A solar cell and a method of manufacturing the same

Abstract

The present disclosure provides a solar cell and a preparation method thereof, and belongs to the technical field of solar cells. The back surface of the solar cell has a passivation contact structure only at the position corresponding to the non-metallic region. The passivation contact structure forms an etching step with an inclination angle of 40-60 degrees at the position where the metallic region and the non-metallic region meet. The etching step with the above inclination angle can make the transition between the non-metallic region and the metallic region smoother than the vertical etching step, and is more conducive to the uniformity of the subsequent passivation film layer and the transportation of back surface carriers, thereby improving the passivation level of the solar cell. The preparation of the solar cell comprises: double-sided texturing, boron diffusion and oxidation, BSG removal and alkali etching, LPCVD and phosphorus diffusion, and back surface patterning of the N-type silicon substrate; removing the PSG on the front surface of the N-type silicon substrate, using an alkali solution and a specific anti-plating additive for RCA cleaning, and removing the tunneling oxide layer and the doped polysilicon layer on the back surface of the N-type silicon substrate corresponding to the metallic region.

Description

Technical Field

[0001] This disclosure relates to the field of solar cell technology, and more specifically, to a solar cell and a method for its fabrication. Background Technology

[0002] In recent years, N-TOPCon cell technology has become the mainstream cell technology in the photovoltaic industry, and its cell technology has developed rapidly, with high efficiency and low cost as its main features. The core structure of TOPCon cells is to prepare an ultra-thin silicon oxide layer on the back of the cell, and then deposit a layer of doped polycrystalline silicon. The two together form a passivation contact structure, which can effectively reduce surface recombination and metal contact recombination. Although the thin layer of doped polycrystalline silicon on the back optimizes the passivation of the back metal region, the grain boundaries of the doped polycrystalline silicon are prone to photorecombination, which also affects the light absorption effect.

[0003] To address the aforementioned issues, the N-type polyfinger process of TOPCon cells removes the tunneling oxide layer and doped polysilicon layer in the non-metallic region, retaining only the tunneling oxide layer and polysilicon layer structure on the substrate below the metal region. This reduces parasitic light absorption by the back-side tunneling oxide and doped polysilicon layer without affecting the passivation improvement of the metal region, thus resulting in better cell conversion efficiency. However, current methods typically use laser-superimposed wet chemical processes to remove the tunneling oxide and doped polysilicon in the non-metallic region. After removing the tunneling oxide and doped polysilicon, this process creates a vertical step-like corrosion morphology at the junction of the metal and non-metallic regions. This step-like corrosion morphology connects the metal and non-metallic regions on the left and right sides, respectively, with a height difference of 3±2μm between them. This height difference inevitably affects the deposition of the passivation film on the back of the cell and the transport of charge carriers.

[0004] In view of this, this disclosure is hereby made. Summary of the Invention

[0005] The purpose of this disclosure is to provide a solar cell and a method for its fabrication, in order to solve or improve the aforementioned technical problems.

[0006] This disclosure can be implemented as follows: In a first aspect, this disclosure provides a solar cell, wherein the back side of the solar cell has a passivation contact structure only corresponding to the non-metallic region, and the passivation contact structure forms a corrosion step at the junction of the metallic and non-metallic regions, wherein the sidewall of the corrosion step has an inclination angle of 40° to 60°.

[0007] In an optional embodiment, the sidewalls of the corrosion step have an inclination angle of 42.6° to 56.8°.

[0008] In an optional embodiment, the solar cell includes an N-type silicon substrate, the front side of which comprises P-type silicon substrates from the inside out.+ The N-type silicon substrate has an emitter, a front passivation layer, a front anti-reflection film, and a metal electrode. The back side of the N-type silicon substrate has a passivation contact structure at the corresponding non-metallic region. The passivation contact structure includes, from the inside out, a tunneling oxide layer, a doped polysilicon layer, a back passivation layer, and a back anti-reflection film. The back side of the N-type silicon substrate has a metal electrode at the corresponding metallic region.

[0009] In a second aspect, this disclosure provides a method for fabricating a solar cell as described in the foregoing embodiments, comprising the following steps: texturing an N-type silicon substrate on both sides, boron expansion and oxidation, removing BSG and alkaline polishing, LPCVD and phosphorus expansion, and back-side patterning; removing the PSG on the front side of the N-type silicon substrate, and removing the tunneling oxide layer and the doped polycrystalline silicon layer of the corresponding metal region on the back side of the N-type silicon substrate by RCA cleaning. The cleaning solution used for RCA cleaning includes alkali, plating remover additives, and water. The plating remover additives include aromatic carboxylic acid complexing agents, surfactants, wetting agents, organic acid salt pH buffers, and water. The concentration of the plating remover additives in the cleaning solution is 0.15wt%~0.25wt%.

[0010] In an optional embodiment, the concentration of the plating remover additive in the cleaning solution is 0.18wt% to 0.22wt%.

[0011] In an optional embodiment, the concentration of alkali in the cleaning solution is 0.1wt% to 0.3wt%.

[0012] In an optional embodiment, the de-coating additive contains, by mass percentage, 1 wt% to 2 wt% sodium benzoate, 1 wt% to 3 wt% surfactant, 5 wt% to 7 wt% wetting agent, ≤2 wt% sodium citrate, and the balance being water.

[0013] In an optional embodiment, the aromatic carboxylate complexing agent includes at least one of sodium benzoate, ammonium benzoate, phthalate and salicylate; And / or, the surfactant includes at least one of dodecyl dimethyl betaine, fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sulfate and alkylbenzene sulfonate; And / or, the wetting agent includes at least one of polyether-modified siloxane, alkyl-modified polysiloxane, and gemynyl alcohol; And / or, organic acid salt pH buffers include at least one of sodium citrate, potassium citrate, sodium EDTA, and hydroxyethylidene diphosphonic acid.

