Topcon solar cell and preparation method therefor

Abstract

The present application belongs to the technical field of solar cells, and specifically relates to a TOPCon solar cell and a preparation method therefor. In the present application, a tunnel oxide layer is deposited by means of a combination of PECVD and PEALD. A thin oxide layer with a thickness of 0.1-0.5 nm is pre-deposited by means of PECVD, wherein in a subsequent PEALD process, the thin oxide layer chemically passivates a surface of a substrate, and then the PEALD process is used to uniformly deposit a tunnel oxide layer on the basis of the oxide layer. The basic principle of such growth mode is atomic layer deposition, the uniformity of the oxide layer is good, and the influence of an airflow, temperature, electric field and radio frequency in a tube is relatively small; therefore, electroluminescence test defects such as dark spots caused by producing the tunnel oxide layer completely by means of nitrous oxide ionization can be avoided, and the influence of damage of plasma bombardment to the surface of a substrate can be reduced, thereby improving to a certain extent the conversion efficiency of the TOPCon solar cell.

Description

A TOPCon solar cell and its preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on October 16, 2023, with application number 202311334473.0 and invention name “A TOPCon solar cell and its preparation method”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of solar cells, and specifically relates to a TOPCon solar cell and a preparation method thereof. Background Art

[0004] High-efficiency crystalline silicon solar cells - Tunnel Oxide Passivated Contact solar cells (TOPCon) are a new type of silicon solar cell proposed by the Fraunhofer Institute for Solar Energy in Germany in recent years. This cell uses a high-quality ultra-thin silicon oxide-doped polysilicon layer to achieve high-efficiency passivation and selective carrier collection on the entire back side of the cell.

[0005] In the field of crystalline silicon solar cells, tunneling oxide passivation contact (TOPCon) technology is an excellent cell passivation technology. In TOPCon cells, a passivation contact layer composed of a tunneling oxide layer and a polysilicon layer is deposited on the back of the cell. This layer can passivate the metal contact area on the back of the cell, reducing the recombination of photogenerated carriers in the metal contact area on the back of the cell, thereby improving cell performance.

[0006] In the existing technology, plasma-enhanced chemical vapor deposition (PECVD) technology is usually used to produce the tunneling oxide layer on the back of the TOPCon battery. However, the direct use of nitrous oxide ionization to deposit the tunneling oxide layer has the following defects: for the tunneling oxide layer to continue to grow thicker, oxygen elements need to pass through the grown oxide layer to the interior of the substrate (silicon wafer) and continue to react with silicon. Due to the influence of the airflow, temperature, electric field and radio frequency in the tube during the deposition process, the tunneling oxide layer deposited by PECVD has poor uniformity; the bombardment of the substrate surface by plasma causes damage to the substrate surface.

[0007] In view of this, it is necessary to provide a method for preparing a TOPCon solar cell that can improve the uniformity of the tunneling oxide layer and avoid damage to the substrate surface.

[0008] Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present application is to overcome the defects of poor uniformity of the tunneling oxide layer and damage to the substrate surface in the preparation of TOPCon solar cells in the prior art, thereby providing a TOPCon solar cell and a preparation method thereof.

[0010] To this end, this application provides the following technical solutions:

[0011] The present application provides a method for preparing a TOPCon solar cell, including a tunneling oxide layer. The method for preparing the tunneling oxide layer includes the following steps: depositing a first oxide layer on the surface of a substrate by plasma-enhanced chemical vapor deposition, and depositing a second oxide layer by plasma-enhanced atomic deposition, wherein the thickness of the first oxide layer is 0.1-0.5 nm.

[0012] In this application, there is no particular limitation on the composition of the tunnel oxide layer. The material is usually silicon dioxide, but it can also be silicon oxynitride, but it is not mainstream.

[0013] Optionally, the thickness of the first oxide layer is 0.1-0.2 nm.

[0014] Optionally, the second oxide layer has a thickness of 0.3-2 nm.

[0015] Optionally, the method for preparing the TOPCon solar cell comprises the following steps:

[0016] S1, texturing, diffusion and alkali polishing of the substrate;

[0017] S2, depositing tunnel oxide layer;

[0018] S3, depositing an intrinsic amorphous silicon layer;

[0019] S4, depositing a doped amorphous silicon layer;

[0020] S5, deposition of a silicon dioxide layer;

[0021] S6, annealing, wet process, atomic layer deposition, coating, front and back electrode printing, sintering.

