N-type topcon solar cell with anti-ultraviolet attenuation and preparation method thereof

Abstract

The application relates to the technical field of solar cells, in particular to an N-type TOPCon solar cell with anti-ultraviolet attenuation and a preparation method thereof. The front surface of the N-type TOPCon solar cell comprises an N-type silicon substrate, a boron diffusion emitter, a bottom aluminum oxide layer, an intermediate ultrathin silicon nitride layer, an intermediate ultrathin aluminum oxide layer and an outer silicon nitride layer arranged in sequence. When the conventional front surface only adopts the direct stacking of the aluminum oxide layer and the silicon nitride layer, the interface is more prone to charge disturbance, local defect accumulation and structure instability under ultraviolet irradiation. According to the application, the intermediate ultrathin silicon nitride layer and the intermediate ultrathin aluminum oxide layer are introduced, so that the ultraviolet stress originally concentrated on a single interface is dispersed into multiple nanoscale transition layers, thereby slowing down the interface instability process and inhibiting the attenuation of the passivation performance of the front surface.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, specifically to an N-type TOPCon solar cell with resistance to ultraviolet degradation and its fabrication method. Background Technology

[0002] N-type TOPCon solar cells have become one of the important technological routes for high-efficiency crystalline silicon solar cells due to their high photoelectric conversion efficiency and good industrialization foundation. In this type of solar cell, a boron-diffused emitter is typically placed on the front surface, upon which a composite passivation structure consisting of an aluminum oxide layer and a silicon nitride layer is formed to achieve functions such as interface passivation, field-effect passivation, and anti-reflection. Existing publicly available research indicates that the conventional structure of the front surface of TOPCon solar cells is typically Al₂O₃ / SiN. X The double-layer stack mainly provides good interface passivation and fixes negative charges, while the silicon nitride layer mainly plays the roles of protection, anti-reflection and hydrogen source storage.

[0003] However, with the large-scale application of TOPCon solar cells, their stability under ultraviolet irradiation conditions has gradually become apparent. Recent studies have shown that TOPCon solar cells and modules undergo significant ultraviolet-induced degradation under ultraviolet irradiation, and this degradation is related to the Al2O3 / SiN front surface. X The passivation stack is closely related. Related studies indicate that the UV decay process on the front surface is not caused by a single factor, but is coupled with factors such as charge trapping and release in the dielectric layer, hydrogen migration and accumulation in the passivation layer, and structural changes in the passivation stack.

[0004] Furthermore, existing technologies also demonstrate that conventional Al2O3 / SiN X In a bilayer structure, although hydrogen can participate in interface passivation during fabrication and subsequent heat treatment, it may also redistribute, migrate, or even induce new unstable states under ultraviolet stress. Simultaneously, the alumina layer significantly affects hydrogen transport. Existing studies have shown that increasing the thickness of the front surface alumina layer can improve the UV resistance of TOPCon solar cells to some extent, which indirectly indicates that there is still room for further optimization of existing conventional bilayer structures in terms of interface configuration, hydrogen transport pathways, and interlayer synergy.

[0005] However, most existing front surface passivation structures still primarily consist of a single aluminum oxide layer and a single silicon nitride layer directly stacked. This type of structure has a relatively simple interface transition and limited functional division between layers, making it difficult to finely control the passivation environment, hydrogen / deuterium distribution, and structural stability under ultraviolet irradiation in the near-interface region. Therefore, how to further improve the stability of the front surface passivation structure under ultraviolet irradiation while maintaining good passivation and optical performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the above problems, the present invention provides an N-type TOPCon solar cell with resistance to ultraviolet degradation, the front surface of which includes an N-type silicon substrate, a boron diffused emitter, a bottom alumina layer, an intermediate ultrathin silicon nitride layer, an intermediate ultrathin alumina layer, and an outer silicon nitride layer arranged in sequence.