[0014] In an optional implementation, the RCA cleaning time is 300s~400s and the temperature is 55℃~75℃.

[0015] In an optional implementation, after RCA cleaning, double-sided ALD, double-sided coating, and screen printing are also performed.

[0016] The beneficial effects of this disclosure include: The solar cell disclosed herein features a passivation contact structure with corrosion steps at an angle of 40° to 60° at the junction of the metal and non-metal regions. Compared to vertical corrosion steps, this results in a smoother transition between the non-metal and metal regions, which is more conducive to the uniformity of the subsequent passivation film and the transport of charge carriers on the back side, thereby improving the passivation level and photoelectric performance of the solar cell. The aforementioned angled corrosion steps can be achieved by using a specific concentration and composition of de-coating additives during the RCA cleaning process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the fabrication process of the solar cell provided in this disclosure; Figure 2 This is a schematic diagram showing the inclination angle of the corrosion step in the solar cell prepared in Example 1 of this disclosure; Figure 3 This is a schematic diagram showing the tilt angle of the corrosion step in the solar cell prepared in Comparative Example 1 of this disclosure. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The solar cells and their fabrication methods disclosed herein are described in detail below.

[0021] This disclosure provides a solar cell with a passivation contact structure on the back side corresponding only to the non-metallic region. The passivation contact structure forms a corrosion step at the junction of the metallic and non-metallic regions, and the sidewall of the corrosion step has an inclination angle of 40° to 60°.

[0022] In this disclosure, the angle of the sidewall inclination of the etching step refers to the angle between the sidewall of the etching step and the direction parallel to the surface of the silicon substrate.

[0023] In some alternative embodiments, the inclination angle of the corrosion step sidewall can be 40°, 45°, 50°, 55°, or 60°, or other values ​​within the range of 40° to 60°. In some preferred embodiments, the inclination angle of the corrosion step sidewall is 42.6° to 56.8°.

[0024] The aforementioned angled corrosion steps, compared to the vertical corrosion steps in existing technologies, provide a smoother transition between non-metallic and metallic regions, which is more conducive to the uniformity of the subsequent passivation film and the transport of charge carriers on the back side, thereby improving the passivation level of the solar cell. However, if the angle of the corrosion step sidewall is less than 40°, it indicates that the corrosion depth is too shallow and the RCA cleaning effect is poor; if the angle of the corrosion step sidewall is greater than 60°, it is easy to cause uneven deposition of the subsequent passivation film.

[0025] In some alternative embodiments, the solar cell includes an N-type silicon substrate, the front side of which comprises, from the inside to the outside, P... + The N-type silicon substrate has an emitter, a front passivation layer, a front anti-reflection film, and a metal electrode. The back side of the N-type silicon substrate has a passivation contact structure at the corresponding non-metallic region. The passivation contact structure includes, from the inside out, a tunneling oxide layer, a doped polysilicon layer, a back passivation layer, and a back anti-reflection film. The back side of the N-type silicon substrate has a metal electrode at the corresponding metallic region.

[0026] Among them, N-type silicon substrates, as the base material for batteries, have advantages such as long minority carrier lifetime and no boron-oxygen recombination centers, which can achieve lower light-induced degradation.

[0027] The passivation contact structure on the back side consists of two ultrathin films. A tunneling oxide layer covers the surface of the N-type silicon substrate, allowing majority carriers (electrons) to efficiently tunnel through via quantum tunneling while preventing minority carriers (holes) from recombinating on the surface, significantly reducing recombination current. A doped polycrystalline silicon layer is deposited on top of the tunneling oxide layer, forming a passivation contact together with the tunneling oxide layer. This provides a lateral transport channel for electrons, which are ultimately collected by the back metal electrode.

[0028] P + The emitter is formed on the front side of the N-type silicon substrate through boron diffusion, forming a pn junction with the N-type silicon substrate.

[0029] The front passivation layer is used to passivate the silicon wafer surface and reduce carrier recombination; it can be an aluminum oxide layer.

[0030] The front anti-reflective coating is used to reduce light reflection loss and protect the underlying aluminum oxide layer, which can be a silicon nitride layer.

[0031] Metal electrodes are used to collect current; they can be metal grids such as silver or copper.

[0032] Continuing on the above, the solar cell provided in this disclosure improves the deposition of subsequent passivation film and reduces the formation of recombination centers by optimizing the surface contact between the non-metallic and metallic regions, thereby effectively improving the electrical performance of the solar cell, such as increasing the photoelectric conversion efficiency, open-circuit voltage, short-circuit current and fill factor.

[0033] Accordingly, this disclosure also provides a method for preparing the above-mentioned solar cell, such as... Figure 1 As shown, the process includes the following steps: double-sided texturing, boron diffusion and oxidation, BSG removal and alkaline polishing, LPCVD and phosphorus diffusion, and back-side patterning of the N-type silicon substrate; removal of PSG on the front side of the N-type silicon substrate; and removal of the tunnel oxide layer and doped polysilicon layer of the corresponding metal region on the back side of the N-type silicon substrate by RCA cleaning.

[0034] Double-sided flocking The N-type silicon substrate is textured on both sides to remove metallic impurities and organic dirt from its surface.

[0035] In some alternative implementations, the texturing time can be 420s to 460s (e.g., 420s, 430s, 440s, 450s or 460s, etc.), and the temperature can be 70℃ to 90℃ (e.g., 70℃, 75℃, 80℃, 85℃ or 90℃, etc.).

[0036] In some optional embodiments, the texturing solution used for texturing includes an alkali, a texturing additive, and water. The concentration of the alkali in the texturing solution can be 0.2 wt% to 0.8 wt%, such as 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, or 0.8 wt%. The concentration of the texturing additive in the texturing solution can be 0.02 wt% to 0.18 wt%, such as 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, or 0.18 wt%. The alkali may, by example, include at least one of sodium hydroxide and potassium hydroxide. The texturing additive includes nucleating agents, surfactants, catalysts, dispersants, and defoamers, and may specifically employ conventional texturing additives in the art.