[0022] Among them, steps S2-S5 are all formed on the back side of the substrate; step S1 is texturing the entire substrate, diffusion is performed on the front side, and alkali polishing generally only processes the back side. The specific operations of the texturing, diffusion, alkali polishing, wet processing, atomic layer deposition, coating, front and back electrode printing steps in this application, as well as the operating parameters of steps S2-S5, are all conventional in the field and are not specifically limited here.

[0023] Optionally, in step S3, the intrinsic amorphous silicon layer is deposited using plasma enhanced chemical vapor deposition technology;

[0024] And / or, the thickness of the intrinsic amorphous silicon layer is 10-20 nm.

[0025] Optionally, in step S4, a plasma enhanced chemical vapor deposition technique is used to deposit the doped amorphous silicon layer;

[0026] And / or, the thickness of the doped amorphous silicon layer is 20-130 nm;

[0027] And / or, the doped amorphous silicon layer is composed of a phosphorus-doped amorphous silicon layer.

[0028] Optionally, in step S5, a silicon dioxide layer is deposited using plasma enhanced chemical vapor deposition technology;

[0029] And / or, the thickness of the silicon dioxide layer is 10-15 nm.

[0030] Optionally, in step S1, the texturing step is performed by forming a velvet shape on the surface of the substrate by alkali etching;

[0031] And / or, the diffusion step is performed by doping boron element on the front surface of the substrate;

[0032] And / or, the alkali polishing step is performed to form a polished surface on the back side of the substrate.

[0033] Optionally, in step S6, the wet process is performed to remove the doped amorphous silicon layer at the edge of the substrate and the phosphosilicate glass layer on the back surface of the substrate;

[0034] And / or, the atomic layer deposition step is performed by depositing an aluminum oxide passivation layer on the front surface of the substrate;

[0035] And / or, the coating step is performed by coating a silicon nitride anti-reflection layer on the front and back sides of the substrate.

[0036] And / or, the sintering temperature is 650-850° C., and the sintering time is 1-2 minutes.

[0037] The present application also provides a TOPCon solar cell prepared by the above-mentioned preparation method.

[0038] The operating parameters in the preparation process of each functional layer in this application are conventional in the field. Typically, but not limiting, the operating parameters for depositing the first oxide layer may include: nitrous oxide flow rate of 8000-10000sccm, power of 8000-10000W, and deposition time of 15-30s.

[0039] The operating parameters for depositing the second oxide layer may include: a total flow rate of argon carrying the silicon source of 2000-2500 sccm, a nitrous oxide flow rate of 2000-2500 sccm, a deposition time of 1-2 minutes, and a power of 6000-9000W.

[0040] The intrinsic amorphous silicon layer thin film is deposited by introducing a mixed gas of argon and silane, the RF power is 8000-11000W, the deposition temperature is 400-450℃, the process pressure is 300-360Pa, the deposition time is 4-8min, the argon flow rate is 6000-8000sccm, the silane flow rate is 2000-2500sccm, and the film thickness is controlled at 10-20nm.

[0041] Deposit the doped amorphous silicon layer thin film, introduce a mixed gas of argon, silane and phosphine, the RF power is 8000-10000W, the deposition temperature is 400-450℃, the process pressure is 300-360Pa, the deposition time is 20-30min, the argon flow rate is 6000-8000sccm, the silane flow rate is 1500-2000sccm, the phosphine flow rate is 2500-3000sccm, and the film thickness is controlled at 20-130nm.

[0042] To deposit a silicon dioxide film, a mixed gas of silane and nitrous oxide is introduced, the RF power is 8000-10000W, the deposition temperature is 400-450℃, the process pressure is 200-240Pa, the deposition time is 1-2min, the silane flow rate is 2500-3000sccm, the nitrous oxide flow rate is 6000-8000sccm, and the film thickness is controlled at 10-15nm.

