, and the time is 600 s, tunneling SiO2 is grown. x The layer thickness is approximately 3 nm; then tunneling SiO x An i-poly-Si layer is grown again on the basis of the first layer, wherein the SiH4 gas flow rate is 920 sccm, the temperature is 550℃, the time is 1.5h, the working gas pressure is 300mTorr, and the thickness of the i-poly-Si layer is approximately 180nm.

[0110] S3. Using high-temperature phosphorus diffusion to transform the i-poly-Si layer into an n-poly-Si layer. + - Poly-Si layer, phosphorus diffusion temperature 790℃, diffusion time 15min, POCl3 carried by nitrogen at a flow rate of 1000sccm, O2 flow rate at 650sccm, oxidation propulsion temperature 890℃, O2 flow rate 3000sccm, propulsion time 20min, PSG layer thickness approximately 39nm.

[0111] S4, using picosecond laser in n + Patterned laser grooving was performed on a poly-Si layer. The laser wavelength was 532nm, the frequency was 600KHz, the marking speed was 45000mm / s, the power was 25W, and the processing time was 2.7s.

[0112] S5, the processed silicon wafer is passed through a chain etching machine to remove the front surface and the n around the periphery + - poly-Si layer, wherein the volume ratio of the hydrofluoric acid solution and the nitric acid solution in the acid tank is 1:4 (the concentration of the hydrofluoric acid solution is 49 wt%, and the concentration of the nitric acid solution is 69 wt%), and the tape speed is 1.6 m / min.

[0113] S6, the silicon wafer after laser grooving is placed in an alkali texturing tank for cleaning and texturing, wherein the concentration of the KOH solution is 1.7 wt%, the temperature is maintained at 80°C, the time is 7 min, and the thinning amount is 0.35 g; on the one hand, the back laser grooving area can be cleaned, so that the bottom p-type silicon substrate is exposed; on the other hand, an effective light trapping texturing surface can be formed on the front surface of the silicon wafer. Subsequently, the PSG layer remaining on the silicon wafer is further removed in a subsequent acid (HF / HCl) cleaning tank.

[0114] S7, an ALD deposition method is used to deposit AlO x thin film on the front and back surfaces of the processed silicon wafer, wherein the thin film is generated by the reaction of Al(CH3)3 with water vapor, and the process temperature is controlled at 250°C. Subsequently, a SiN x film is deposited on the front and back surfaces of the processed silicon wafer by a tube PECVD device, wherein the thickness of the SiN x thin film on the front surface is about 82 nm, and the refractive index is 2.1; the thickness of the SiN x thin film on the back surface is about 90 nm, and the refractive index is 2.0; the reaction gas in the tube cavity is SiH4 and NH3, the working pressure is 1600 mTorr, the power is 12000 W, the temperature is 440°C, the flow rate of SiH4 gas is 980 sccm, the flow rate of NH3 gas is 8000 sccm, the silicon-nitrogen ratio is 1:5, and the deposition time is 10 min.

[0115] S8, after the film-coated silicon wafer is passed through a screen printing machine, a metal contact is formed on the back surface, then sintering is performed at 750°C to form an Ag-Si ohmic contact, and finally a final product battery is obtained through photo injection repair.

[0116] Comparative Example 2 (using a two-time deposition poly-Si layer + two-time laser grooving process) S1, a N-type monocrystalline silicon wafer cut by a diamond wire is selected, the thickness is 150 μm, and the size is 182.2 mm x 186.7 mm. The cut silicon wafer is placed in an alkali polishing tank, the temperature is maintained at 75°C, and the time is 6 min for double-sided polishing, the polishing thickness is 4 μm, and the thinning amount is 0.42 g.

[0117] S2, subsequently, a tunneling SiO x layer is grown on the back surface of the polished silicon wafer by an LPCVD method, the gas flow rate of O2 is 40000 sccm, the temperature is 600°C, and the time is 600 s. xabout 3 nm; then a i-poly-Si layer is grown again on the basis of the tunneling SiO x layer, wherein the gas flow of SiH4 is 920 sccm, the temperature is 550 °C, the time is 3.3 h, the working pressure is 300 mTorr, and the thickness of the i-poly-Si layer is about 290 nm.

[0118] S3, the i-poly-Si layer is converted into a p + -poly-Si layer by high-temperature boron diffusion, the boron diffusion temperature is 850 °C, the diffusion time is 10 min, the gas flow of BCl3 is 200 sccm, the gas flow of O2 is 1200 sccm, the oxidation promoting temperature is 950 °C, the O2 flow is 7000 sccm, the promoting time is 30 min, and the thickness of the BSG layer is about 45 nm.