[0037] Boron dilution and oxidation P-type silicon substrates are formed on the front side of an N-type silicon substrate by boron diffusion. + Emitter. A BSG layer is formed on the front side and the edge of the back side of the N-type silicon substrate through an oxidation process.

[0038] In some optional embodiments, the boron diffusion temperature can be 430℃~480℃ (e.g., 430℃, 450℃, or 480℃), the boron diffusion time can be 420s~480s (e.g., 420s, 450s, or 480s), the boron source flow rate can be 220sccm~260sccm (e.g., 220sccm, 240sccm, or 260sccm), the oxygen flow rate can be 600sccm~640sccm (e.g., 600sccm, 620sccm, or 640sccm), and the nitrogen flow rate can be 1980sccm~2020sccm (e.g., 1980sccm, 2000sccm, or 2020sccm).

[0039] After boron expansion, it first undergoes propulsion and then high-temperature oxidation.

[0040] In some alternative implementations, the propulsion temperature can be 980°C to 1020°C (e.g., 980°C, 1000°C, or 1020°C), and the propulsion time can be 1130s to 1170s (e.g., 1130s, 1150s, or 1170s).

[0041] In some alternative embodiments, the oxidation temperature can be 1030℃~1070℃ (e.g., 1030℃, 1050℃ or 1070℃), and the oxidation time can be 3730s~3770s (e.g., 3730s, 3750s or 3770s).

[0042] The boron source may, by way of example, include at least one of boron trichloride (BCl3), borane (B2H6) and trimethyl borate (B(OCH3)3), with boron trichloride being preferred.

[0043] Remove BSG and alkaline polishing The boron-expanded and oxidized silicon substrate undergoes a backside BSG removal process. The backside of the BSG-removed N-type silicon substrate is then subjected to alkaline polishing to remove the naturally formed oxide layer on the backside of the N-type silicon substrate.

[0044] In some alternative implementations, BSG removal can be performed by chain cleaning for 60s to 100s (e.g., 60s, 80s, or 100s) with an aqueous HF solution of 7wt% to 13wt% (e.g., 7wt%, 10wt%, or 13wt%).

[0045] In some optional embodiments, the alkaline polishing time can be 150s~250s (e.g., 150s, 180s, 200s, 220s or 250s, etc.), and the alkaline polishing temperature can be 50℃~70℃ (e.g., 50℃, 55℃, 60℃, 65℃ or 70℃, etc.).

[0046] In some optional embodiments, the alkaline polishing solution used includes an alkali, an alkaline polishing additive, and water. The concentration of the alkali in the alkaline polishing solution can be 0.1 wt% to 0.3 wt%, such as 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, or 0.3 wt%. The concentration of the alkaline polishing additive in the alkaline polishing solution can be 0.02 wt% to 0.18 wt%, such as 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, or 0.18 wt%. The alkali can exemplary include at least one of sodium hydroxide and potassium hydroxide. The alkaline polishing additive can exemplary include surfactants, chelating agents, organic acids, catalysts, and dispersants, specifically using conventional alkaline polishing additives in the art.

[0047] LPCVD and phosphorus diffusion A tunneling oxide layer and a doped polycrystalline silicon layer are deposited on the silicon substrate after BSG removal and alkaline polishing. An intrinsic amorphous silicon layer is first prepared on the surface of the tunneling oxide layer, and then the intrinsic amorphous silicon layer is subjected to phosphorus doping treatment to convert the amorphous silicon into polycrystalline silicon, thus forming a doped polycrystalline silicon layer.

[0048] In some optional embodiments, the preparation conditions of the tunneling oxide layer include: the deposition temperature can be 550℃~650℃ (e.g., 550℃, 600℃ or 650℃), the oxygenation time can be 250s~350s (e.g., 250s, 300s or 350s), and the oxygenation time can be 350s~750s (e.g., 350s, 550s or 750s).

[0049] The preparation conditions for the intrinsic amorphous silicon layer include: the temperature can be 550℃~650℃ (such as 550℃, 600℃ or 650℃, etc.), and the reaction time can be 1600s~2000s (such as 1600s, 1800s or 2000s, etc.).

[0050] The conditions for phosphorus doping treatment include: deposition temperature of 590℃~990℃ (e.g., 590℃, 690℃, or 990℃), time of 600s~1000s (e.g., 600s, 800s, or 1000s), phosphorus source flow rate of 1200sccm~1600sccm (e.g., 1200sccm, 1400sccm, or 1600sccm), and oxygen flow rate of 30sccm~70sccm (e.g., 30sccm, 50sccm, or 70sccm).

[0051] The conditions for converting amorphous silicon into polycrystalline silicon include: a driving temperature of 780℃~880℃ (e.g., 780℃, 830℃, or 880℃), and a time of 860s~1060s (e.g., 860s, 960s, or 1060s). An oxidation temperature of 800℃~900℃ and a time of 800s~1000s (e.g., 800s, 900s, or 1000s).

[0052] The phosphorus source may, by way of example, include at least one of phosphorus oxychloride (POCl3), phosphine (PH3), and phosphorus pentoxide (P2O5), preferably phosphorus oxychloride.

[0053] Backside Graphics In some alternative implementations, a green skin laser can be used to laser pattern the PSG on the back non-metallic region of the phosphorus-expanded silicon substrate, thereby vaporizing or loosening it.

[0054] For example, a large rectangular spot with a size of (100μm~200μm)×(100μm~200μm) can be used, with 10%~90% overlap in both the X and Y axes.

[0055] Go to PSG and RCA After the back side is patterned, the front side is first de-PSG, and then the tunneling oxide layer and doped polysilicon layer on the front side are removed by RCA. At the same time, the tunneling oxide layer and doped polysilicon layer in the non-metallic area on the back side are removed, thereby improving the surface contact and passivation effect of the non-metallic area.