[0043] The technical solution of this application has the following advantages:

[0044] The preparation method of TOPCon solar cells provided in the present application changes the method of depositing the tunnel oxide layer entirely by nitrous oxide ionization to a method combining plasma enhanced chemical vapor deposition (PECVD) + plasma enhanced atomic deposition (PEALD) to deposit the tunnel oxide layer. In the subsequent PEALD process, the grown first oxide layer plays a role of chemical passivation on the surface of the substrate, and then a second oxide layer is uniformly deposited on the basis of the oxide layer using the PEALD process. The basic principle of this growth method is atomic layer deposition. The oxide layer has good uniformity and is less affected by the airflow, temperature, electric field, and radio frequency in the tube. It can avoid poor electroluminescence (EL) tests such as stuck points and other defects caused by the tunnel oxide layer produced entirely by nitrous oxide ionization, and reduce the damage caused by plasma bombardment on the substrate surface, thereby improving the conversion efficiency of TOPCon solar cells to a certain extent.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the accompanying drawings, in which:

[0047] FIG1 is an example of data obtained by observing a tunnel oxide layer cross section using a scanning electron microscope (SEM) and calculating uniformity. DETAILED DESCRIPTION

[0048] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0049] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0050] PECVD technology uses an external electric field to act on the reacting gases, ionizing them and producing a glow discharge effect. In this application, radio frequency methods are used to generate plasma formed by the glow discharge of nitrous oxide. Through high-energy plasma activation, the plasma reacts with the substrate silicon to form the required oxide layer.

[0051] PEALD technology introduces a plasma source on the basis of traditional ALD (atomic layer deposition). In the specific implementation of this application, an oxygen source such as nitrous oxide or oxygen (this application takes nitrous oxide as an example) is used as a plasma source. Under the activation of the plasma, the nitrous oxide reacts with the alternately introduced silicon source to generate an oxide layer. The oxygen element in the oxide layer comes from the ionization of the introduced nitrous oxide, and the silicon element comes from the silicon source.

[0052] In the specific scheme given in the embodiment of the present application, the oxygen element in the first oxide layer deposited by PECVD comes from the ionization of the introduced nitrous oxide, and the silicon element comes from the substrate silicon. Through the scheme of surface Si-based oxidation, the oxide layer grows inward. The formed first oxide layer can smooth the surface of the substrate silicon, simultaneously clean the surface, and compositely passivate internal defects, thereby providing a high-quality c-Si / SiOx interface.

[0053] However, directly adopting the PECVD laughing gas ionization mode to continue to deposit the tunneling oxide layer (i.e. the second oxide layer) has the following defect: the oxide layer growth is seriously affected by the surface state, and because the accumulated oxide layer thickens gradually, it is necessary for the oxygen element to continue to react with silicon inside the substrate through the grown silicon oxide layer, and the generated oxide layer blocks the oxygen free radical from diffusing to the Si base, and the growth rate gradually decreases until saturation, and the oxide layer thickness cannot be accurately controlled, which is the biggest shortcoming of PECVD making the oxide layer. And due to the influence of air flow, temperature, electric field, radio frequency in the tube during deposition, the tunneling oxide layer deposited by PECVD has poor uniformity, which can not realize the good uniformity of the application. In this case, the tunneling oxide layer SiO2 is prone to poor uniformity in the chip, and the batch-to-batch difference is large, and the problems in the actual application processes such as poor passivation effect are also present. In addition, there is also the problem that the bombardment of the substrate surface by plasma causes damage to the substrate surface.

[0054] In the specific solution given in the examples of this application, the second oxide layer is grown using PEALD technology. The oxygen element in the second oxide layer grown using PEALD technology comes from the ionization of the introduced nitrous oxide, and the silicon element comes from the silicon source. During the PEALD reaction, plasma is only generated when nitrous oxide is introduced, and no ionization occurs when the silicon source is introduced, thereby reducing the damage to the substrate surface caused by the plasma. In addition, PEALD technology retains the self-limiting reaction of ALD, deposits in atomic layers, has excellent thickness control and uniformity, and solves the requirement for precise control of the atomic-level thickness required for tunneling in the tunnel oxide layer.

[0055] However, if PEALD is used to prepare the first oxide layer, the principle of PEALD is to ionize nitrous oxide to produce oxygen anions, which react with silicon that is introduced into the silicon source and chemically adsorbed on the surface of the substrate to generate silicon oxide. The Si on the surface of the substrate is not consumed, and there are many interface defects. There is no process of forming a silicon oxide layer from the defective Si, and the passivation effect of PECVD on the inner side cannot be achieved. In addition, the Si on the surface of the substrate is not consumed, and the effect of PECVD on smoothing the silicon-based surface on the inner side cannot be achieved. The quality and uniformity of the generated silicon oxide layer are not as good as those of PECVD on the inner side. Taking Comparative Example 3 described below as an example, the tunneling oxide layer only grew a 0.9nm second oxide layer prepared by PEALD, without a 0.1nm first oxide layer grown by PECVD. This directly led to poor uniformity of the overall tunneling oxide layer. The main reason was that the surface roughness layer did not grow an epitaxial oxide layer, resulting in a rough and uneven interface. This directly led to the subsequent PEALD atomic layer oxide growth, resulting in poor atomic saturation coverage, unstable periodic growth rate, and island-like growth, ultimately leading to poor uniformity. In fact, film thickness uniformity depends on the state of the initial interface, such as the substrate surface roughness.