[0119] S4, the BSG layer is once patterned and slotted by a picosecond laser, the wavelength of the laser is 532 nm, the frequency is 600 KHZ, the marking speed is 45000 mm / s, the power is 50 W, and the processing time is 3 s.

[0120] S5, the silicon wafer after laser patterning and slotted is placed in an alkali solution for cleaning, the temperature is 75 °C, the time is 360 s, and the etching depth is 1.7 μm.

[0121] S6, a tunneling SiO x layer is grown again on the back surface of the silicon wafer by LPCVD, the gas flow of O2 is 30000 sccm, the temperature is 600 °C, the time is 450 s, and the thickness of the grown tunneling SiO x layer is about 2.5 nm; then a i-poly-Si layer is grown again on the basis of the tunneling SiO x layer, wherein the gas flow of SiH4 is 920 sccm, the temperature is 550 °C, the time is 1.5 h, the working pressure is 300 mTorr, and the thickness of the i-poly-Si layer is about 180 nm.

[0122] S7, an n + -poly-Si layer is formed in the i-poly-Si layer by phosphorus diffusion, the phosphorus diffusion temperature is 790 °C, the diffusion time is 15 min, the flow rate of POCl3 carried by nitrogen is 1000 sccm, the flow rate of O2 is 650 sccm, the oxidation promoting temperature is 890 °C, the O2 flow is 3000 sccm, the promoting time is 20 min, and the thickness of the PSG layer is about 39 nm.

[0123] S8, the PSG layer is twice patterned and slotted by a picosecond laser, so that the p + -poly bottom corresponds to the PSG layer and the p + -poly and the n+ The PSG layer at the poly boundary was loosened using a laser with a wavelength of 532nm, a frequency of 600KHz, a marking speed of 45000mm / s, a power of 25W, and a processing time of 2.7s.

[0124] S9. Using a chain machine, remove the n-plated coating from the front and side surfaces of the silicon wafer. + -poly-Si and p + -poly-Si layer, wherein the volume ratio of hydrofluoric acid solution and nitric acid solution in the acid bath is 1:4 (the concentration of hydrofluoric acid solution is 49wt%, and the concentration of nitric acid solution is 69wt%), and the belt speed is 1.3m / min.

[0125] S10. The silicon wafer with the de-coating removed is placed in an alkaline texturing tank for integrated wet cleaning of the back laser-grooved area and texturing of the front side. The KOH solution concentration in the texturing tank is 1.7wt%, the temperature is maintained at 82℃, and the time is 7 minutes, resulting in a weight loss of 0.36g. Since the front side of the silicon wafer has no oxide areas after the de-coating is removed, an effective light-trapping texture can be formed during the texturing process. On the back side, in the laser-patterned area, the alkaline solution can effectively etch the bottom poly-Si, forming an insulating structure. Subsequently, the texturing tank is followed by an acid (HF / HCl) cleaning tank to further remove any remaining PSG and BSG layers from the silicon wafer.

[0126] S11. AlO2 is deposited on the front and back sides of the processed silicon wafer using ALD deposition. x The thin film, formed by the reaction of Al(CH3)3 with water vapor, has a thickness of 8 nm and was processed at a temperature controlled at 250℃. Subsequently, SiN was deposited on both sides using a tubular PECVD apparatus. x Film, front-side SiN x The film thickness is approximately 82 nm, and the refractive index is 2.1; back side SiN x The film thickness is approximately 90 nm, and the refractive index is 2.0. The reaction gases in the tubular cavity are SiH4 and NH3. The working pressure is 1600 mTorr, the power is 12000 W, the temperature is 440℃, the SiH4 gas flow rate is 980 sccm, the NH3 gas flow rate is 8000 sccm, the silicon-nitrogen ratio is 1:5, and the deposition time is 10 min.

[0127] S12. The coated sheet is screen-printed onto the back to form metal contacts, and then sintered at 770℃ to form Ag-Si ohmic contacts. Finally, it is repaired by light injection to obtain the final TBC finished battery.

[0128] The electrical performance of the solar cells prepared in each embodiment and comparative example was tested, and the data are shown in the table below: From the data in the above table, it can be seen that the embodiments are obviously superior to the comparative examples in many performance data. Among them, the main difference between comparative example 2 and embodiment 1 is that the traditional twice deposition i-poly-Si and twice laser slotting process is adopted. The multiple i-poly-Si deposition is easy to cause uneven distribution of thermal stress, resulting in reduced product performance; at the same time, multiple laser slotting will increase the damage to the silicon wafer, thereby reducing V oc ; in addition, the multiple i-poly-Si deposition will also greatly increase the amount of special gas, increasing the production cost.