[0056] In some alternative implementations, removing PSG from the front side of the N-type silicon substrate may include: performing a chain cleaning for 60s to 100s (e.g., 60s, 80s, or 100s) with an aqueous HF solution of a concentration of 9wt% to 15wt% (e.g., 9wt%, 12wt%, or 15wt%).

[0057] In some alternative implementations, the cleaning solution used for RCA cleaning includes alkali, plating remover additives, and water.

[0058] The concentration of alkali in the cleaning solution can be 0.1wt%~0.3wt% (e.g., 0.1wt%, 0.2wt%, or 0.3wt%), and the concentration of plating remover in the cleaning solution can be 0.15wt%~0.25wt% (e.g., 0.15wt%, 0.2wt%, or 0.25wt%).

[0059] In this disclosure, the concentration of the de-coating additive in the cleaning solution directly affects the inclination angle of the corrosion step sidewall. If the concentration of the de-coating additive in the cleaning solution is less than 0.15 wt%, the inclination angle of the corrosion step sidewall will be less than 40°, approaching parallelism; if the concentration of the de-coating additive in the cleaning solution is greater than 0.25 wt%, the inclination angle of the corrosion step sidewall will be greater than 60°, resulting in excessive tilting.

[0060] In some preferred embodiments, the concentration of the de-plating additive in the cleaning solution is 0.18wt% to 0.22wt%, and the sidewall inclination angle of the corrosion step formed at this concentration range is optimal.

[0061] In some alternative implementations, the de-coating additives include aromatic carboxylate complexing agents, surfactants, wetting agents, organic acid salt pH buffers, and water.

[0062] Among them, aromatic carboxylate complexing agents mainly play a role in complexation and stabilization, surfactants mainly play a role in reducing surface tension, promoting penetration and emulsification, wetting agents mainly play a role in enhancing wetting and spreading and preventing droplet aggregation, and organic acid salt pH buffers mainly play a role in complexing metal ions and buffering pH value.

[0063] Aromatic carboxylate complexing agents may, exemplarily, include at least one of sodium benzoate, ammonium benzoate, phthalate, and salicylate. Surfactants may, exemplarily, include at least one of dodecyl dimethyl betaine, fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sulfate, and alkylbenzene sulfonate. Wetting agents may, exemplarily, include at least one of polyether-modified siloxane, alkyl-modified polysiloxane, and gemynyl alcohol. Organic acid salt pH buffers may, exemplarily, include at least one of sodium citrate, potassium citrate, sodium ethylenediaminetetraacetate, and hydroxyethylidene diphosphonic acid.

[0064] In some alternative embodiments, the de-coating additive may contain, by weight percentage, 1 wt% to 2 wt% (e.g., 1 wt%, 1.5 wt%, or 2 wt%) of aromatic carboxylate complexing agent, 1 wt% to 3 wt% (e.g., 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3 wt%) of surfactant, 5 wt% to 7 wt% (e.g., 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, or 7 wt%) of wetting agent, ≤2 wt% of organic acid salt pH buffer (e.g., 0.5 wt%, 1 wt%, 1.5 wt%, or 2 wt%), with the balance being water.

[0065] If the content of aromatic carboxylate complexing agent is less than 1 wt%, it is not conducive to sufficient complexation of reaction products, resulting in incomplete removal of the coating. If the content of aromatic carboxylate complexing agent is more than 2 wt%, it is not conducive to cost control and may corrode the substrate due to excessive complexation. If the content of surfactant is less than 1 wt%, it is not conducive to uniform spread of the solution on the silicon wafer surface, resulting in uneven removal effect. If the content of surfactant is more than 3 wt%, it is easy to generate too much foam, affecting process stability and increasing cleaning difficulty. If the content of wetting agent is less than 5 wt%, it is not conducive to sufficient contact between the solution and the silicon wafer surface, resulting in coating residue. If the content of wetting agent is more than 7 wt%, it is easy to increase the viscosity of the solution, affecting the reaction rate and causing raw material waste. If the content of organic acid salt pH buffer is more than 2 wt%, it is easy to cause excessive fluctuation of the pH value of the solution system, affecting the overall stability of the additive.

[0066] In some alternative implementations, the RCA cleaning time can be 300s to 400s (e.g., 300s, 350s, or 400s), and the temperature can be 55℃ to 75℃ (e.g., 55℃, 60℃, 65℃, 70℃, or 75℃).

[0067] If the RCA cleaning time is too short or the temperature is too low, it will not be conducive to the removal of doped polysilicon; if the RCA cleaning time is too long or the temperature is too high, it will not be conducive to maintaining the protective effect of the non-laser area, resulting in over-corrosion.

[0068] Furthermore, after RCA cleaning, double-sided ALD, double-sided coating, and screen printing may also be performed.

[0069] Double-sided ALD After RCA cleaning, aluminum oxide is deposited on both sides of the silicon substrate to form a passivation layer with a thickness of 2nm~6nm.

[0070] Double-sided coating The silicon substrate after double-sided ALD treatment undergoes double-sided coating. Specifically, a silicon nitride composite layer is deposited on the front side to form an anti-reflection and passivation film. A silicon nitride composite layer is also deposited on the back side to form an anti-reflection and passivation film. Because the transition region between the metal and non-metal regions is flatter, a denser and smoother alumina-silicon nitride thin film is formed in the transition region, which helps reduce the recombination rate of charge carriers and improves the electrical performance, reliability, and stability of the battery.

[0071] screen printing The double-sided coated silicon substrate is screen-printed. The positive electrode structure is formed using silver-aluminum paste on the front side, and the negative electrode structure is formed using silver paste on the back side. Then, laser-assisted sintering technology is used to achieve a reliable connection between the electrode and the battery substrate.

[0072] It should be noted that any content not further elaborated in this disclosure can be found in the relevant prior art, which is conventional and well-known in the field, and will not be elaborated or limited here.