[0056] In addition, if PEALD is used to grow the first oxide layer and then PECVD is used to prepare the second oxide layer, due to the blocking effect of the first oxide layer, when PECVD is used to prepare the second oxide layer, oxygen free radicals cannot diffuse to the surface of the Si substrate, and SiO2 growth is extremely difficult, and the technical effect of the present application cannot be achieved. If the oxide layer prepared by PECVD is not on the inner layer but on the outer layer, that is, PECVD is used to prepare the second oxide layer instead of the first oxide layer, the PECVD technology described in the background technology of this application directly uses nitrous oxide ionization to deposit the tunnel oxide layer. There is the following defect: due to the influence of the airflow, temperature, electric field, and radio frequency in the tube during the deposition process, the tunnel oxide layer deposited by PECVD has poor uniformity, and the good uniformity technical effect of the present application cannot be achieved. Similarly, if the silicon oxide layer prepared by PEALD is on the inside instead of the outside, the principle of PEALD is to ionize an oxygen source such as nitrous oxide or oxygen to produce oxygen anions, which react with silicon that is introduced into the silicon source and chemically adsorbed on the surface of the substrate to generate silicon oxide. The Si on the surface of the substrate is not consumed, and there is no process of forming a silicon oxide layer from the defective Si. The passivation effect of PECVD on the inside cannot be achieved. In addition, the Si on the surface of the substrate is not consumed, and the effect of PECVD on smoothing the silicon-based surface on the inside cannot be achieved. The quality and uniformity of the generated silicon oxide layer are not as good as those of PECVD on the inside.

[0057] Example 1

[0058] This embodiment provides a method for preparing a TOPCon solar cell, which specifically includes the following steps:

[0059] Step 1: Perform conventional texturing, diffusion, and alkaline polishing treatments on a 182mm×182mm N-type substrate (silicon wafer).

[0060] In the second step, the alkali-polished substrate is subjected to nitrous oxide ionization deposition of the first oxide layer. The nitrous oxide flow rate for depositing the first oxide layer is 10,000 sccm, the power is 8,000 w, the deposition time is 15 s, and the thickness is controlled at 0.1 nm. On the basis of the first oxide layer, a second oxide layer is deposited by plasma-enhanced atomic layer deposition. The total flow rate of argon-carried silicon source is 2,000 sccm, the nitrous oxide flow rate is 2,400 sccm, the deposition time is 90 s, the power is 9,000 w, and the thickness is controlled at 1 nm.

[0061] Step three, plasma enhanced chemical vapor deposition of intrinsic amorphous silicon film, introducing argon and silane mixed gas, RF power of 11000W, deposition temperature of 420℃, process pressure of 300Pa, deposition time of 6min, argon flow rate of 6000sccm, silane flow rate of 2500sccm, and film thickness controlled at 20nm.

[0062] Step 4: Plasma enhanced chemical vapor deposition doped amorphous silicon film, introducing a mixed gas of argon, silane and phosphine, the RF power is 10000W, the deposition temperature is 420℃, the process pressure is 300Pa, the deposition time is 23min, the argon flow rate is 6000sccm, the silane flow rate is 2000sccm, the phosphine flow rate is 3000sccm, and the film thickness is controlled at 130nm.

[0063] Step 5: Plasma-enhanced chemical vapor deposition of a silicon dioxide film, introducing a mixture of silane and nitrous oxide, with a radio frequency power of 10,000 W, a deposition temperature of 420°C, a process pressure of 200 Pa, a deposition time of 1 min, a silane flow rate of 2,500 sccm, a nitrous oxide flow rate of 6,000 sccm, and a film thickness controlled at 12 nm.

