Preparation process of low-cost back contact photovoltaic device

Abstract

The invention discloses a preparation process of a low-cost back contact photovoltaic device, and relates to the technical field of photovoltaics. According to the preparation process of the low-cost back contact photovoltaic device, a proper N-type silicon wafer is selected as a base material, the N-type silicon wafer is polished, a P + layer is formed on the surface of the N-type silicon wafer through boron diffusion, then single-side texturing is carried out, aluminum oxide and silicon nitride laminated film deposition is carried out, then laser treatment is carried out on one side, and acidity is carried out on the other side, so that the low-cost back contact photovoltaic device is obtained. Then forming a phosphorosilicate glass film and laser pattern interdigitated staggered pattern through laser, etching, opening an oxide layer in a P region on the back surface by adopting laser, finally printing aluminum paste in the P region, printing base metal paste in an N region, and sintering at the temperature of below 200 DEG C. According to the preparation process of the low-cost back contact photovoltaic device, the N region has no passivation dielectric film and only has a metal contact region, so that the process is greatly simplified, the metallization of the back N region can be realized by adopting base metal low-temperature slurry, the overall realization and low-temperature metallization are realized, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaics, and specifically to a preparation process for a low-cost back-contact photovoltaic device. Background Art

[0002] A back-contact battery is a battery structure in which both the positive and negative electrodes are on the back and there are no grid lines on the front. Generally, the battery has a relatively high conversion efficiency, but it has many process steps, high difficulty, and relatively high costs, which to a certain extent limit its development. The main reasons for the high cost of back-contact batteries are one is the complex process steps, and another important reason is that its metallized electrodes consume precious metal silver.

[0003] There are many types of back-contact battery structures. Which structure design can be industrialized depends on its cost and conversion efficiency. Different structure designs have quite different process complexities and achieved efficiencies. The industrialized back-contact batteries include those based on N-type silicon wafers, with metallization achieved by electroplating process, and both the positive and negative electrodes are passivated by contact, with relatively high costs, and some of them require low-temperature silver paste, with relatively high costs and complex process flows; another type is the back-contact battery based on P-type silicon wafers. Since the positive electrode uses aluminum paste, the cost is relatively low, and the efficiency is comparable to that of current mainstream N-type batteries such as N-TOPCon and HJT batteries. It is difficult to further improve the efficiency. The present invention proposes a preparation process for a high-efficiency N-type back-contact battery, with a simple process flow, no passivation dielectric film region in the N region, metallization, low cost, and high efficiency. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a preparation process for a low-cost back-contact photovoltaic device, which solves the problems of the existing back-contact batteries, which use electroplating process for metallization, both the positive and negative electrodes are passivated by contact, with relatively high costs, and it is difficult to improve the efficiency.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A preparation process for a low-cost back-contact photovoltaic device includes the following steps;

[0006] Step 1: Select an N-type silicon wafer with a resistivity of 0.3 - 100 Ω·cm and perform double-sided polishing treatment;

[0007] Step 2: Perform boron diffusion on the silicon wafer in a high-temperature furnace tube through a gaseous boron diffusion source to form a p+ layer;

[0008] Step 3: Perform single-sided texturing on the non-boron-diffused surface of the N-type silicon wafer, and simultaneously perform double-sided cleaning to remove the boron-containing silicon dioxide glass film on the back;

[0009] Step 4: Deposit a stacked film of aluminum oxide and silicon nitride on both sides of the N-type silicon wafer;

[0010] Step 5: Perform laser patterning on the backside of the N-type silicon wafer, with the laser area being the N-type region;

[0011] Step 6: In a chain equipment, perform backside dipping of the N-type silicon wafer in a low-concentration acidic solution, and protect the front side with a water film;

[0012] Step 7: Laser the backside of the silicon wafer, deposit phosphorus on the surface of the single-crystalline silicon in the N region to form a phosphosilicate glass film, leaving the single-crystalline silicon in the N region with a width of 30 - 200 um unlasered and a spacing of 500 - 1000 um wide, forming an interdigitated pattern of the phosphosilicate glass film and the laser pattern, and then etch the lasered single-crystalline silicon region in an alkaline solution;

[0013] Step 8: For the backside P region, use a laser to open the alumina and silicon nitride films;

[0014] Step 9: Print aluminum paste on the P region and print base metal paste on the N region, and sinter at a temperature below 200 °C.