[0007] This invention introduces an intermediate ultrathin silicon nitride layer and an intermediate ultrathin alumina layer between the conventional alumina layer and silicon nitride layer, reconstructing the original single alumina / silicon nitride abrupt interface into a multi-level transition interface. This optimizes the front surface passivation structure in terms of interface chemical environment, stress distribution, and migration path of hydrogen-related particles. The bottom alumina layer is close to the boron diffusion emitter and mainly serves to maintain good interface passivation and field-effect passivation. The intermediate ultrathin silicon nitride layer is located in the near-interface region and can act as a transition buffer layer to improve the interface matching between alumina and subsequent dielectric layers. The intermediate ultrathin alumina layer further restricts the disordered migration and escape of hydrogen-related particles. The outer silicon nitride layer provides external protection and stable coverage. As a result, charge disturbances, local defect accumulation, and structural instability that would otherwise easily concentrate at a single interface under ultraviolet irradiation are dispersed into multiple nanoscale transition layers. This not only slows down the formation and expansion of interface defects but also improves the overall stability of the front surface passivation structure, ultimately achieving effective suppression of ultraviolet attenuation.

[0008] Furthermore, the thickness of the bottom alumina layer is 2-12 nm, the thickness of the middle ultrathin silicon nitride layer is 0.5-2 nm, and the thickness of the outer silicon nitride layer is 40-100 nm. This thickness design allows the bottom alumina layer to form relatively stable interface passivation and field-effect passivation near the boron diffusion emitter, while the outer silicon nitride layer forms a continuous external protective layer and anti-reflection layer, thus ensuring the basic function of the front surface passivation structure. Simultaneously, both the middle ultrathin silicon nitride and alumina layers are set to nanometer-scale ultrathin thickness, allowing them to primarily function in the near-interface region between the bottom alumina layer and the outer silicon nitride layer, enabling fine-tuning of the interface structure without forming new main functional layers. Specifically, the middle ultrathin silicon nitride layer improves the interface transition between the bottom alumina layer and the subsequent dielectric layer, reducing interlayer abrupt changes and improving interface continuity; the middle ultrathin alumina layer, without significantly blocking interlayer synergy, restricts the propagation of disturbances and disordered particle migration in the near-interface region. Since the thickness of the intermediate ultrathin silicon nitride layer and the intermediate ultrathin alumina layer is relatively small, they can achieve interface buffering, stress dispersion and structural regulation at the nanoscale without significantly increasing the burden on the front surface dielectric layer. This is beneficial to further improve the stability of the front surface structure and its resistance to ultraviolet decay while maintaining the passivation and optical performance of the front surface.

[0009] Furthermore, the intermediate ultrathin silicon nitride layer is a deuterium-containing silicon nitride layer. This confines deuterium into the near-interface ultrathin region between the bottom alumina layer and the intermediate ultrathin alumina layer. This allows the intermediate ultrathin silicon nitride layer to function as both a local deuterium reservoir and a short-range deuterium donor layer near the critical interface, shortening the migration path of deuterium to regions susceptible to UV disturbances. Simultaneously, it avoids the excessive deuterium source from the overall deuterium-containing outer silicon nitride layer participating in long-range migration and disordered redistribution. Thus, deuterium primarily functions in the near-interface region where stabilization is most needed. Furthermore, compared to Si-H bonds, the Si-D bonds and / or ND bonds formed by deuterium... The bonds exhibit higher stability and are less prone to breakage and instability under ultraviolet irradiation. Therefore, they can more effectively suppress the migration of hydrogen-related particles, accumulation of interface defects, and charge disturbances induced by ultraviolet radiation. Combined with the clamping and confinement effect of the upper and lower alumina layers on the deuterium-containing ultrathin silicon nitride layer, the deuterium in the middle layer tends to participate in passivation in the short-range near-interface region rather than being ineffectively lost outward. Thus, without significantly changing the overall function of the outer main silicon nitride layer, the stability and anti-attenuation ability of the front surface passivation structure under ultraviolet irradiation are further improved.

[0010] Furthermore, the outer silicon nitride layer is a deuterium-containing silicon nitride layer. In this way, the middle ultrathin deuterium-containing silicon nitride layer can serve as a short-range deuterium supply layer near the critical interface, preferentially stabilizing the near-interface region most susceptible to ultraviolet disturbances, while the outer deuterium-containing silicon nitride layer can serve as a larger deuterium storage layer and protective layer, continuously replenishing deuterium during subsequent thermal processes or ultraviolet service, thus forming a dual-layer synergistic structure of precise passivation in the inner layer and slow-release replenishment in the outer layer.