[0064] Step six, the substrate after depositing Poly (doped amorphous silicon) is subjected to high temperature annealing to activate the phosphorus atoms in the poly deposition. Then RCA wet chemical cleaning is used to remove the doped amorphous silicon at the edge of the substrate and the phosphorus silicon glass on the surface. Then atomic layer deposition is used to deposit the aluminum oxide film required on the front side (thickness is 1-3nm). Then silicon nitride coating is performed on the front and back sides (front film 70-85nm, back film 80-100nm), and then the electrode printing and sintering (sintering temperature 650-850℃) are carried out in the screen process. Among them:

[0065] RCA wet process: Industry standard wet cleaning process, using hydrofluoric acid to remove the phosphorus silicon glass layer on the surface of the substrate, and using alkali (potassium hydroxide) to remove the doped amorphous silicon layer at the edge of the silicon substrate.

[0066] Atomic layer deposition (ALD) uses chemical reactions between vapor-phase precursor molecules on a surface to deposit thin films layer by layer. During the deposition process, trimethylaluminum and water alternately enter the reaction chamber to form an aluminum oxide film. In this example, the aluminum film thickness is controlled to 2.5nm.

[0067] Front and back films: Plasma chemical vapor deposition is used, ammonia and silane are introduced into the reaction chamber, and silicon nitride is deposited on the front and back of the substrate respectively. The thickness of the front film is controlled to be 80nm and the thickness of the back film is controlled to be 90nm.

[0068] Printing of front and back electrodes: Printing is done based on the basic principle that the slurry is passed through the mesh holes of the graphic part of the screen and the slurry is not passed through the mesh holes of the non-graphic part to prepare the front and back electrodes.

[0069] Sintering: The sintering temperature is 750°C. At high temperature, the silicon atoms in the substrate enter the molten metal electrode material to form an alloy system. After the temperature drops, the silicon atoms in the alloy system will recrystallize to form an epitaxial layer between the silicon wafer and the metal electrode, forming a good ohmic contact.

[0070] Example 2

[0071] This embodiment provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0072] The alkaline-polished substrate was deposited with nitrous oxide (NO) ionization deposition (LIOD) for the first oxide layer. The NO flow rate was 10,000 sccm, the power was 8,000 W, the deposition time was 15 seconds, and the thickness was controlled to 0.1 nm. A second oxide layer was deposited on top of the first oxide layer using plasma-enhanced atomic layer deposition (PEALD) with an argon-carried silicon source flow rate of 2,000 sccm, a NI flow rate of 2,400 sccm, a deposition time of 80 seconds, a power of 9,000 W, and a thickness of 0.9 nm.

[0073] Example 3

[0074] This embodiment provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0075] The alkaline-polished substrate was deposited with nitrous oxide (NO) ionization deposition (LIOD) for the first oxide layer. The NO flow rate was 10,000 sccm, the power was 8,000 W, the deposition time was 15 seconds, and the thickness was controlled to 0.1 nm. A second oxide layer was deposited on top of the first oxide layer using plasma-enhanced atomic layer deposition (PEALD) with an argon-carried silicon source flow rate of 2,000 sccm, a NI flow rate of 2,400 sccm, a deposition time of 70 seconds, a power of 9,000 W, and a thickness of 0.8 nm.

[0076] Example 4

[0077] This embodiment provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0078] The alkaline-polished substrate was deposited with a first oxide layer using plasma chemical vapor deposition (PCVD). The deposition was performed at a nitrous oxide flow rate of 10,000 sccm, a power of 8,000 W, a deposition time of 15 seconds, and a thickness of 0.1 nm. A second oxide layer was deposited on top of the first oxide layer using plasma-enhanced atomic layer deposition (PEALD). The silicon source was carried by argon at a total flow rate of 2,000 sccm, a nitrous oxide flow rate of 2,400 sccm, a deposition time of 100 seconds, a power of 9,000 W, and a thickness of 1.2 nm.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0081] The alkali-polished substrate was subjected to plasma enhanced chemical vapor deposition (PECVD) tunneling oxide layer with a nitrous oxide flow rate of 10,000 sccm, a power of 8,000 W, a deposition time of 120 s, and a thickness controlled at 1 nm.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0084] The alkali-polished substrate was subjected to plasma enhanced chemical vapor deposition (PECVD) tunneling oxide layer with a nitrous oxide flow rate of 10,000 sccm, a power of 8,000 W, a deposition time of 150 s, and a thickness controlled at 1.1 nm.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0087] The tunneling oxide layer was deposited on the alkali-polished substrate. The argon-carrying silicon source flow rate of the complete tunneling oxide layer PEALD was 2000 sccm, the nitrous oxide flow rate was 2400 sccm, the deposition time was 90s, the power was 9000 W, and the thickness was controlled at 0.9 nm.