[0073] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0074] Example 1 This embodiment provides a solar cell, which includes an N-type silicon substrate. The front side of the N-type silicon substrate includes, from the inside to the outside, P... + The substrate comprises an emitter, a front passivation layer, a front antireflective coating, and a metal electrode. The back side of the N-type silicon substrate has a passivation contact structure at the corresponding non-metallic region. This passivation contact structure, from the inside out, includes a tunneling oxide layer and a doped polysilicon layer. The back side of the N-type silicon substrate has a metal electrode at the corresponding metallic region. The passivation contact structure forms an etching step at the junction of the metallic and non-metallic regions, with the sidewalls of the etching step having a 53.1° inclination angle.

[0075] The method for fabricating this solar cell includes the following steps: S1: Double-sided texturing of the N-type silicon substrate.

[0076] The N-type silicon substrate was texturized on both sides to remove metallic impurities and organic contaminants from its surface. The texturing time was 440 seconds at 80°C. The texturing solution used included alkali, texturing additives, and water. The concentration of alkali (NaOH) in the texturing solution was 0.5 wt%, and the concentration of the texturing additives was 0.1 wt%.

[0077] S2: Boron diffusion and oxidation.

[0078] P-type silicon substrates are formed on the front side of an N-type silicon substrate by boron diffusion. + Emitter. A BSG layer is formed on the front side and the edge of the back side of the N-type silicon substrate through an oxidation process.

[0079] The boron diffusion temperature was 450℃, the diffusion time was 450s, the boron source flow rate was 240sccm, the oxygen flow rate was 620sccm, and the nitrogen flow rate was 2000sccm. After boron diffusion, the gas underwent a propulsion process followed by high-temperature oxidation. The propulsion temperature was 1000℃, and the propulsion time was 1150s. The oxidation temperature was 1050℃, and the oxidation time was 3750s. The boron source was BCl3.

[0080] S3: Remove BSG and alkali polishing.

[0081] The boron-expanded and oxidized silicon substrate undergoes a backside BSG removal process. The backside of the BSG-removed N-type silicon substrate is then subjected to alkaline polishing to remove the naturally formed oxide layer on the backside of the N-type silicon substrate.

[0082] BSG removal involved a chain cleaning process of 80 seconds using a 10wt% HF aqueous solution. Alkaline polishing was performed for 200 seconds at a temperature of 60°C. The alkaline polishing solution consisted of alkali, an alkaline polishing additive, and water. Specifically, the concentration of alkali (NaOH) in the alkaline polishing solution was 0.2wt%, and the concentration of the alkaline polishing additive was 0.1wt%.

[0083] S4: LPCVD and phosphorus diffusion.

[0084] A tunneling oxide layer and a doped polycrystalline silicon layer are deposited on the silicon substrate after BSG removal and alkaline polishing. An intrinsic amorphous silicon layer is first prepared on the surface of the tunneling oxide layer, and then the intrinsic amorphous silicon layer is subjected to phosphorus doping treatment to convert the amorphous silicon into polycrystalline silicon, thus forming a doped polycrystalline silicon layer.

[0085] The preparation conditions for the tunneling oxide layer include: deposition temperature of 600℃, oxygen purging time of 300s, and oxygen curing time of 550s. The preparation conditions for the intrinsic amorphous silicon layer include: temperature of 600℃ and reaction time of 1800s. The phosphorus doping treatment conditions include: deposition temperature of 790℃, time of 800s, phosphorus source flow rate of 1400 sccm, and oxygen flow rate of 50 sccm. The phosphorus source is POCl3.

[0086] The conditions for converting amorphous silicon into polycrystalline silicon include: a driving temperature of 830°C and a time of 960 s; and an oxidation temperature of 880°C and a time of 900 s.

[0087] S5: Backside graphic design.

[0088] A green laser was used to pattern the PSG (phosphorus-dilated phosphorus photopolymer) in the non-metallic region on the back side of the phosphorus-dilated silicon substrate, thereby vaporizing or loosening it. A large rectangular spot with dimensions of 150 μm × 150 μm was used, with 50% overlap in both the X and Y axes.

[0089] S6: Go to PSG and RCA After the back side is patterned, the front side is first de-PSG, and then the tunneling oxide layer and doped polysilicon layer on the front side are removed by RCA. At the same time, the tunneling oxide layer and doped polysilicon layer in the non-metallic area on the back side are removed.

[0090] Removing PSG from the front side of an N-type silicon substrate may include: chain cleaning for 80 seconds using a 12wt% HF aqueous solution.

[0091] The cleaning solution used for RCA cleaning includes alkali, plating remover, and water. The concentration of alkali in the cleaning solution is 0.2 wt%, and the concentration of plating remover is 0.2 wt%. By mass percentage, the plating remover contains 1.5 wt% sodium benzoate, 2 wt% surfactant (dodecyl dimethyl betaine), 6 wt% wetting agent (polyether-modified siloxane), 1 wt% sodium citrate, and the balance is water. The RCA cleaning time is 350 seconds, and the temperature is 65°C.

[0092] S7: Double-sided ALD.

[0093] After RCA cleaning, aluminum oxide was deposited on both sides of the silicon substrate to form a passivation layer with a thickness of 4 nm.

[0094] S8: Double-sided coating.

[0095] The silicon substrate after double-sided ALD treatment is subjected to double-sided coating treatment. Specifically, silicon nitride composite layers are deposited on the front and back sides to form anti-reflection and passivation films.

[0096] S9: Screen printing.

[0097] The double-sided coated silicon substrate is screen-printed. The positive electrode structure is formed using silver-aluminum paste on the front side, and the negative electrode structure is formed using silver paste on the back side. Then, laser-assisted sintering technology is used to connect the electrodes to the battery substrate.

[0098] Example 2 This embodiment provides a solar cell, whose main structure is the same as that in Embodiment 1, and the preparation method includes the following steps: S1: Double-sided texturing of the N-type silicon substrate.