[0015] Preferably, the process of double-sided polishing the N-type silicon wafer in Step 1 is as follows;

[0016] 1. Pretreatment: Remove organic contaminants, particles, and metal impurities on the surface of the silicon wafer through RCA cleaning, and then remove the mechanical damage layer on the surface of the silicon wafer through grinding;

[0017] 2. Rough polishing: Use silica as abrasive particles to perform mechanical grinding on both sides of the silicon wafer under pressure and rotation;

[0018] 3. Use a chemical mechanical polishing solution to perform low-speed and low-pressure grinding and polishing on both sides of the silicon wafer;

[0019] 4. Perform ultrasonic cleaning by adding ionized water to an ultrasonic cleaner;

[0020] 5. Use an optical microscope to inspect the surface roughness, flatness, and defects of the silicon wafer.

[0021] Preferably, the gaseous boron diffusion source in Step 2 uses boron tribromide or boron trichloride.

[0022] Preferably, the specific implementation process of boron diffusion in Step 2 is as follows;

[0023] 1. Pre-oxidation: Introduce water vapor into a high-temperature furnace tube, place the cleaned silicon wafer, and grow an oxide layer on the surface of the silicon wafer at 800 °C - 1100 °C;

[0024] 2. Coating of boron source: Heat and evaporate liquid boron tribromide, use nitrogen as a carrier gas, introduce it into the furnace tube, and form a doping source on the surface of the silicon wafer;

[0025] III. High-temperature diffusion: Set the high-temperature furnace tube at 900°C to 1100°C, and use the carrier gas as the protective atmosphere to diffuse the silicon wafer.

[0026] IV. Implantation: Use nitrogen as the carrier gas and directly introduce gaseous boron trichloride to further adjust the distribution of boron atoms and form a more uniform doping layer.

[0027] V. Removal of oxide layer: Remove the silicon wafer and use hydrofluoric acid solution for wet etching to remove the oxide layer.

[0028] Preferably, in the single-sided texturing process in Step III, dry etching is used, and plasma etching is used to form a nanoscale textured surface on the silicon wafer surface.

[0029] Preferably, in the deposition process of the alumina and silicon nitride stacked film in Step IV, plasma-enhanced chemical vapor deposition is used. After deposition, annealing is carried out with nitrogen as the atmosphere, and the annealing temperature is controlled at 400°C to 450°C, and the annealing time is controlled at 15 to 30 minutes.

[0030] Preferably, in Step VII, the deposition process of the phosphosilicate glass thin film uses the thermal diffusion method, and liquid phosphorus source phosphorus oxychloride is used to diffuse phosphorus atoms at 800°C to 1000°C to form it.

[0031] Preferably, in Step VIII, the P region is scanned with an ultraviolet laser beam, and by precisely controlling the laser energy, the alumina and silicon nitride films are locally ablated without damaging the silicon wafer.

[0032] Preferably, in Step IX, the base metal paste is a copper alloy paste.

[0033] Preferably, in Step IX, the base metal paste is tin bismuth.

[0034] The present invention discloses a preparation process for a low-cost back-contact photovoltaic device, and its beneficial effects are as follows:

[0035] 1. In this preparation process for a low-cost back-contact photovoltaic device, there is no passivation dielectric film in the N region, which greatly simplifies the process.

[0036] 2. For the metallization of the back N region, since there is no passivation dielectric film and the N region is heavily doped n+-poly, base metal low-temperature paste can be used.

