Heavy doping back contact battery and preparation method thereof

Abstract

The invention discloses a heavily doped back contact battery and a preparation method thereof, which can avoid the problems of doped atom volatilization, transverse diffusion and pollution in the traditional high-temperature diffusion and ensure the consistency and repeatability of doping distribution by depositing a doping mask containing boron or phosphorus and combining laser selective doping to accurately control the doping position and concentration. According to the method, fine patterning can be achieved, the process adaptability is high, and the doping design can be flexibly adjusted without changing the basic process. By performing effective secondary doping on the polycrystalline silicon or amorphous silicon film, a high-quality p-n junction is formed, the carrier collection efficiency is remarkably improved, the recombination loss is reduced, and the cell conversion efficiency is improved. Compared with traditional doping sources such as borosilicate glass, the method has the advantages that impurity pollution is reduced, long-time high-temperature treatment is not needed, stripping, cracking and other structural failures caused by thermal expansion mismatch are effectively avoided, and the electrical performance and long-term reliability of the device are improved.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and more specifically, to a heavily doped back contact cell and its preparation method. Background Technology

[0002] In the manufacturing process of back-contact solar cells, selective doping is a key step in achieving efficient carrier collection and reducing recombination losses. Currently, the industry commonly uses doped silicon dioxide or boron-doped silicon glass (BSG) as doping sources, and introduces dopant atoms (such as phosphorus and boron) into the semiconductor substrate through a high-temperature diffusion process to form the desired doped region.

[0003] However, the aforementioned traditional doping sources have significant technical drawbacks in practical applications. On the one hand, during high-temperature heat treatment, the doped atoms in doped silicon dioxide are prone to uncontrollable thermal diffusion and volatilization, making it difficult to precisely control the doping concentration, affecting the consistency and repeatability of the doping distribution, and limiting the selectivity of subsequent etching, making it difficult to adapt to fine processes. On the other hand, although borosilicate glass has a certain doping capability, its doped atom release behavior lacks good controllability and has poor chemical stability. Under high-temperature environments, it is prone to side reactions with the surrounding medium, causing impurity contamination. In addition, the large mismatch in the coefficient of thermal expansion between borosilicate glass and silicon substrate makes it prone to structural failures such as peeling and cracking during high-temperature processes, severely restricting the electrical performance and long-term reliability of devices. Summary of the Invention

[0004] This application provides a heavily doped back contact battery and its preparation method to improve the above-mentioned defects.

[0005] The embodiments of this application are implemented as follows: In a first aspect, the present invention provides a method for preparing a heavily doped back contact battery, comprising: Silicon wafer pretreatment: The silicon wafers are resistivity screened and their back sides are cleaned and surface pretreated; One-stage thin film deposition: depositing a polycrystalline silicon thin film or an amorphous silicon thin film on the back side of a silicon wafer; Boron diffusion and patterning: Boron diffusion, annealing, and patterning of silicon wafers; Boron doping deposition and laser processing: A boron-containing mask is deposited on the back of a silicon wafer, followed by selective doping using a laser; Secondary thin film deposition: depositing polycrystalline silicon thin films or amorphous silicon thin films on the back side of a silicon wafer; Phosphorus diffusion and patterning: Phosphorus diffusion, annealing, and patterning of silicon wafers; Phosphorus doping deposition and laser processing: Phosphorus-doped mask deposition is performed on the back of the silicon wafer, followed by selective doping using a laser.

[0006] In an optional embodiment, in the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, the mask comprises one or more of silicon nitride, silicon carbide, and hafnium oxide.

[0007] In an optional embodiment, in the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, a high-density plasma chemical vapor deposition (PDCVD) apparatus is used to deposit a boron-containing silicon nitride mask using silane, ammonia, and borane as reactive gases, or to deposit a phosphorus-containing silicon nitride mask using silane, ammonia, and phosphine as reactive gases, followed by selective doping using an infrared continuous laser.

[0008] In an optional embodiment, in the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, the volume ratio of borane or phosphine to silane is 0.1-500, and the radio frequency power density during the deposition process is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 200-500℃, the time is 10-100 min, and the thickness of the deposited boron- or phosphorus-doped silicon nitride mask is 10-100 nm. The power of the infrared continuous laser is 50-200W, and the selective doping width is 1-40μm.

[0009] In an optional embodiment, after the boron doping deposition and laser processing steps and between the secondary thin film deposition step, the method further includes: Cleaning and tunneling oxidation: RCA cleaning of silicon wafers and deposition of tunneling oxide film.

[0010] In an optional implementation, during the cleaning and tunneling oxidation steps: RCA cleaning includes: first, cleaning the silicon wafer with a mixed HF / HNO3 solution, followed by a second cleaning with KOH. The ratio of HF, HNO3, and H2O in the HF / HNO3 solution is 1:3:5 to 1:5:8. The temperature of the first cleaning is 10-60℃, and the time is 60-300s. The concentration of the KOH solution is 1-2.5wt%, and the reaction time of the second cleaning is 600-1200s, and the temperature is 65-85℃. The deposition of tunneling oxide films includes: high-density plasma chemical vapor deposition, in which oxygen and silane are used as process gases, the silane to oxygen flow ratio is 1:10 to 1:20, and the radio frequency power density is 0.5-20 mW / cm³. 2The pressure is 0.2-50 mbar, the temperature is 200℃-500℃, and the time is 1-10 min, resulting in a tunneling oxide film with a thickness of 1-2 nm.

[0011] In an optional embodiment, in the first or second thin film deposition step, one or more of high-density plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition, or physical vapor deposition are used to form a polycrystalline silicon thin film or an amorphous silicon thin film on the back side of the silicon wafer. The process gas uses a mixture of hydrogen, silane, and borane or phosphine, with a hydrogen to silane volume ratio of 0.1-500 and a hydrogen to borane or phosphine volume ratio of 0.1-500. The radio frequency power density is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 30℃-500℃, the time is 10-100 min, and the thickness of the deposited film is 10-300 nm.