[0088] Comparative Example 4

[0089] This comparative example provides a method for preparing a TOPCon solar cell. Compared with Example 1, the only difference is that step 2 is different, specifically:

[0090] The alkaline-polished substrate was deposited with a first oxide layer using plasma chemical vapor deposition (PCVD). The deposition was performed at a nitrous oxide flow rate of 10,000 sccm, a power of 8,000 W, a deposition time of 15 seconds, and a controlled thickness of 0.1 nm. A second oxide layer was deposited on top of the first oxide layer using plasma-enhanced atomic layer deposition (PEALD). The silicon source was carried by argon at a total flow rate of 2,000 sccm, a nitrous oxide flow rate of 2,400 sccm, a deposition time of 260 seconds, and a power of 9,000 W, achieving a controlled thickness of 2.9 nm.

[0091] Test Case

[0092] 1. Film uniformity test

[0093] The tunneling oxide layer was prepared according to the methods of each embodiment and comparative example of the present application. During the film thickness test, the deposition time of the second oxide layer of Example 1 / 2 / 3 / 4, the deposition time of the complete tunneling oxide layer of Comparative Example 3, and the deposition time of the second oxide layer of Comparative Example 4 were extended to 280 / 270 / 260 / 290 / 270 / 290s, respectively. The deposition time of the complete tunneling oxide layer of Comparative Example 1 / 2 was extended by 30min (because the overall thickness of the tunneling oxide layer was too low, conventional film thickness test instruments could not measure the thickness, so the actual film thickness was deposited to about 4nm so that its thickness could be measured by an ellipsometer. As the deposition time increased, the thickness of the oxide layer became thicker. If the uniformity of the thick film layer was good, it could also reflect the uniformity of the films grown by different methods). The film thickness test was compared. The differences between the example group and the comparative group were as follows: point 1 is the film thickness at the center of the substrate, and points 2-5 are the film thicknesses at the four corners of the substrate. The substrate was selected at the outer boat page and the middle boat page of the graphite boat. Since a PECVD furnace can typically process many wafers, samples at different locations within the furnace were selected for testing, from A1 to J15. Specific results are shown in Table 1.

[0094] Deposition Time: For the oxide layers deposited via PEALD, i.e., the second oxide layers of Examples 1 / 2 / 3 / 4, the complete oxide layer of Comparative Example 3, and the second oxide layer of Comparative Example 4, there was a linear relationship between the deposition time and thickness of the oxide layers. With increasing deposition time, the thickness increased linearly. For the oxide layers deposited via PECVD, i.e., the oxide layers of Comparative Examples 1 and 2, there was a nonlinear relationship between the deposition time and thickness of the oxide layers. With increasing deposition time, the deposition rate gradually decreased, and it took longer to deposit the same thickness.

[0095] Table 1

[0096] Film thickness uniformity calculation method: The intra-sheet uniformity is calculated using the film thickness value within a single sheet, and the inter-sheet uniformity is calculated using the film thickness values ​​of the group of 12 sheets. The smaller the uniformity value, the better the film thickness uniformity.

[0097] As can be seen from the data in Table 1, the inter-sheet uniformity of Examples 1 / 2 / 3 / 4 is significantly better than that of Comparative Examples 1 / 2, indicating that the uniformity of the oxide layer formed by PECVD+PEALD is significantly better than that of the oxide layer formed entirely by PECVD in the prior art.

[0098] In addition, as mentioned above, when the overall thickness of the tunneling oxide layer is low, conventional film thickness testing instruments (such as ellipsometers) cannot measure the thickness. The data of observing the cross section of the tunneling oxide layer and calculating the uniformity using a scanning electron microscope (SEM) are now supplemented. Among them, the tunneling oxide layer is prepared by referring to the method of the embodiment of the present application, the first oxide layer is prepared by PECVD, and the second oxide layer is prepared by PEALD. The overall thickness is controlled to be 1.4nm (wherein, the thickness of the first oxide layer is controlled to be 0.4nm, and the thickness of the second oxide layer is controlled to be 1nm). The control experiment uses PECVD to prepare the tunneling oxide layer, and the thickness is controlled to be 1.4nm. The uniformity data within the SEM test piece are shown in the following Table 2 and Figure 1, where point 1 corresponds to the film thickness at the center of the substrate, and the remaining points correspond to the four sides and four corners of the substrate. It can also be seen from Table 2 that the uniformity of the oxide layer formed by PECVD+PEALD is significantly better than the oxide layer formed entirely by PECVD in the prior art.