[0037] 3. The P region is a heavily doped p+ layer, and low-temperature aluminum paste can be used; laser-assisted sintering can also be used.

[0038] 4. Overall, low-temperature metallization is achieved, and the cost is low. Description of the Drawings

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0040] Figure 1 This is the overall process flow chart of the present invention;

[0041] Figure 2 This is a schematic diagram of the surface structure of the silicon wafer of the present invention;

[0042] Figure 3 This is the process flow chart for double-sided polishing treatment of the N-type silicon wafer of the present invention;

[0043] Figure 4 This is the specific implementation process flow chart of boron diffusion of the present invention. Specific implementation manners

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0045] The embodiments of the present application provide a preparation process for a low-cost back-contact photovoltaic device, which solves the problems of the existing back-contact battery, which uses an electroplating process during metallization, both the positive and negative electrodes use contact passivation, the cost is relatively high, and it is difficult to improve the efficiency.

[0046] To better understand the above technical solutions, the following will describe the above technical solutions in detail in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0047] The embodiments of the present invention disclose a preparation process for a low-cost back-contact photovoltaic device.

[0048] According to the attached Figures 1-4 As shown, the following steps are included;

[0049] Step 1: Select an N-type silicon wafer with a resistivity of 0.3 to 100 Ω·cm and perform double-sided polishing treatment. This process strictly follows the following steps;

[0050] I. Pretreatment: Remove organic contaminants, particles, and metal impurities on the surface of the silicon wafer through RCA cleaning, and then remove the mechanical damage layer on the surface of the silicon wafer through grinding;

[0051] II. Coarse polishing: Mechanically grind both sides of the silicon wafer using silicon dioxide as abrasive particles under pressure and rotation.

[0052] III. Use chemical mechanical polishing fluid to perform low-speed and low-pressure grinding and polishing on both sides of the silicon wafer.

[0053] IV. Perform ultrasonic cleaning by adding ionized water to an ultrasonic cleaner.

[0054] V. Use an optical microscope to inspect the surface roughness, flatness, and defects of the silicon wafer.

[0055] In this step, the surface of the substrate silicon wafer is treated through strict processing steps to make its surface smoothness, flatness, and integrity meet the requirements of subsequent processes, avoiding the situation of finished product scrapping due to substrate defects during subsequent processing.

[0056] Step II: Perform boron diffusion on the silicon wafer in a high-temperature furnace tube through a gaseous boron diffusion source to form a p+ layer. The gaseous boron diffusion source can use boron tribromide and boron trichloride. The whole process is as follows:

[0057] I. Pre-oxidation: Introduce water vapor into the high-temperature furnace tube, place the cleaned silicon wafer, and make an oxide layer grow on the silicon wafer surface at 800°C - 1100°C.

[0058] II. Coating boron source: Heat and evaporate liquid boron tribromide, use nitrogen as a carrier gas, introduce it into the furnace tube, and make it form a doping source on the silicon wafer surface.

[0059] III. High-temperature diffusion: Set the high-temperature furnace tube to 900°C - 1100°C, use the carrier gas as a protective atmosphere, and make the silicon wafer diffuse.

[0060] IV. Driving in: Use nitrogen as a carrier gas and directly introduce gaseous boron trichloride to further adjust the distribution of boron atoms and form a more uniform doping layer.

[0061] V. Oxide layer removal: Remove the silicon wafer and use hydrofluoric acid solution for wet etching to remove the oxide layer.

[0062] After the P+ layer treatment is completed, measure the resistance value of the entire thin layer through the four-probe method, and then use secondary ion mass spectrometry to analyze the concentration distribution of boron atoms to ensure that the unit density of boron atoms in the entire P+ layer meets the process requirements, and the uniformity meets the conductive requirements, avoiding abnormal resistance caused by excessive local deviation values.