[0012] In an optional embodiment, during the boron or phosphorus diffusion and patterning steps, the silicon wafer is annealed and crystallized using an annealing furnace. The annealing atmosphere is nitrogen or argon, with a flow rate of 2000-9000 sccm; the annealing temperature is 700-1080°C, and the time is 10-90 min. Patterning distinguishes between etched and non-etched areas. Patterning processes include one or more of screen printing, laser etching, and photolithography. In laser etching, the laser power is 200-1000W and the laser spot size is 30×30-300×300μm. In photolithography, a dry photoresist film is used as a mask and infrared light is used as the exposure light source.

[0013] In an optional embodiment, after the phosphorus doping deposition and laser processing steps, the method further includes: Surface treatment and electrode fabrication: acid etching, texturing, deposition of antireflective film, and grid line printing on silicon wafers.

[0014] Secondly, the present invention provides a heavily doped back contact battery, which is manufactured using the preparation method of a heavily doped back contact battery described in any of the foregoing embodiments.

[0015] This embodiment utilizes a deposition-based doping mask combined with laser-selective doping to precisely control the position and concentration of doped atoms, avoiding the uncontrolled diffusion and volatilization of doped atoms in traditional high-temperature diffusion processes, thus ensuring the consistency and repeatability of the doping distribution. Laser-selective doping technology enables fine patterning, giving the fabrication method better process adaptability and allowing adjustments to the design of the doped region without altering the basic process flow, improving production flexibility. Furthermore, by precisely controlling the boron and phosphorus doping processes, effective secondary doping of polycrystalline or amorphous silicon thin films is achieved, which helps form high-quality pn junctions, effectively improving carrier collection efficiency, reducing recombination losses, and further enhancing the energy conversion efficiency of back-contact solar cells. Compared to traditional doping sources such as borosilicate glass, laser-selective doping technology reduces the risk of impurity contamination caused by chemical reactions. Moreover, since it eliminates the need for long-term high-temperature heat treatment, it reduces the risk of structural failures such as peeling and cracking caused by differences in the thermal expansion coefficients between materials, contributing to improved device electrical performance and long-term reliability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application 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.

[0017] Figure 1 This is a flowchart illustrating the preparation method of a heavily doped back contact battery according to an embodiment of this application. Detailed Implementation

[0018] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0019] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0020] In these embodiments, unless otherwise specified, the parts and amounts are all by weight.

[0021] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0022] refer to Figure 1 This application discloses a method for preparing a heavily doped back contact battery, comprising the following steps: Silicon wafer pretreatment: The silicon wafers are resistivity screened and their back sides are cleaned and surface pretreated; One-stage thin film deposition: depositing a polycrystalline silicon thin film or an amorphous silicon thin film on the back side of a silicon wafer; Boron diffusion and patterning: Boron diffusion, annealing, and patterning of silicon wafers; Boron doping deposition and laser processing: A boron-containing mask is deposited on the back of a silicon wafer, followed by selective doping using a laser; Secondary thin film deposition: depositing polycrystalline silicon thin films or amorphous silicon thin films on the back side of a silicon wafer; Phosphorus diffusion and patterning: Phosphorus diffusion, annealing, and patterning of silicon wafers; Phosphorus doping deposition and laser processing: Phosphorus-doped mask deposition is performed on the back of the silicon wafer, followed by selective doping using a laser.

[0023] This approach, combining deposition of a doping mask with laser-selective doping, allows for precise control of the position and concentration of doped atoms. This avoids the uncontrolled diffusion and volatilization issues inherent in traditional high-temperature diffusion processes, ensuring consistent and repeatable doping distribution. Laser-selective doping enables fine patterning, improving process adaptability and allowing adjustments to the doped region design without altering the basic process flow, thus enhancing production flexibility. Furthermore, precise control of boron and phosphorus doping enables effective secondary doping of polycrystalline or amorphous silicon films, facilitating the formation of high-quality pn junctions. This significantly improves carrier collection efficiency, reduces recombination losses, and further enhances the energy conversion efficiency of back-contact solar cells. Compared to traditional doping sources like borosilicate glass, laser-selective doping reduces the risk of impurity contamination from chemical reactions. Moreover, the elimination of the need for prolonged high-temperature heat treatment lowers the risk of structural failures such as peeling and cracking caused by differences in thermal expansion coefficients between materials, contributing to improved device electrical performance and long-term reliability.

[0024] In summary, the preparation method of this embodiment not only overcomes the main defects of traditional doping technology, but also significantly improves the overall performance of back contact solar cells.

[0025] In this embodiment, in the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, the mask includes one or more of silicon nitride, silicon carbide and hafnium oxide, and laser selective doping can be performed according to the selective doping of N / P type elements.

[0026] In this way, because silicon nitride, silicon carbide, and hafnium oxide all possess high melting points, good thermal stability, and chemical inertness, they are less likely to decompose or undergo side reactions with the silicon substrate during high-temperature laser processing. This effectively avoids the problem of traditional doping sources (such as borosilicate glass) releasing impurities or contaminating interfaces at high temperatures, thus ensuring the purity of the doped region and the reliability of the device. Moreover, silicon nitride, silicon carbide, and hafnium oxide can be introduced into their structures and stably stored as dopants such as boron or phosphorus through process control. Under the local heating effect of laser, the controllable release and directional diffusion of dopant atoms can be achieved, significantly improving doping efficiency and depth control precision, which is conducive to forming a steep and uniform doping distribution. In addition, silicon nitride, silicon carbide, and hafnium oxide have excellent etching selectivity with silicon or polycrystalline silicon, which facilitates the preservation of precise doping windows in subsequent patterning processes. At the same time, they themselves have good mechanical strength and resistance to laser ablation, which helps maintain the integrity of the pattern during laser processing and supports the construction of micron or even submicron level fine doped structures.

[0027] It should be noted that the reason for using a boron- or phosphorus-doped mask for deposition followed by laser selective doping is that it allows for: 1. Reduce equipment corrosion and laser energy consumption, and optimize process compatibility: Borosilicate glass (BSG) formed by thermal diffusion has a low boron concentration, requiring a high-power laser for laser doping and easily causing surface damage. However, boron-doped silicon nitride deposition can reduce the laser power requirement and minimize silicon wafer damage.