[0099] Table 2

[0100] 2. Electrical performance test

[0101] The TOPCon solar cells obtained in the above embodiments and comparative examples were subjected to electrical performance tests. The specific test steps and parameters are as follows. The electrical performance parameters reflecting the passivation effect of the cell are open circuit voltage and photoelectric conversion efficiency.

[0102] Open circuit voltage: Use a voltmeter or photoelectric conversion efficiency tester to measure the open circuit voltage of a solar cell when it is not connected to a load. At this time, the output current of the solar cell is zero.

[0103] Short-circuit current: Use an ammeter or photoelectric conversion efficiency tester to measure the short-circuit current of a solar cell when the substrate is short-circuited. At this time, the output voltage of the solar cell is zero.

[0104] Conversion efficiency: Use a photoelectric conversion efficiency tester to measure the output power and absorbed light power of the solar cell under standard lighting conditions to calculate the conversion efficiency of the solar cell.

[0105] Fill factor: Use a photoelectric conversion efficiency tester to measure the output current and output voltage of the solar cell under standard lighting conditions to calculate the fill factor of the solar cell.

[0106] Series resistance: Use a resistance meter to measure the series resistance of a solar cell. Series resistance affects the output voltage and conversion efficiency of the solar cell.

[0107] Parallel resistance: Use a resistance meter to measure the parallel resistance of a solar cell. Parallel resistance affects the output current and conversion efficiency of the solar cell.

[0108] Leakage current: Use an ammeter or photoelectric conversion efficiency tester to measure the leakage current of the solar cell when the solar cell load is not connected.

[0109] Table 3

[0110] Table 4

[0111] It can be seen from the data in Table 3-4 that the sum of the thickness of the first oxide layer and the second oxide layer of Example 1 is the same as the thickness of the oxide layer of Comparative Example 2, the sum of the thickness of the first oxide layer and the second oxide layer of Example 2 is the same as the thickness of the oxide layer of Comparative Example 1, and the sum of the thickness of the first oxide layer and the second oxide layer of Example 3 is the same as the thickness of the oxide layer of Comparative Example 3. The total thickness of the tunneling oxide layer formed in these three groups is the same, but the formation method is different. The open circuit voltage and photoelectric conversion efficiency parameters of Examples 1-3 are better than those of Comparative Examples 1-3, and the examples can achieve good technical effects. In the field of industrialized solar cells, the improvement of the photoelectric conversion efficiency of the battery can significantly improve the power of the photovoltaic module packaged by multiple cells, and the above-mentioned improvement is a significant improvement. This proves that compared with the oxide layer obtained by using PECVD alone or PEALD alone, even if the thickness of the tunneling oxide layer obtained is the same, the combination of PECVD and PEALD in this application has achieved unexpected technical effects.

[0112] In addition, as shown in the above comparative example 4, even if PECVD and PEALD are used in combination, if the thickness range is not within the range of "the thickness of the first oxide layer is 0.1-0.5 nm" and "the thickness of the second oxide layer is 0.3-2 nm" defined in this application, the electrical properties that can be obtained in Examples 1-4 of the present application cannot be achieved.

[0113] It can be seen from the above data that the technical solution of the embodiment of the present application increases the chemical passivation of the substrate surface, reduces the damage to the substrate surface caused by plasma bombardment, and improves the uniformity of the tunneling oxide layer (Table 1, Table 2); at the same time, it improves the photoelectric conversion efficiency of the TOPCon cell without adding equipment (Table 3).