[0063] Step III: Perform single-sided texturing on the non-boron-diffused surface of the N-type silicon wafer. The single-sided texturing process uses dry etching, uses plasma etching to form a nanoscale textured surface structure on the silicon wafer surface, and at the same time performs double-sided cleaning to remove the boron-containing silicon dioxide glass film on the back.

[0064] Through the process of forming a textured structure on the surface of the silicon wafer, it is mainly used to reduce light reflection and improve light absorption efficiency. After the texturing is completed, the surface morphology of the texture is observed through an optical microscope to analyze the details of the texture structure, and a spectrophotometer is used for reflectivity testing to measure the surface reflectivity.

[0065] Step 4: Deposit a stacked film of alumina and silicon nitride on both sides of the N-type silicon wafer. During the entire process of depositing the stacked film of alumina and silicon nitride, plasma-enhanced chemical vapor deposition is used. After the deposition is completed, annealing is carried out with nitrogen as the atmosphere, and the annealing temperature is controlled at 400 °C to 450 °C, and the annealing time is controlled at 15 to 30 minutes.

[0066] Step 5: Perform laser patterning on the back of the N-type silicon wafer. The laser area is the N-type region. During this process, first ensure that the passivation layer such as alumina Al2O3 and the covering layer such as silicon nitride SiN deposited on the back of the silicon wafer are intact. Then, select the appropriate laser type, power, spot size, and scanning speed according to the process requirements. Next, use the laser to locally ablate the passivation layer and the covering layer on the back to form a specific pattern. Then, remove the residues generated by the laser ablation. Then, perform local doping or metallization contact in the area where the laser is turned on. Finally, perform annealing treatment to activate the doped atoms or improve the metal contact performance, and use an optical microscope to verify the laser patterning quality and local contact performance. x Step 6: In a chain-type device, perform backside low-concentration acidic solution dipping on the N-type silicon wafer, and protect the front side with a water film.

[0067] During the pickling process, first use 1% to 3% hydrofluoric acid to remove the oxide layer, then use 1% to 4% hydrochloric acid to remove metal impurities, and finally use the acid solution before and after to form a mixed acid with a concentration controlled at 1% to 2% to roughen and clean its surface. The entire pickling process is controlled within 45 seconds to avoid over-corrosion.

[0068] Step 7: Laser the back of the silicon wafer, deposit phosphorus on the surface of the single-crystalline silicon in the N region to form a phosphosilicate glass film. The entire process of depositing the phosphosilicate glass film uses the thermal diffusion method, and uses the liquid phosphorus source phosphorus oxychloride to diffuse phosphorus atoms at 800 °C to 1000 °C to form it. Leave the single-crystalline silicon in the N region with a width of 30 - 200 um and a spacing of 500 - 1000 um without laser treatment to form an interdigitated pattern of the phosphosilicate glass film and the laser pattern. Subsequently, etch the laser-treated single-crystalline silicon region in an alkaline solution.

[0069] Step 8: For the back P region, use a laser to open the alumina and silicon nitride films, scan the P region with an ultraviolet laser beam, and precisely control the laser energy to locally ablate the alumina and silicon nitride films without damaging the silicon wafer.

[0070]

[0071] ​Step 9: Print aluminum paste in the P region and print base metal paste in the N region. The base metal paste is tin paste or tin-bismuth, and sinter at a temperature below 200 degrees Celsius.