[0099] The N-type silicon substrate was texturized on both sides to remove metallic impurities and organic contaminants from its surface. The texturing time was 420 seconds at a temperature of 90°C. The texturing solution used included alkali, a texturing additive, and water. The concentration of alkali (NaOH) in the texturing solution was 0.2 wt%, and the concentration of the texturing additive was 0.02 wt%.

[0100] S2: Boron diffusive oxidation.

[0101] P-type silicon substrates are formed on the front side of an N-type silicon substrate by boron diffusion. + Emitter. A BSG layer is formed on the front side and the edge of the back side of the N-type silicon substrate through an oxidation process.

[0102] The boron diffusion temperature was 430℃, the diffusion time was 480s, the boron source flow rate was 220 sccm, the oxygen flow rate was 600 sccm, and the nitrogen flow rate was 1980 sccm. After boron diffusion, the sample underwent a propulsion process followed by high-temperature oxidation. The propulsion temperature was 980℃, and the propulsion time was 1170s. The oxidation temperature was 1030℃, and the oxidation time was 3770s. The boron source was BCl3.

[0103] S3: Remove BSG and alkali polishing.

[0104] The boron-expanded and oxidized silicon substrate undergoes a backside BSG removal process. The backside of the BSG-removed N-type silicon substrate is then subjected to alkaline polishing to remove the naturally formed oxide layer on the backside of the N-type silicon substrate.

[0105] BSG removal was performed using a 7wt% HF aqueous solution in a chain cleaning process for 100 seconds. Alkali polishing lasted 150 seconds at a temperature of 70°C. The alkali polishing solution consisted of alkali, an alkali polishing additive, and water. Specifically, the concentration of alkali (NaOH) in the alkali polishing solution was 0.1wt%, and the concentration of the alkali polishing additive was 0.02wt%.

[0106] S4: LPCVD and phosphorus diffusion.

[0107] A tunneling oxide layer and a doped polycrystalline silicon layer are deposited on the silicon substrate after BSG removal and alkaline polishing. An intrinsic amorphous silicon layer is first prepared on the surface of the tunneling oxide layer, and then the intrinsic amorphous silicon layer is subjected to phosphorus doping treatment to convert the amorphous silicon into polycrystalline silicon, thus forming a doped polycrystalline silicon layer.

[0108] The preparation conditions for the tunneling oxide layer include: deposition temperature of 550℃, oxygen purging time of 250s, and oxygen curing time of 750s. The preparation conditions for the intrinsic amorphous silicon layer include: temperature of 550℃ and reaction time of 2000s. The phosphorus doping treatment conditions include: deposition temperature of 590℃, time of 1000s, phosphorus source flow rate of 1200sccm, and oxygen flow rate of 30sccm. The phosphorus source is POCl3.

[0109] The conditions for converting amorphous silicon into polycrystalline silicon include: a driving temperature of 780℃ and a time of 1060s; and an oxidation temperature of 880℃ and a time of 1000s.

[0110] S5: Backside graphic design.

[0111] A green laser was used to pattern the PSG (phosphorus-dilated phosphorus photopolymer) in the non-metallic region on the back side of the phosphorus-dilated silicon substrate, thereby vaporizing or loosening it. A large rectangular spot with dimensions of 100 μm × 200 μm was used, with 10% overlap in both the X and Y axes.

[0112] S6: Go to PSG and RCA After the back side is patterned, the front side is first de-PSG, and then the tunneling oxide layer and doped polysilicon layer on the front side are removed by RCA. At the same time, the tunneling oxide layer and doped polysilicon layer in the non-metallic area on the back side are removed.

[0113] Removing PSG from the front side of an N-type silicon substrate may include: chain cleaning for 100 seconds using a 9wt% HF aqueous solution.

[0114] The cleaning solution used for RCA cleaning includes alkali, plating remover, and water. The concentration of alkali in the cleaning solution is 0.1 wt%, and the concentration of plating remover is 0.15 wt%. By mass percentage, the plating remover contains 1 wt% sodium benzoate, 1 wt% surfactant, 5 wt% wetting agent, 0.5 wt% sodium citrate, and the balance is water. The RCA cleaning time is 300 seconds, and the temperature is 75°C.

[0115] S7: Double-sided ALD.

[0116] After RCA cleaning, aluminum oxide was deposited on both sides of the silicon substrate to form a passivation layer with a thickness of 2nm.

[0117] S8: Double-sided coating.

[0118] The silicon substrate after double-sided ALD treatment is subjected to double-sided coating treatment. Specifically, silicon nitride composite layers are deposited on the front and back sides to form anti-reflection and passivation films.

[0119] S9: Screen printing.

[0120] The double-sided coated silicon substrate is screen-printed. The positive electrode structure is formed using silver-aluminum paste on the front side, and the negative electrode structure is formed using silver paste on the back side. Then, laser-assisted sintering technology is used to connect the electrodes to the battery substrate.

[0121] Example 3 This embodiment provides a solar cell, whose main structure is the same as that in Embodiment 1, and the preparation method includes the following steps: S1: Double-sided texturing of the N-type silicon substrate.

[0122] The N-type silicon substrate was texturized on both sides to remove metallic impurities and organic contaminants from its surface. The texturing time was 460 seconds at 70°C. The texturing solution used included alkali, a texturing additive, and water. The concentration of alkali (NaOH) in the texturing solution was 0.8 wt%, and the concentration of the texturing additive was 0.18 wt%.

[0123] S2: Boron diffusive oxidation.

[0124] P-type silicon substrates are formed on the front side of an N-type silicon substrate by boron diffusion. +Emitter. A BSG layer is formed on the front side and the edge of the back side of the N-type silicon substrate through an oxidation process.