[0129] In addition, the difference between embodiment 2 and embodiment 1 is only that the distributed differential ultraviolet laser oxidation process is adopted. The oxide barrier layer formed by the conventional one-step ultraviolet laser oxidation process is often not ideal in density, which is easy to increase the risk of boron atoms and phosphorus atoms diffusing into the bottom i-poly-Si layer during the subsequent boron diffusion and phosphorus diffusion processes, thereby causing the battery performance to decline or to leak. The distributed differential ultraviolet laser oxidation process can make the oxide barrier layer more dense without increasing the thickness, so it can more effectively block the subsequent boron and phosphorus atom diffusion, thereby improving the battery performance.

[0130] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0131] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still falls within the protection scope of the technical solution of the present application.

Claims

1. A method for producing a TBC solar cell, characterized by The method comprises the following steps: S1, polishing both sides of a silicon wafer; S2, backside deposition tunneling SiO x layer, i-poly-Si layer; S3, forming a first oxidation barrier layer by one-time patterning of an i-poly-Si layer by ultraviolet laser; S4, boron diffusion, p in unoxidized region + - poly-Si layer and BSG layer; S5, removing the first oxidation barrier layer and the BSG layer; S6, UV laser secondary patterning oxidation p + - poly-Si layer, forming a second oxidation barrier layer; S7, phosphorous diffusion, n- in the region without the second oxidation barrier layer + - poly-Si layer and PSG layer; S8, removing the wrap-around plated layer; S9、in p + - poly-Si layer and n + - laser grooving at the poly-Si layer interface; S10, cleaning and texturing; S11, screen printing, sintering and light injection to obtain a TBC solar cell. In S3, the first oxidation barrier layer is formed by the following steps:

2. The method of claim 1, wherein: firstly, forming a 20-300nm first oxidation barrier layer under the conditions of 20-30% oxygen concentration and 300-400nm ultraviolet laser wavelength; secondly, forming a denser first oxidation barrier layer under the conditions of 30-80% oxygen concentration and 200-300nm ultraviolet laser wavelength. In S6, the second oxidation barrier layer is formed by the following steps:

3. The production method according to claim 1 or 2, characterized by: firstly, forming a 20-300nm second oxidation barrier layer under the conditions of 20-30% oxygen concentration and 300-400nm ultraviolet laser wavelength; secondly, forming a denser second oxidation barrier layer under the conditions of 30-80% oxygen concentration and 200-300nm ultraviolet laser wavelength. In S4, the boron diffusion process comprises the following steps:

4. The method of claim 1, wherein: In S2, deposited tunneled SiO x During the tunneling process, the O2 flow rate is 10,000–80,000 sccm, the reaction temperature is 400–800℃, and the time is 200–1000 s, tunneling SiO x The layer thickness is 2–10 nm.

5. The production method according to claim 1 or 4, characterized by: In S2, the i-poly-Si layer is deposited on the tunneling SiO x The gas flow of SiH4 is 300-2000 seem, the reaction temperature is 500-700 °C, the time is 2-4 h, the working pressure is 100-500 mTorr, and the thickness of the i-poly-Si layer is 100-300 nm.

6. The method of claim 1, wherein: firstly, passing a mixed gas of BCl3 and O2, the temperature is 800-950℃, the diffusion time is 5-50min, the BCl3 gas flow is 50-500sccm, and the O2 flow is 500-2000sccm; secondly, passing O2 for oxidation promotion, the temperature is 900-1050℃, the promotion time is 30-80min, the O2 flow is 5000-30000sccm, and a 30-70nm-thick BSG layer is formed. In S7, the phosphorus diffusion process comprises the following steps:

7. The method of claim 1, wherein: firstly, passing a mixed gas of POCl3 and O2, the temperature is 750-850℃, the diffusion time is 5-30min, the POCl3 flow carried by nitrogen is 500-1200sccm, and the oxygen flow is 500-1000sccm; secondly, passing O2 for oxidation promotion, the temperature is 850-950℃, the promotion time is 20-60min, the O2 flow is 1000-10000sccm, and a 30-70nm-thick PSG layer is formed. In S8, the step of removing the wrap-around plated layer on the front side and the side of the silicon wafer comprises the following step: removing the wrap-around plated layer on the front side and the side of the silicon wafer by using a chain etching machine.

8. The method of claim 1, wherein: In S9, the laser slotting conditions are as follows: the laser wavelength is 400-600nm, the frequency is 500-700KHz, the marking speed is 40000-50000mm / s, the power is 10-50W, and the processing time is 1-5s.

9. The method of claim 1, wherein: In S11, after the double-side film plating, a front side passivation anti-reflection layer is formed on the front side and a back side passivation anti-reflection layer is formed on the back side.

10. The method of claim 1, wherein: ​

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