[0072] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A low-cost back-contact photovoltaic device preparation process, characterized in that: The steps include: Step 1, select an N-type silicon wafer with a resistivity of 0.3 to 100 Ω.cm and perform double-sided polishing; Step 2: Boron is diffused into the silicon wafer in a high-temperature furnace tube through a gas-phase boron diffusion source to form a p+ layer; Step 3: Texturing the non-boron diffusion surface of the N-type silicon wafer on one side and cleaning both sides at the same time to remove the boron-containing silicon dioxide glass film on the back side; Step 4: Depositing aluminum oxide and silicon nitride stacked films on both sides of the N-type silicon wafer; Step 5: Laser patterning the back of the N-type silicon wafer, with the laser area being the N-type area; Step 6: In the chain equipment, the back side of the N-type silicon wafer is cleaned with a low-concentration acid solution, and the front side is protected with a water film; Step 7: Laser the back of the silicon wafer, and deposit phosphorus on the surface of the single crystal silicon in the N region to form a phosphorus-silicon glass film, leaving the N region single crystal silicon with a width of 30-200um and a spacing of 500-1000um un-lased, forming a phosphorus-silicon glass film and laser pattern interdigitated pattern, and then etching the single crystal silicon area with the laser in an alkaline solution; Step 8: In the back P region, the aluminum oxide and silicon nitride films are opened by laser; Step 9: Print aluminum paste in the P area and base metal paste in the N area, and sinter at below 200 degrees.

2. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: The process of double-sided polishing of the N-type silicon wafer in step 1 is as follows:

1. Pre-treatment: RCA cleaning is used to remove organic pollutants, particles and metal impurities on the surface of the silicon wafer, and then the mechanical damage layer on the surface of the silicon wafer is removed by grinding; 2. Rough polishing: using silicon dioxide as abrasive particles to mechanically grind both sides of the silicon wafer under pressure and rotation; 3. Use chemical mechanical polishing liquid to perform low-speed and low-pressure double-sided grinding and polishing of silicon wafers; Fourth, ultrasonic cleaning is performed by adding ionized water to an ultrasonic cleaning machine; 5. Use an optical microscope to inspect the surface roughness, flatness and defects of the silicon wafer.

3. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: The gas phase boron diffusion source in step 2 is boron tribromide and boron trichloride.

4. A low-cost back-contact photovoltaic device preparation process according to claim 3, characterized in that: The specific implementation process of the boron diffusion in step 2 is as follows:

1. Pre-oxidation: water vapor is introduced into a high-temperature furnace tube, and the cleaned silicon wafer is placed in it, so that an oxide layer grows on the surface of the silicon wafer at 800℃~1100℃; 2. Coating the boron source, heating and evaporating the liquid boron tribromide, and introducing it into the furnace tube with nitrogen as the carrier gas to form a doping source on the surface of the silicon wafer; 3. High temperature diffusion: Set the high temperature furnace tube to 900℃~1100℃, use carrier gas as protective atmosphere to make the silicon wafer diffuse; Fourth, driving in, using nitrogen as a carrier gas, directly introducing gaseous boron trichloride, thereby further adjusting the distribution of boron atoms to form a more uniform doping layer; 5. Removal of oxide layer: remove the silicon wafer and use hydrofluoric acid solution to wet etch and remove the oxide layer.

5. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: The single-sided texturing process in step three adopts dry etching and plasma etching to form a nano-scale texturing structure on the surface of the silicon wafer.

6. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: In the step 4, the deposition process of the aluminum oxide and silicon nitride stacked film adopts plasma enhanced chemical vapor deposition, and after the deposition is completed, annealing is performed using nitrogen as the atmosphere, the annealing temperature is controlled at 400°C to 450°C, and the annealing time is controlled at 15 to 30 minutes.

7. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: In the step seven, the deposition process of the phosphosilicate glass film adopts a thermal diffusion method, using a liquid phosphorus source, phosphorus oxychloride, to diffuse phosphorus atoms at 800° C. to 1000° C.

8. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: In the step eight, an ultraviolet laser beam is used to scan the P region, and the aluminum oxide and silicon nitride films are locally ablated by precisely controlling the laser energy without damaging the silicon wafer.

9. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: In the step nine, the base metal slurry is a copper alloy slurry such as tin-clad copper.

10. A low-cost back-contact photovoltaic device preparation process according to claim 1, characterized in that: In the step nine, the base metal slurry is pure tin or tin alloy slurry, such as tin-bismuth, tin-silver-bismuth, tin-lead-bismuth and other low-temperature tin alloy slurries.

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