[0125] The boron diffusion temperature was 480℃, the diffusion time was 420s, the boron source flow rate was 260sccm, the oxygen flow rate was 640sccm, and the nitrogen flow rate was 2020sccm. After boron diffusion, the sample underwent a propulsion process followed by high-temperature oxidation. The propulsion temperature was 1020℃, and the propulsion time was 1130s. The oxidation temperature was 1070℃, and the oxidation time was 3730s. The boron source was BCl3.

[0126] S3: Remove BSG and alkali polishing.

[0127] The boron-expanded and oxidized silicon substrate undergoes a backside BSG removal process. The backside of the BSG-removed N-type silicon substrate is then subjected to alkaline polishing to remove the naturally formed oxide layer on the backside of the N-type silicon substrate.

[0128] BSG removal involved a chain cleaning process using a 13wt% HF aqueous solution for 60 seconds. Alkaline polishing was performed for 250 seconds at a temperature of 50°C. The alkaline polishing solution consisted of alkali, an alkaline polishing additive, and water. Specifically, the concentration of alkali (NaOH) in the alkaline polishing solution was 0.3wt%, and the concentration of the alkaline polishing additive was 0.18wt%.

[0129] S4: LPCVD and phosphorus diffusion.

[0130] A tunneling oxide layer and a doped polycrystalline silicon layer are deposited on the silicon substrate after BSG removal and alkaline polishing. An intrinsic amorphous silicon layer is first prepared on the surface of the tunneling oxide layer, and then the intrinsic amorphous silicon layer is subjected to phosphorus doping treatment to convert the amorphous silicon into polycrystalline silicon, thus forming a doped polycrystalline silicon layer.

[0131] The preparation conditions for the tunneling oxide layer include: deposition temperature of 650℃, oxygen purging time of 350s, and oxygen curing time of 350s. The preparation conditions for the intrinsic amorphous silicon layer include: temperature of 650℃ and reaction time of 1600s. The phosphorus doping treatment conditions include: deposition temperature of 990℃, time of 600s, phosphorus source flow rate of 1600 sccm, and oxygen flow rate of 70 sccm. The phosphorus source is POCl3.

[0132] The conditions for converting amorphous silicon into polycrystalline silicon include: a driving temperature of 880℃ and a time of 860s; and an oxidation temperature of 880℃ and a time of 800s.

[0133] S5: Backside graphic design.

[0134] A green-skin laser was used to pattern the PSG (phosphorus-dilated phosphorus spores) in the non-metallic region on the back side of the phosphorus-dilated silicon substrate, thereby vaporizing or loosening it. A large rectangular spot with dimensions of 200 μm × 100 μm was used, with 90% overlap in both the X and Y axes.

[0135] S6: Go to PSG and RCA After the back side is patterned, the front side is first de-PSG, and then the tunneling oxide layer and doped polysilicon layer on the front side are removed by RCA. At the same time, the tunneling oxide layer and doped polysilicon layer in the non-metallic area on the back side are removed.

[0136] Removing PSG from the front side of an N-type silicon substrate may include: chain cleaning for 60 seconds using a 15wt% HF aqueous solution.

[0137] The cleaning solution used for RCA cleaning includes alkali, plating remover, and water. The concentration of alkali in the cleaning solution is 0.3 wt%, and the concentration of plating remover is 0.25 wt%. By mass percentage, the plating remover contains 2 wt% sodium benzoate, 3 wt% surfactant, 7 wt% wetting agent, 2 wt% sodium citrate, and the balance is water. The RCA cleaning time is 400 seconds, and the temperature is 55°C.

[0138] S7: Double-sided ALD.

[0139] After RCA cleaning, aluminum oxide was deposited on both sides of the silicon substrate to form a passivation layer with a thickness of 6 nm.

[0140] S8: Double-sided coating.

[0141] The silicon substrate after double-sided ALD treatment is subjected to double-sided coating treatment. Specifically, silicon nitride composite layers are deposited on the front and back sides to form anti-reflection and passivation films.

[0142] S9: Screen printing.

[0143] The double-sided coated silicon substrate is screen-printed. The positive electrode structure is formed using silver-aluminum paste on the front side, and the negative electrode structure is formed using silver paste on the back side. Then, laser-assisted sintering technology is used to connect the electrodes to the battery substrate.

[0144] Example 4 The difference between this embodiment and Embodiment 1 is that the concentration of the plating remover additive in the cleaning solution is 0.15 wt%.

[0145] Example 5 The difference between this embodiment and Embodiment 1 is that the concentration of the de-plating additive in the cleaning solution is 0.18 wt%.

[0146] Example 6 The difference between this embodiment and Embodiment 1 is that the concentration of the plating remover additive in the cleaning solution is 0.22 wt%.

[0147] Example 7 The difference between this embodiment and Embodiment 1 is that the concentration of the de-plating additive in the cleaning solution is 0.25 wt%.

[0148] Example 8 The difference between this embodiment and Embodiment 1 is that the surfactant is replaced with fatty alcohol polyoxyethylene ether.

[0149] Example 9 The difference between this embodiment and Embodiment 1 is that the wetting agent is replaced with alkyl-modified polysiloxane.

[0150] Comparative Example 1 The difference between this comparative example and Example 1 is that the concentration of the de-plating additive in the cleaning solution is 0.1 wt%.

[0151] Comparative Example 2 The difference between this comparative example and Example 1 is that the concentration of the de-plating additive in the cleaning solution is 0.3 wt%.

[0152] Comparative Example 3 The difference between this comparative example and Example 1 is that the de-coating additive does not contain the directional components (sodium benzoate and sodium citrate), which are replaced by water.

[0153] Comparative Example 4 The difference between this comparative example and Example 1 is that the content of sodium benzoate in the de-coating additive is 0.05 wt%.

[0154] Comparative Example 5 The difference between this comparative example and Example 1 is that the sodium benzoate content in the de-coating additive is 2.5 wt%.

[0155] Comparative Example 6 The difference between this comparative example and Example 1 is that the surfactant content in the de-coating additive is 0.5 wt%.