[0028] Boron-doped silicon nitride (SiN) exhibits high stability and, when deposited, serves as a boron source, avoiding the formation of corrosive byproducts associated with traditional boron sources, thus protecting the equipment from the outset. Simultaneously, the uniform and controllable boron distribution within SiN, coupled with SiN's excellent laser absorption characteristics, allows the SiN layer to efficiently absorb laser energy and transfer it to boron atoms during laser irradiation. This energy causes boron atoms to detach from the SiN lattice and diffuse into the silicon substrate. This synergistic effect significantly reduces the power required for laser doping, prevents damage to the textured surface of silicon wafers from high-power lasers, eliminates the need for complex anti-corrosion modifications to equipment, and offers better compatibility with existing production lines.

[0029] 2. Precisely forming high- and low-doped junctions reduces contact resistance and recombination losses: While traditional techniques such as secondary boron diffusion can achieve doping, they are cumbersome, costly, and have low precision in the doped region, which can easily lead to increased carrier recombination losses. However, boron-doped silicon nitride deposition combined with laser selective doping can precisely form heavily doped regions in the electrode contact area while keeping lightly doped regions in the non-contact area. This reduces contact resistance, minimizes interfacial recombination, and improves the adhesion between the electrode and the substrate.

[0030] The laser possesses high directionality and high energy concentration, allowing selective irradiation of a predetermined area contacting the electrode. The laser energy causes a rapid increase in the local temperature of the irradiated area, enabling boron atoms in the boron-doped silicon nitride to gain sufficient kinetic energy and quickly diffuse into the silicon substrate, resulting in a carrier concentration as high as 8.08 × 10²¹ cm⁻¹. - A heavily doped P++ layer (³) is formed in the PN junction; the un-illuminated boron-containing silicon nitride layer acts as a passivation layer, maintaining the lightly doped state. The heavily doped and lightly doped regions form a high-low junction, increasing the built-in potential of the PN junction and reducing carrier recombination. Simultaneously, the heavily doped region increases the carrier concentration on the silicon substrate, improving the electrical contact between the metal and silicon and significantly reducing contact resistance. Furthermore, the lattice structure of the doped regions, after laser irradiation, bonds more tightly to the electrode metal, enhancing electrode adhesion.

[0031] 3. Improve doping uniformity, reduce defects, and optimize passivation effect: Existing CVD source layer deposition techniques are prone to boron defects, and the surface boron concentration is difficult to control, affecting the passivation effect in non-laser regions. However, laser selective doping after boron-doped silicon nitride deposition can reduce boron defects, lower the surface boron concentration in non-doped regions, improve overall passivation performance, and help improve device efficiency.

[0032] In the boron-doped silicon nitride deposition process, the boron doping amount and film uniformity can be precisely controlled through process parameters, providing a uniform boron source foundation for subsequent doping. During laser selective doping, energy is applied only to specific regions, avoiding the disordered diffusion of boron atoms and defect generation caused by global high-temperature processing. Simultaneously, silicon nitride itself possesses excellent passivation properties; in areas not irradiated by the laser, the boron-doped silicon nitride layer can hinder carrier recombination on the surface. Furthermore, nitrogen atoms in silicon nitride can combine with dangling bonds on the silicon substrate surface, further optimizing the passivation effect. In addition, the binding characteristics of boron atoms with silicon nitride can suppress excessive boron atom aggregation, reduce boron defects, and avoid recombination losses caused by excessively high boron concentrations in undoped areas.

[0033] In detail, the silicon wafer pretreatment process involves resistivity screening followed by etching and alkaline polishing on the back side of the silicon wafer.

[0034] In this process, after screening silicon wafers by resistivity using a silicon wafer sorting machine, the silicon wafers are alkaline polished using a KOH solution with a concentration of 1-3wt% at a reaction temperature of 60-85℃ and a reaction time of 10-40min.

[0035] In the boron-doped deposition and laser processing step or the phosphorus-doped deposition and laser processing step, the volume ratio of borane or phosphine to silane is 0.1-500, and the radio frequency power density during the deposition process is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 200-500℃, the time is 10-100 min, and the thickness of the deposited boron or phosphorus-doped silicon nitride mask is 10-100 nm; the power of the infrared continuous laser is 50-200 W, and the selective doping width is 1-40 μm.

[0036] When the ammonia / silane ratio is 0.1 / 500, the silane content is extremely high, while the ammonia content is severely insufficient. The film will exhibit strong silicon-rich characteristics, with a significantly increased refractive index and a substantial decrease in electrical insulation properties, failing to provide effective passivation. Simultaneously, insufficient nitrogen content leads to an increase in silicon nitride lattice defects, resulting in disordered phosphorus atom distribution in the film. This leads to poor phosphorus diffusion uniformity during subsequent laser doping, making it difficult to form a stable N-type doped region.

[0037] If the ammonia / silane ratio is less than 0.1, the relative proportion of silane is higher, exacerbating the silicon enrichment phenomenon. The film structure is loose, with extremely low density, making it prone to defects such as pinholes and cracks, resulting in extremely poor mechanical strength and severely insufficient adhesion. Furthermore, the lack of nitrogen atoms weakens the binding effect on phosphorus atoms, causing some phosphorus atoms to easily escape during deposition, reducing doping efficiency. Consequently, the film is prone to detachment during subsequent laser processing, making effective doping impossible.

[0038] If the ammonia / silane ratio is greater than 500: ammonia is excessive while silane is present in very low proportions. Insufficient silicon atoms in the reaction system lead to a sharp drop in film growth rate, making it difficult to form a continuous and complete silicon nitride film. Excessive ammonia easily enriches the film with nitrogen, resulting in an excessively low refractive index and failure of antireflection properties (unsuitable for applications requiring high optical performance, such as solar cells). Simultaneously, a nitrogen-rich environment inhibits phosphorus doping, causing the phosphorus concentration in the film to fall below the effective range of 1%, making it difficult for phosphorus to diffuse into the silicon substrate and form a qualified PN junction during subsequent annealing or laser doping.