[0011] Furthermore, the deuterium concentration in the intermediate ultrathin silicon nitride layer is higher than that in the outer silicon nitride layer. Preferentially placing the higher concentration of deuterium in the near-interface region closer to the bottom alumina layer and the boron diffused emitter allows deuterium to act more concentratedly on the critical passivation region most susceptible to UV irradiation, thereby shortening the migration path of deuterium to interface defect sites and improving local passivation efficiency. Simultaneously, controlling the deuterium concentration in the outer silicon nitride layer to be relatively low allows it to primarily serve as a deuterium storage and replenishment layer, as well as an external protection layer. This prevents excessive deuterium from causing large-scale disordered migration under UV or thermal stress, which could lead to new instabilities. The concentration gradient design creates a synergistic mechanism of efficient and stable near-interface passivation and slow-release replenishment at a low concentration in the outer layer, which is more conducive to suppressing the accumulation of interface defects, disordered migration of hydrogen-related particles, and passivation instability under UV irradiation, thereby further enhancing the UV degradation resistance of the front surface structure.

[0012] Furthermore, the density of the outer silicon nitride layer is greater than that of the middle ultrathin silicon nitride layer. Due to its relatively lower density, the middle ultrathin silicon nitride layer is better suited to accommodate and release beneficial hydrogen / deuterium-related particles in the near-interface region, making it more suitable as a transition layer and local supply layer near the underlying alumina layer. Conversely, the outer silicon nitride layer, with its higher density, is better suited to forming a continuous and stable external protective layer, reducing the intrusion of the external environment and inhibiting the ineffective diffusion and escape of hydrogen / deuterium-related particles to the outside. Thus, the two silicon nitride layers form a differentiated structure with a moderately active inner layer and a highly dense outer layer: the middle ultrathin silicon nitride layer focuses on improving the structural transition and local passivation in the near-interface region, while the outer silicon nitride layer focuses on maintaining overall film stability and limiting disordered migration under ultraviolet irradiation. This is more conducive to mitigating Si-H bond breakage, hydrogen-related particle redistribution, and interface defect accumulation caused by ultraviolet stress, thereby further enhancing the UV aging resistance of the front surface structure.

[0013] On the other hand, the present invention provides a method for fabricating an N-type TOPCon solar cell resistant to ultraviolet degradation, comprising the following steps: Step 1: Provide an N-type silicon substrate; Step 2: Perform boron diffusion on the front side of the N-type silicon substrate to form a boron-diffused emitter; Step 3: Form a bottom aluminum oxide layer on the surface of the boron diffused emitter; Step 4: Form an intermediate ultrathin silicon nitride layer on the bottom alumina layer; Step 5: Form an intermediate ultrathin aluminum oxide layer on the intermediate ultrathin silicon nitride layer; Step 6: Form an outer silicon nitride layer on the middle ultrathin alumina layer.

[0014] Furthermore, in step 4, one of the gases D2O, ND3, and D2 is introduced to pretreat the surface of the underlying alumina layer.

[0015] Furthermore, in step 5, an intermediate ultrathin silicon nitride layer is formed using plasma-enhanced atomic layer deposition, and deuterium-containing gas is introduced during the deposition process.

[0016] Furthermore, in step 5, the plasma-enhanced atomic layer deposition method employs a remote plasma approach. Remote plasma can generate plasma at a location far from the sample, ensuring that the surface reaching the intermediate ultrathin silicon nitride layer is primarily composed of highly reactive free radicals, while significantly reducing high-energy ion bombardment. This not only improves surface reactivity and film integrity at low temperatures but also reduces damage to the underlying alumina layer and near-interface region, avoiding surface defects, void formation, and film degradation caused by ion bombardment. Especially for the intermediate ultrathin silicon nitride layer in this invention, the remote plasma approach is more conducive to achieving uniform deposition while maintaining interface flatness and stability, thereby improving the structural quality of the multi-level transition interface and the UV fading resistance of the front surface passivation structure.

[0017] The beneficial effects of this invention are: (1) The present invention can improve the UV fading resistance of the front surface structure. When the traditional front surface is made up of only aluminum oxide layer and silicon nitride layer directly stacked, the interface is more prone to charge disturbance, local defect accumulation and structural instability under UV irradiation. However, the present invention introduces an intermediate ultrathin silicon nitride layer and an intermediate ultrathin aluminum oxide layer, so that the UV stress originally concentrated on a single interface is dispersed into multiple nanoscale transition layers, thereby slowing down the interface instability process and suppressing the decay of the passivation performance of the front surface.