[0156] Comparative Example 7 The difference between this comparative example and Example 1 is that the surfactant content in the de-coating additive is 4 wt%.

[0157] Comparative Example 8 The difference between this comparative example and Example 1 is that the content of wetting agent in the de-coating additive is 4 wt%.

[0158] Comparative Example 9 The difference between this comparative example and Example 1 is that the content of wetting agent in the de-coating additive is 8 wt%.

[0159] Comparative Example 10 The difference between this comparative example and Example 1 is that the content of sodium citrate in the de-coating additive is 3 wt%.

[0160] Test case The solar cells prepared in Examples 1-9 and Comparative Examples 1-10 were compared, and the results are shown in Table 1. The tilt angle was measured using an Olympus microscope, and the other photoelectric properties were measured using an IV sorter.

[0161] Taking the solar cells prepared in Example 1 and Comparative Example 1 as examples, the schematic diagrams of the inclination angles of the corrosion steps are shown below. Figure 2 and Figure 3 As shown.

[0162] Table 1 Comparison Results

[0163] As can be seen from Table 1, the solar cells prepared in Examples 1-9 of this disclosure have better photoelectric conversion efficiency, as well as better overall performance in terms of open-circuit voltage, short-circuit current and fill factor compared with the solar cells prepared in Comparative Examples 1-10.

[0164] Examples 1, 4-7, and Comparative Examples 1-2 show that when the concentration of the de-coating additive in the cleaning solution is less than 0.15 wt% or greater than 0.25 wt%, the sidewall tilt angle of the corrosion step becomes too small or too large, which is detrimental to improving the passivation effect of the solar cell and thus leads to a deterioration in the photoelectric performance of the solar cell. A concentration of the de-coating additive in the cleaning solution of 0.18 wt% to 0.22 wt% results in a more suitable sidewall tilt angle of the corrosion step compared to other conditions within the range of 0.15 wt% to 0.25 wt%, thus better improving the photoelectric performance of the solar cell.

[0165] As can be seen from Examples 1 and Comparative Examples 3-10, improper composition of the de-coating additive can also lead to a deterioration in the photoelectric performance of the prepared solar cell.

[0166] In summary, this disclosure uses a specific concentration and composition of de-coating additives during the RCA cleaning process to make the corrosion steps formed at the junction of the metal and non-metal regions of the passivation contact structure have an inclination angle of 40° to 60°, making the transition between the non-metal and metal regions smoother and more conducive to the uniformity of the subsequent passivation film and the transport of charge carriers on the back side, thereby effectively improving the passivation level and photoelectric performance of the solar cell.

[0167] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A solar cell, characterized in that, The back of the solar cell has a passivation contact structure only at the location corresponding to the non-metallic area. The passivation contact structure forms a corrosion step at the junction of the metallic and non-metallic areas, and the sidewall of the corrosion step has an inclination angle of 40° to 60°.

2. The solar cell according to claim 1, characterized in that, The sidewalls of the corrosion step have an inclination angle of 42.6° to 56.8°.

3. The solar cell according to claim 1 or 2, characterized in that, The solar cell includes an N-type silicon substrate, and the front side of the N-type silicon substrate includes P-type silicon substrates from the inside to the outside. + The N-type silicon substrate has an emitter, a front passivation layer, a front anti-reflection film, and a metal electrode. The back side of the N-type silicon substrate has a passivation contact structure at the position corresponding to the non-metallic region. The passivation contact structure includes, from the inside to the outside, a tunneling oxide layer, a doped polysilicon layer, a back passivation layer, and a back anti-reflection film. The back side of the N-type silicon substrate has a metal electrode at the position corresponding to the metal region.

4. A method for preparing a solar cell according to any one of claims 1 to 3, characterized in that, Includes the following steps: The N-type silicon substrate is subjected to double-sided texturing, boron diffusion and oxidation, BSG removal and alkaline polishing, LPCVD and phosphorus diffusion, and back-side patterning; the PSG on the front side of the N-type silicon substrate is removed, and the tunneling oxide layer and doped polysilicon layer on the corresponding metal region on the back side of the N-type silicon substrate are removed by RCA cleaning. The cleaning solution used for RCA cleaning includes alkali, decoupling additive, and water; the decoupling additive includes aromatic carboxylate complexing agents, surfactants, wetting agents, organic acid salt pH buffers, and water; the concentration of the decoupling additive in the cleaning solution is 0.15wt%~0.25wt%.

5. The preparation method according to claim 4, characterized in that, The concentration of the de-coating additive in the cleaning solution is 0.18wt%~0.22wt%.

6. The preparation method according to claim 4, characterized in that, The concentration of the alkali in the cleaning solution is 0.1wt%~0.3wt%.

7. The preparation method according to any one of claims 4 to 6, characterized in that, By mass percentage, the de-coating additive contains 1wt% to 2wt% of the aromatic carboxylate complexing agent, 1wt% to 3wt% of the surfactant, 5wt% to 7wt% of the wetting agent, ≤2wt% of the organic acid salt pH buffer, and the balance is water.

8. The preparation method according to any one of claims 4 to 6, characterized in that, The aromatic carboxylate complexing agent includes at least one of sodium benzoate, ammonium benzoate, phthalate and salicylate; And / or, the surfactant comprises at least one of dodecyl dimethyl betaine, fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sulfate, and alkylbenzene sulfonate; And / or, the wetting agent includes at least one of polyether-modified siloxane, alkyl-modified polysiloxane, and gemynyl alcohol; And / or, the organic acid salt pH buffer includes at least one of sodium citrate, potassium citrate, sodium ethylenediaminetetraacetate, and hydroxyethylidene diphosphonic acid.

9. The preparation method according to any one of claims 4 to 6, characterized in that, The RCA cleaning time is 300s~400s, and the temperature is 55℃~75℃.

10. The preparation method according to claim 4, characterized in that, After RCA cleaning, the process also includes double-sided ALD, double-sided coating, and screen printing.

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