[0039] Excessive RF power (e.g., exceeding 20mW / cm) 2 On the one hand, it can cause the plasma density in the reaction chamber to be too high, which can easily lead to "arson" and damage the uniformity of the silicon nitride film. It may also etch the surface of the silicon substrate, causing damage to the silicon wafer. On the other hand, excessively high energy can break the stable combination of phosphorus-nitrogen and silicon-nitrogen chemical bonds, causing phosphorus atoms to escape prematurely and increasing the internal stress of the film sharply, which can easily lead to cracking and peeling later.

[0040] The radio frequency power is too low (e.g., less than 0.5mW / cm). 2 It is difficult to ionize ammonia, silane, and phosphine to form a stable plasma, resulting in incomplete reactions and extremely slow film growth rates. Furthermore, the resulting films have loose structures, low density, and poor adhesion to the silicon substrate. Simultaneously, insufficient plasma energy fails to drive phosphorus atoms to uniformly integrate into the silicon nitride lattice, leading to low and uneven phosphorus doping concentration, which cannot meet the source layer requirements for subsequent doping.

[0041] Excessive reaction pressure (e.g., exceeding 50 mbar) slows down gas diffusion within the reaction chamber, leading to uneven gas mixing in different areas and significant differences in film thickness and composition, thus disrupting the uniformity of phosphorus doping. Furthermore, the high-pressure environment can cause byproducts generated during the reaction to become trapped and difficult to remove. These impurities can form defects in the film, reducing its electrical and mechanical properties; they may also cause pinholes and other flaws, affecting the passivation effect.

[0042] If the reaction pressure is too low (e.g., less than 0.2 mbar), the probability of gas molecule collisions decreases, plasma stability is poor, and it is difficult to sustain the deposition reaction. The resulting film is prone to discontinuous breaks, making it impossible to form a complete film layer; moreover, the free path of phosphorus atoms increases under low pressure, making them prone to escape from the reaction region, resulting in a significant decrease in doping efficiency and a phosphorus atom content in the film that is far below the target value.

[0043] Excessive deposition temperature (e.g., exceeding 500℃): The film growth rate will continuously decrease, and the high temperature will accelerate the loss of hydrogen atoms from the silicon nitride film. Hydrogen atoms are crucial for passivation performance; after hydrogen loss, the surface recombination rate increases, and the passivation effect deteriorates. At the same time, the high temperature will disrupt the bonding state between phosphorus atoms and the silicon nitride lattice, causing phosphorus atoms to aggregate and form defects. During subsequent laser doping, local phosphorus concentrations may be too high or too low. Extreme high temperatures may also cause a mismatch in the thermal expansion coefficients between the silicon substrate and the film, leading to film cracking.

[0044] Too low a deposition temperature: For example, below 200℃, the kinetic energy of the reacting molecules is insufficient, the chemical vapor deposition reaction is incomplete, the film structure is loose, the density is low, and the mechanical strength is poor. Moreover, low temperature is not conducive to the diffusion of phosphorus atoms into the silicon nitride lattice, resulting in phosphorus doping concentrated on the surface of the film with very little doping inside. During subsequent laser irradiation, the supply of phosphorus atoms is insufficient, and they cannot effectively diffuse into the depth of the silicon substrate.

[0045] Excessive deposition time: For example, exceeding 100 minutes, the film thickness will exceed the reasonable range of 10-100 nm. An excessively thick silicon nitride film will increase the energy loss during laser doping, making it difficult for the laser to penetrate the film to promote the diffusion of phosphorus atoms. It will also cause the accumulation of internal stress in the film, increasing the risk of cracking. At the same time, excessively long deposition time can easily lead to excessive accumulation of phosphorus atoms, forming local high-concentration areas, which will cause carrier recombination loss.

[0046] If the deposition time is too short, for example less than 10 minutes, the film thickness will be insufficient and a complete capping layer cannot be formed. This will not only fail to passivate and reduce reflection, but also result in insufficient phosphorus atoms during subsequent laser doping due to the thin phosphorus source layer. Consequently, a heavily doped region that meets the requirements cannot be formed on the silicon substrate, leading to increased contact resistance and decreased device performance.

[0047] Excessive laser power: For example, exceeding 200W, excessive laser energy will cause excessive melting of the silicon wafer surface, resulting in surface damage and microcracks, leading to discontinuity of the PN junction and shunting problems; at the same time, excessive power will destroy the interface structure between silicon nitride and silicon substrate, increasing the series resistance and easily causing uneven electroplating.

[0048] If the laser power is too low, for example less than 50W, it cannot provide enough energy to make phosphorus atoms detach from the silicon nitride lattice. The diffusion kinetic energy of phosphorus atoms is insufficient, the doping concentration is too low, and it is difficult to form a low-resistance selective emitter region. Moreover, the energy is not enough to melt the surface of the silicon wafer. Phosphorus atoms only stay at the interface between the thin film and the silicon substrate and cannot diffuse into the substrate, resulting in doping failure. It may also form an unpassivated edge, which becomes a high recombination site for charge carriers.

[0049] If the laser selective doping width is too small (e.g., less than 1 μm), misalignment between the metal electrode and the doped region is highly likely. Furthermore, the narrow doping region limits the total number of dopant atoms that can be implanted, potentially preventing the achievement of the critical doping concentration required for low-resistance ohmic contacts during subsequent annealing or laser activation. This leads to an increased contact barrier and increased series resistance. In addition, feature sizes <1 μm are close to the optical diffraction limit, placing extremely high demands on the laser focusing system, silicon wafer flatness, and the stability of the motion platform. Even minor disturbances can cause pattern breakage or discontinuity, significantly reducing process robustness and production line yield.