[0114] The preparation method of the TOPCon solar cell provided by the present invention changes the method of preparing the tunnel oxide layer entirely by PECVD, and switches to a method of combining PECVD and PEALD to deposit the tunnel oxide layer. This application is based on the difference in the principles of PECVD and PEALD deposition processes, so that the two are combined to play a role of mutual correlation and mutual promotion. PECVD deposition provides a high-quality c-Si / SiOx interface, and PEALD is deposited on the high-quality interface, which solves the technical problem of precise control of the atomic-level thickness required for tunneling in the tunnel oxide layer, as well as the uniformity and passivation effect required for the thin film, and avoiding damage to the substrate surface. Specifically, in the specific implementation method of the present application, by the PECVD method, first, a surface Si-based oxidation scheme is adopted to grow a first oxide layer of 0.1-0.5nm, and the silicon-based surface is flattened and cleaned, and internal defects are compositely passivated. Next, the PEALD method is adopted to grow a second oxide layer of 0.3-2nm atomic layer epitaxial growth, which can achieve precise control of the thickness of the tunnel oxide layer at the atomic level. The second oxide layer formed on the basis of the first oxide layer on the flattened silicon-based surface has good uniformity. Judging from the final process results, the composite oxide layer has significantly better uniformity and good chemical passivation of the interface contact, which is directly reflected in the electrical performance of the solar cell, namely the improvement in open circuit voltage and photoelectric conversion efficiency brought about by the improved passivation (see the data in Table 3 of this application), and the normal distribution of the conversion efficiency of the batch of solar cells is more convergent.

[0115] That is, the present application utilizes a combination of PECVD and PEALD, which are interrelated and mutually reinforcing. On the basis of a high-quality interface oxide layer, it realizes the application requirement of precise control of the thickness of the tunneling oxide layer at the atomic level, improves the problem of poor tunneling uniformity caused by the long tunneling oxide layer produced by PECVD, and also retains the passivation effect of the underlying oxide layer on the surface, which can avoid electroluminescence test (EL) failures such as card point marks caused by the tunneling oxide layer produced entirely by nitrous oxide ionization, and reduce the damage of the plasma bombardment on the substrate surface, thereby improving the conversion efficiency (passivation effect) of the TOPCon solar cell to a certain extent.

[0116] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a TOPCon solar cell, characterized in that: It includes a tunneling oxide layer, and the preparation method of the tunneling oxide layer includes the following steps: depositing a first oxide layer on the surface of a substrate by plasma enhanced chemical vapor deposition, and depositing a second oxide layer by plasma enhanced atomic deposition, wherein the thickness of the first oxide layer is 0.1-0.5nm.

2. The method for preparing a TOPCon solar cell according to claim 1, characterized in that: The thickness of the first oxide layer is 0.1-0.2 nm.

3. The method for preparing a TOPCon solar cell according to claim 1, characterized in that: The thickness of the second oxide layer is 0.3-2 nm.

4. The method for preparing a TOPCon solar cell according to any one of claims 1 to 3, characterized in that: The steps include: S1, texturing, diffusion and alkali polishing of the substrate; S2, depositing a tunnel oxide layer; S3, depositing an intrinsic amorphous silicon layer; S4, depositing a doped amorphous silicon layer; S5, depositing a silicon dioxide layer; S6, annealing, wet process, atomic layer deposition, coating, front and back electrode printing, sintering.

5. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: In step S3, an intrinsic amorphous silicon layer is deposited by plasma enhanced chemical vapor deposition technology; And / or, the thickness of the intrinsic amorphous silicon layer is 10-20 nm.

6. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: In step S4, a doped amorphous silicon layer is deposited using plasma enhanced chemical vapor deposition technology; And / or, the thickness of the doped amorphous silicon layer is 20-130 nm; And / or, the doped amorphous silicon layer is composed of a phosphorus-doped amorphous silicon layer.

7. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: In step S5, a silicon dioxide layer is deposited by plasma enhanced chemical vapor deposition technology; And / or, the thickness of the silicon dioxide layer is 10-15 nm.

8. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: In step S1, the operation of the texturing step is to form a velvet shape on the surface of the substrate by using alkali etching; And / or, the diffusion step is performed by doping boron element on the front surface of the substrate; And / or, the alkali polishing step is performed to form a polished surface on the back side of the substrate.

9. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: In step S6, the operation of the wet process is to remove the doped amorphous silicon layer at the edge of the substrate and the phosphosilicate glass layer on the back surface of the substrate; And / or, the atomic layer deposition step is performed by depositing an aluminum oxide passivation layer on the front surface of the substrate; And / or, the coating step is performed by coating a silicon nitride anti-reflection layer on the front and back sides of the substrate; And / or, the sintering temperature is 750-800° C. and the sintering time is 1-2 min.

10. A TOPCon solar cell prepared according to the preparation method according to any one of claims 1 to 9.

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