[0050] Excessive laser-selective doping width (e.g., exceeding 40 μm) requires alternating P-type and N-type doped finger regions on the back side of the back contact cell. If the width of a single doped region exceeds 40 μm, it will significantly compress the proportion of the undoped passivation region. While a wider doped region is beneficial for reducing contact resistance, its longer lateral conductive path may increase the lateral transport resistance from the photogenerated carrier generation point to the electrode, especially in regions far from the metal grid lines, resulting in uneven current collection efficiency and a reduced fill factor (FF). In back contact structures, P / N finger regions need to be closely interleaved to form a strong localized built-in electric field for efficient electron-hole separation. Excessive doping width leads to increased PN spacing, weakening the electric field strength and increasing the probability of carrier recombination, which is detrimental to achieving high efficiency.

[0051] In a single or double thin film deposition step, a polycrystalline silicon thin film or an amorphous silicon thin film is formed on the back side of a silicon wafer using one or more of high-density plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition or physical vapor deposition. The process gas uses a mixture of hydrogen, silane, and borane or phosphine, with a hydrogen to silane volume ratio of 0.1-500 and a hydrogen to borane or phosphine volume ratio of 0.1-500. The radio frequency power density is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 30℃-500℃, the time is 10-100 min, and the thickness of the deposited film is 10-300 nm.

[0052] In the boron or phosphorus diffusion and patterning steps, the silicon wafer is annealed and crystallized using an annealing furnace. The annealing atmosphere is nitrogen or argon, with a flow rate of 2000-9000 sccm. The annealing temperature is 700-1080℃, and the time is 10-90 min. For example, N2 is introduced at a temperature of 700℃-900℃ and held for 500s-7000s for annealing.

[0053] Patterning distinguishes between etched and non-etched areas. Patterning processes include one or more of screen printing, laser etching, and photolithography. In laser etching, the laser power is 200-1000W and the laser spot size is 30×30-300×300μm. In photolithography, a dry photoresist film is used as a mask and infrared light is used as the exposure light source.

[0054] The method further includes, after the boron doping deposition and laser processing steps and between the secondary thin film deposition step: Cleaning and tunneling oxidation: RCA cleaning of silicon wafers and deposition of tunneling oxide film.

[0055] In this way, if the boron-containing mask (such as boron-containing silicon nitride) undergoes partial decomposition, carbonization, or metal / particle residue under local high temperature during laser selective doping, the RCA cleaning process can efficiently remove organic matter, metal impurities, and laser-induced byproducts from the silicon wafer surface. The clean surface provides an ideal substrate for the subsequent deposition of high-quality tunneling oxide and polycrystalline silicon thin films, significantly reducing the interface state density and improving the passivation effect.

[0056] The core function of the tunneling oxide layer is to allow majority carriers (such as holes in the P-type region and electrons in the N-type region) to be transported efficiently through quantum tunneling; at the same time, it blocks minority carriers from reaching the polycrystalline silicon / metal interface with a high recombination risk, thereby achieving selective contact of carriers.

[0057] Furthermore, if secondary polycrystalline silicon or amorphous silicon films are directly deposited after laser activation of the boron-doped region, the existing P-type dopant distribution may undergo re-diffusion or deactivation, as well as interface defect regeneration, due to high temperature or plasma bombardment. In this embodiment, an ultrathin tunneling oxide layer is introduced as a "buffer / isolation layer," which can physically protect the doped region, while its excellent dielectric properties help maintain the steepness of the doping profile and electrical stability.

[0058] In the steps of cleaning and tunnel oxidation: RCA cleaning includes: firstly, cleaning the silicon wafer with a mixed HF / HNO3 solution, followed by a second cleaning with KOH. The ratio of HF, HNO3, and H2O in the HF / HNO3 solution is 1:3:5 to 1:5:8. The temperature of the first cleaning is 10-60℃, and the time is 60-300s. The concentration of the KOH solution is 1-2.5wt%, the alkaline cleaning additive is 0.05-0.10wt%, and the reaction time of the second cleaning is 600-1200s, and the temperature is 65-85℃.

[0059] The secondary cleaning can be performed under ultrasonic conditions, with an ultrasonic power of 600-1200w and a frequency of 20-80KHz. Bubbling conditions can also be added, and some surfactants can be added to the solution, such as K2SO4, SLS, DP, DBSA, SDS, or other surfactants, or Triton or OG additives can be compounded.

[0060] The deposition of tunneling oxide films includes: high-density plasma chemical vapor deposition, in which oxygen and silane are used as process gases, the silane to oxygen flow ratio is 1:10 to 1:20, and the radio frequency power density is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 200℃-500℃, and the time is 1-10 min, resulting in a tunneling oxide film with a thickness of 1-2 nm.

[0061] Following the phosphorus doping deposition and laser processing steps, the method further includes: Surface treatment and electrode fabrication: acid etching, texturing, deposition of antireflective film, and grid line printing on silicon wafers.

[0062] Thus, acid etching effectively removes the phosphosilicate glass (PSG) formed on the silicon wafer surface during phosphorus diffusion or laser doping, while avoiding the erosion of the finely formed P / N finger structure by alkaline solutions, maintaining the integrity of the back-side doping pattern. Texturing processes create micron-scale pyramids or random uneven structures on the silicon wafer surface, improving fiber reflectivity. Combined with subsequent antireflection coatings, this achieves a wide-spectrum, wide-angle light trapping effect, significantly increasing short-circuit current density. Electrodes are formed through grid line printing, allowing photovoltaic current to flow out.

[0063] The acid etching process includes: using a mixed solution of HF concentration of 3-6 wt% and HNO3 to HF solution ratio of 6-8:1, together with an HCl solution of 1-2 wt%, to acid-etch the silicon wafer to remove the back mask and front oxide layer of the silicon wafer.

[0064] Texturing includes texturing a silicon wafer using a mixed solution of alkali and texturing additives. The alkali can be KOH or NaOH, with the alkali washing solution at 1.0wt%-2.5wt% and the alkali washing additive at 0.05-0.10wt%. The reaction time is 600-1200s, and the reaction temperature is 65-85℃. The process can be performed under ultrasonic conditions with a power of 600-1200W and a frequency of 20-80kHz. Bubbling can also be added, and appropriate surfactants can be added to the solution, such as K2SO4, SLS, DP, DBSA, SDS, or other surfactants, or compounded Triton or OG additives. After cleaning and texturing, the textured surface size of the silicon wafer is 0.5μm-3.6μm.

[0065] The antireflective coating comprises: silane, nitrogen, and ammonia as process gases, with a silane to ammonia volume ratio of 1:3 to 1:10, a nitrogen to silane volume ratio of 1:1 to 10:1, a temperature of 200℃-500℃, a time of 10-60 min, a pressure of 0.2-50 mbar, and an RF power density of 0.5-20 mW / cm². 2 The thickness of the formed silicon nitride passivation film is 50-140 nm, and the refractive index of silicon nitride is 2.00-2.10.

[0066] In addition to the silicon nitride passivation film, it may also include materials such as SiO2. x AlO x SiN x O y MgF x The same film layers are formed to create a composite passivation film.

[0067] The grid line printing includes forming metal electrodes by screen printing. The front sintering temperature is 150-300℃ for 20-30 minutes, and the back sintering temperature is 180-250℃ for 20-30 minutes.

[0068] This embodiment also discloses a heavily doped back contact battery, which is prepared using the preparation method of the heavily doped back contact battery described in the above embodiment.

[0069] The following is a detailed description of the fabrication method of the heavily doped back contact cell according to the embodiments of this application: Example 1 S1. After resistivity screening of silicon wafers, the back side is etched and alkaline polished. S2. Deposit polycrystalline silicon thin film or amorphous silicon thin film on the back side of the silicon wafer; S3. Boron diffusion and annealing are performed on the silicon wafer; S4. Perform laser patterning on the silicon wafer once (P1); S5. Deposit boron-doped silicon nitride on the back side of the silicon wafer and perform laser selective doping to form P++; S6. Perform RCA cleaning on the silicon wafer; S7. Deposit a tunnel oxide film on the back side of the silicon wafer; S8. Deposit polycrystalline silicon thin film or amorphous silicon thin film on the back side of the silicon wafer; S9. Phosphorus diffusion and annealing of silicon wafers; S10, Laser secondary patterning of silicon wafer P2; S11. Phosphorus-doped silicon nitride is deposited on the back side of the silicon wafer and laser selective doping is performed to form N++. S12, Acid etching is performed on the silicon wafer; S13. Texturing the silicon wafer; S14. Apply anti-reflective coatings to the front and back sides of the silicon wafer using HDPCVD. S15. Print grid lines on the back of the silicon wafer.

[0070] In detail, in step S1, a silicon wafer sorter is used to screen the silicon wafers by resistivity. The KOH solution concentration is 1.5wt%, the reaction temperature is 70℃, and the reaction time is 28min for alkaline polishing. In step S2, a mixture of hydrogen, silane, and B2H6 from HDPCVD is used as the process gas. The volume ratio of hydrogen to silane is 10, the volume ratio of hydrogen to borane is 10, and the RF power density is 15 mW / cm². 2 The pressure was 25 mbar, the temperature was 400℃, and the time was 20 min, with a thickness of 200 nm.

[0071] The annealing in steps S3 and S9 involves crystallizing the silicon wafer using a high-temperature annealing furnace. The annealing method can be rapid thermal annealing or tubular high-temperature annealing. The annealing atmosphere is nitrogen or argon, the annealing temperature is 700-1080℃, and the annealing time is 10-90 minutes.

[0072] Steps S4 and S10 involve patterning. This distinguishes between etched and non-etched areas. Patterning processes include screen printing, laser etching, and photolithography. For example, laser etching can be used for patterning, with laser power ranging from 200-1000W and laser spot size from 30μm x 30μm to 300μm x 300μm. In photolithography, a dry photoresist film can be used as a mask, and infrared light can be used as the exposure light source.

[0073] In step S5, an HDPCVD device is used, with silane, ammonia, and borane as reactant gases. The volume ratio of ammonia to silane is 8, and the volume ratio of borane to silane is 10. The RF power density is 15 mW / cm2, the pressure is 10 mbar, the temperature is 350℃, and the time is 15 min, resulting in a thickness of 80 nm. Subsequently, selective doping is performed using an infrared continuous laser with a power of 180 W. Selective doping is performed on the non-etched area, with a selective doping width of 30 μm, forming a P++ region on the P-polysilicon.

[0074] In step S6, HF and HNO3 are first used as the main etching solution, with an HF:HNO3:H2O ratio of 1:4:8. The temperature is 25℃ and the time is 200s. An immersion process can be used to remove the mask. Subsequently, KOH is used as the main etching solution, with an alkaline washing solution of 1.5wt% and an alkaline washing additive of 0.08wt%. The reaction time is 850s and the reaction temperature is 72℃.

[0075] In step S7, HDPCVD is used, with oxygen and silane as process gases. The flow ratio of silane to oxygen is 1:13, and the RF power density is 15 mW / cm³. 2 The pressure was 20 mbar, the temperature was 400℃, and the time was 2 min. The thickness of the resulting tunneling oxide film was 1.5 nm.

[0076] In step S8, a mixture of hydrogen, silane, and phosphine is used as the process gas in HDPCVD. The volume ratio of hydrogen to silane (H2 / SiH4) is 10, the volume ratio of hydrogen to phosphine (H2 / PH3) is 10, and the RF power density is 10 mW / cm². 2 The pressure was 10 mbar, the temperature was 450℃, the time was 35 min, and the thickness was 200 nm.

[0077] In step S11, an HDPCVD device is used, with silane, ammonia, and phosphine as reactant gases. The volume ratio of ammonia to silane is 8, and the volume ratio of phosphine to silane is 10. The radio frequency power density is 15 mW / cm². 2 The pressure was 10 mbar, the temperature was 350℃, and the time was 15 min, with a thickness of 80 nm. Then, selective doping was performed using an infrared continuous laser with a power of 180 W. Selective doping was performed in the non-etched area, with a selective doping width of 30 μm, forming an n++ region in the n-polysilicon.

[0078] In step S12, the HF concentration is 3 wt%, the HNO3 to HF solution ratio is 6:1, and HCl is used for acid washing at a concentration of 1.2 wt% to remove the surface silicon nitride mask and oxide layer.

[0079] In step S13, a mixed solution of alkali and texturing additive is used to texturize the silicon wafer. The alkali is 1.0 wt% KOH solution, the alkali additive is 0.05%, the reaction time is 1000 s, the reaction temperature is 75℃, and the textured surface size is 0.5-3.6 micrometers.

[0080] In step S14, silane, nitrogen, and ammonia are used as process gases. The volume ratio of silane to ammonia is 1:8, and the volume ratio of nitrogen to silane is 10:1. The temperature is 400℃, the time is 36 minutes, the pressure is 20 mbar, and the RF power density is 12 mW / cm². 2 The resulting silicon nitride passivation film has a thickness of 80 nm and a refractive index of 2.00.

[0081] In step S15, metal electrodes are formed by screen printing. The sintering temperature of the front side is 150-300℃, and the time is 20-30 min; the sintering temperature of the back side is 180-250℃, and the time is 20-30 min, with a linewidth of 25 micrometers.

[0082] Example 2 In step S5, the volume ratio of borane to silane is 0.5, and in step S11, the volume ratio of phosphine to silane is 0.5.

[0083] In S5 and S11, the ammonia / silane volume ratio is 0.5, and the parameters for high-density plasma chemical vapor deposition are: radio frequency power density of 0.3 mW / cm³. 2 The reaction pressure was 0.1 mbar, the reaction temperature was 150℃, the deposition time was 5 min, and the laser power was 30 W.

[0084] Example 3 In step S5, the volume ratio of borane to silane is 1, and in step S11, the volume ratio of phosphine to silane is 1.

[0085] In S5 and S11, the ammonia / silane volume ratio is 1, and the parameters for high-density plasma chemical vapor deposition are: radio frequency power density of 0.5 mW / cm³. 2 The reaction pressure was 0.2 mbar, the reaction temperature was 200℃, the deposition time was 10 min, and the laser power was 50 W.

[0086] Example 4 In step S5, the volume ratio of borane to silane is 20, and in step S11, the volume ratio of phosphine to silane is 20.

[0087] In S5 and S11, the ammonia / silane volume ratio is 20, and the parameters for high-density plasma chemical vapor deposition are: radio frequency power density of 20 mW / cm³. 2 The reaction pressure was 50 mbar, the reaction temperature was 500℃, the deposition time was 110 min, and the laser power was 200 W.

[0088] Example 5 In step S5, the volume ratio of borane to silane is 25, and in step S11, the volume ratio of phosphine to silane is 25.

[0089] In S5 and S11, the ammonia / silane volume ratio is 25. The parameters for high-density plasma chemical vapor deposition are: RF power density of 0.25 mW / cm³. 2 The reaction pressure was 60 mbar, the reaction temperature was 550℃, the deposition time was 120 min, and the laser power was 250 W.

[0090] Example 6 In step S5, the volume ratio of borane to silane is 10, and in step S11, the volume ratio of phosphine to silane is 10.

[0091] In S5 and S11, the ammonia / silane volume ratio is 10. The parameters for high-density plasma chemical vapor deposition are: radio frequency power density of 15 mW / cm³. 2 The reaction pressure was 25 mbar, the reaction temperature was 400℃, the deposition time was 20 min, and the laser power was 80 W.

[0092] Comparative Example 1 Unlike Example 1, no doped silicon nitride was deposited; instead, laser selective doping was performed directly.

[0093] Comparative Example 2 Unlike Example 1, N++ formed by depositing silicon nitride is not deposited; instead, laser selective doping is performed directly.

[0094] Comparative Example 3 Unlike Example 1, P++ formed by depositing silicon nitride is not deposited; instead, laser selective doping is performed directly.

[0095] The back contact batteries prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 1 below: Table 1

[0096] As shown in the table above, Example 1 has a lifespan that is about 1000µs longer, iVoc that is 1.5mV higher, iFF that is 0.17% higher, and the battery efficiency that is made is 0.13% higher, Voc that is 1.9mV higher, Isc that is 0.01A higher, and FF that is 0.15% higher than that of Comparative Example 1.

[0097] Compared to Comparative Example 1, Comparative Example 2 has a lifespan that is about 700µs longer, an iVoc that is 1.0mV higher, an iFF that is 0.13% higher, and a battery efficiency that is 0.09% higher, an Voc that is 1.2mV higher, an Isc that is 0.01A higher, and an FF that is 0.15% higher.

[0098] Compared to Comparative Example 1, Comparative Example 3 has a lifespan that is about 300µs longer, an iVoc that is 0.8mV higher, an iFF that is 0.07% higher, a battery efficiency that is 0.05% higher, an Voc that is 0.5mV higher, an Isc that is the same, and an FF that is 0.07% higher.

[0099] It should be noted that in Example 2, the film thickness was only 3-5 nm, far below the target range, resulting in an extremely low deposition rate and discontinuous film. The boron dopant distribution was uneven, leading to poor density, easy film detachment, and a resistivity as high as 70-80 Ω. cm. Insufficient laser power prevents effective selective doping, resulting in blurred boundaries between doped and undoped regions.

[0100] In Example 3, the film thickness was 10-12 nm, meeting the lower limit requirement. The density was slightly good, but the uniformity was slightly off, and the structure was stable with no shedding. The boron doping concentration was moderate, and the resistivity was 12-15 Ω. cm, meeting the basic conductivity requirements of back-contact batteries. Laser doping exhibits good selectivity, uniform sheet resistance in the doped region, and low electrical performance parameters.

[0101] In Example 4, the film thickness was 95-100 nm, with slightly better density, slightly lower uniformity deviation, and strong adhesion between the film and the silicon substrate. At high boron doping concentrations, the resistivity was as low as 0.8-1.2 Ω. The material exhibits excellent electrical conductivity. It features sufficient laser power, precise doping depth (100-120nm), good isolation between doped and undoped regions, and low electrical performance parameters.

[0102] In Example 5, the film thickness reached 110-120 nm, exceeding the target range. Over-deposition led to stress concentration within the film, resulting in microcracks at the edges. Excessive boron doping reduced the resistivity to 0.3-0.5 Ω. However, excessive ammonia gas caused slight corrosion on the silicon substrate surface, increasing the number of defects at the film interface. Excessive laser power led to thermal damage in the doped regions, resulting in localized erosion pits, increased battery leakage current, high process costs, and unstable performance.

[0103] In Example 6, the film thickness reached the target value, exhibiting good density, uniformity, and passivation capability. With appropriate boron doping, it demonstrated excellent conductivity and a moderate resistivity of 0.8-12Ω. cm. The laser power is moderate, the FF reaches over 80%, the opening voltage is around 0.73-0.74, the efficiency is high, and the performance is stable.

[0104] In summary, when the doped silicon nitride is precisely matched with the laser etching parameters, high-efficiency (>24.6%) and high-yield TBC cells can be fabricated.

[0105] The above description is merely a specific embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a heavily doped back contact battery, characterized in that, include: Silicon wafer pretreatment: The silicon wafers are resistivity screened and their back sides are cleaned and surface pretreated; One-stage thin film deposition: depositing a polycrystalline silicon thin film or an amorphous silicon thin film on the back side of a silicon wafer; Boron diffusion and patterning: Boron diffusion, annealing, and patterning of silicon wafers; Boron doping deposition and laser processing: A boron-containing mask is deposited on the back of a silicon wafer, followed by selective doping using a laser; Secondary thin film deposition: depositing polycrystalline silicon thin films or amorphous silicon thin films on the back side of a silicon wafer; Phosphorus diffusion and patterning: Phosphorus diffusion, annealing, and patterning of silicon wafers; Phosphorus doping deposition and laser processing: Phosphorus-doped mask deposition is performed on the back of the silicon wafer, followed by selective doping using a laser.

2. The method for preparing a heavily doped back contact battery according to claim 1, characterized in that, In the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, the mask includes one or more of silicon nitride, silicon carbide, and hafnium oxide.

3. The method for preparing a heavily doped back contact battery according to claim 2, characterized in that, In the steps of boron doping deposition and laser processing or phosphorus doping deposition and laser processing, a high-density plasma chemical vapor deposition (PDCVD) device is used to deposit a boron-containing silicon nitride mask using silane, ammonia, and borane as reactive gases, or to deposit a phosphorus-containing silicon nitride mask using silane, ammonia, and phosphine as reactive gases, followed by selective doping using an infrared continuous laser.

4. The method for preparing a heavily doped back contact battery according to claim 2, characterized in that, In the boron-doped deposition and laser processing step or the phosphorus-doped deposition and laser processing step, the volume ratio of borane or phosphine to silane is 0.1-500, and the radio frequency power density during the deposition process is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 200-500℃, the time is 10-100 min, and the thickness of the deposited boron- or phosphorus-doped silicon nitride mask is 10-100 nm. The power of the infrared continuous laser is 50-200W, and the selective doping width is 1-40μm.

5. The method for preparing a heavily doped back contact battery according to claim 1, characterized in that, The method further includes, after the boron doping deposition and laser processing steps and between the secondary thin film deposition step: Cleaning and tunneling oxidation: RCA cleaning of silicon wafers and deposition of tunneling oxide film.

6. The method for preparing a heavily doped back contact battery according to claim 5, characterized in that, In the steps of cleaning and tunnel oxidation: RCA cleaning includes: first, cleaning the silicon wafer with a mixed HF / HNO3 solution, followed by a second cleaning with KOH. The ratio of HF, HNO3, and H2O in the HF / HNO3 solution is 1:3:5 to 1:5:

8. The temperature of the first cleaning is 10-60℃, and the time is 60-300s. The concentration of the KOH solution is 1-2.5wt%, and the reaction time of the second cleaning is 600-1200s, and the temperature is 65-85℃. The deposition of tunneling oxide films includes: high-density plasma chemical vapor deposition, in which oxygen and silane are used as process gases, the silane to oxygen flow ratio is 1:10 to 1:20, and the radio frequency power density is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 200℃-500℃, and the time is 1-10 min, resulting in a tunneling oxide film with a thickness of 1-2 nm.

7. The method for preparing a heavily doped back contact battery according to claim 1, characterized in that, In a single or double thin film deposition step, a polycrystalline silicon thin film or an amorphous silicon thin film is formed on the back side of a silicon wafer using one or more of high-density plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition or physical vapor deposition. The process gas uses a mixture of hydrogen, silane, and borane or phosphine, with a hydrogen to silane volume ratio of 0.1-500 and a hydrogen to borane or phosphine volume ratio of 0.1-500. The radio frequency power density is 0.5-20 mW / cm³. 2 The pressure is 0.2-50 mbar, the temperature is 30℃-500℃, the time is 10-100 min, and the thickness of the deposited film is 10-300 nm.

8. The method for preparing a heavily doped back contact battery according to claim 1, characterized in that, In the boron or phosphorus diffusion and patterning steps, the silicon wafer is annealed and crystallized in an annealing furnace. The annealing atmosphere is nitrogen or argon, with a flow rate of 2000-9000 sccm. The annealing temperature is 700-1080℃, and the time is 10-90 min. Patterning distinguishes between etched and non-etched areas. Patterning processes include one or more of screen printing, laser etching, and photolithography. In laser etching, the laser power is 200-1000W and the laser spot size is 30×30-300×300μm. In photolithography, a dry photoresist film is used as a mask and infrared light is used as the exposure light source.

9. The method for preparing a heavily doped back contact battery according to claim 1, characterized in that, Following the phosphorus doping deposition and laser processing steps, the method further includes: Surface treatment and electrode fabrication: acid etching, texturing, deposition of antireflective film, and grid line printing on silicon wafers.

10. A heavily doped back contact battery, characterized in that, It is prepared using the method for preparing heavily doped back contact cells according to any one of claims 1-9.

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