[0018] (2) The present invention can improve the structural transition and interface matching in the near-interface region of the front surface. The bottom alumina layer and the outer silicon nitride layer have significant differences in material properties. When directly stacked, the interface abruptly is strong. However, the present invention, by setting an intermediate ultrathin silicon nitride layer and an intermediate ultrathin alumina layer, makes the interface transition from a single-level abrupt transition to a multi-level gradual transition, which is beneficial to improving the interlayer continuity, reducing local defects and stress concentration caused by interface mismatch, and improving the overall stability of the front surface stacked structure.

[0019] (3) This invention facilitates more precise control of hydrogen-related or deuterium-related particles in the near-interface region. The intermediate ultrathin silicon nitride layer is positioned close to the bottom alumina layer, which is more conducive to forming local storage and short-range supply in the key near-interface region; the intermediate ultrathin alumina layer can limit the disordered migration and escape of related particles. Thus, this invention enables beneficial particles to act more on the near-interface region that needs to be stabilized, rather than being randomly distributed in the entire outer medium, thereby improving local passivation efficiency and structural stability.

[0020] (4) The present invention can achieve structural optimization without significantly increasing the burden on the front surface. Both the intermediate ultrathin silicon nitride layer and the intermediate ultrathin alumina layer adopt a nanoscale ultrathin design, which enables them to play a fine control role in the near-interface region, rather than significantly changing the overall film thickness and the basic function of the front surface like the main functional layer. Therefore, it can further improve the UV resistance while maintaining the passivation performance and optical performance of the front surface.

[0021] (5) The preparation method of the present invention has good compatibility with the existing TOPCon solar cell front surface passivation process. The present invention mainly optimizes the hierarchical structure and functional division based on the existing alumina layer and silicon nitride layer deposition, without changing the basic process logic of N-type silicon substrate preparation, boron diffusion to form the emitter and front surface dielectric layer deposition. Therefore, it is easy to implement in combination with existing equipment and process flow, which helps to reduce the difficulty of process introduction and the threshold for industrial application.

[0022] Based on the above beneficial effects, this invention has good application prospects in the field of solar cell technology. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an N-type TOPCon solar cell that is resistant to ultraviolet degradation.

[0024] Figure 2 This is a schematic diagram of a method for fabricating an N-type TOPCon solar cell that resists ultraviolet degradation.

[0025] In the figure: 1. N-type silicon substrate; 2. Boron diffused emitter; 3. Bottom alumina layer; 4. Middle ultrathin silicon nitride layer; 5. Middle ultrathin alumina layer; 6. Outer silicon nitride layer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Example 1

[0027] This embodiment provides an N-type TOPCon solar cell resistant to ultraviolet degradation, such as... Figure 1 As shown, its front surface includes an N-type silicon substrate 1, a boron diffused emitter 2, a bottom aluminum oxide layer 3, an intermediate ultrathin silicon nitride layer 4, an intermediate ultrathin aluminum oxide layer 5, and an outer silicon nitride layer 6 arranged in sequence.

[0028] In this battery, the N-type silicon substrate 1 serves as the main substrate. A boron-diffused emitter 2 is disposed on the front surface of the N-type silicon substrate 1, forming the emitter structure on the front surface of the battery. A bottom alumina layer 3 is disposed on the surface of the boron-diffused emitter 2, close to the boron-diffused emitter 2, forming the basic passivation layer on the front surface.

[0029] An intermediate ultrathin silicon nitride layer 4 is disposed on the side of the bottom alumina layer 3 away from the boron diffusion emitter 2. The intermediate ultrathin silicon nitride layer 4 is a nanoscale ultrathin structure, located in the middle of the front surface stack structure, and serves to form a transition interface between the bottom alumina layer 3 and the subsequent dielectric layer. An intermediate ultrathin alumina layer 5 is disposed on the side of the intermediate ultrathin silicon nitride layer 4 away from the bottom alumina layer 3. The intermediate ultrathin alumina layer 5 is also a nanoscale ultrathin structure. The intermediate ultrathin silicon nitride layer 4 and the intermediate ultrathin alumina layer 5 are jointly disposed between the bottom alumina layer 3 and the outer silicon nitride layer 6, used to reconstruct the original single interlayer interface on the front surface into a multi-level transition interface.

[0030] The outer silicon nitride layer 6 is disposed on the side of the intermediate ultrathin alumina layer 5 away from the intermediate ultrathin silicon nitride layer 4, and is located on the outermost side of the front surface structure. The outer silicon nitride layer 6 is used to form the outer cover layer of the front surface.

[0031] In this embodiment, the thickness of the bottom alumina layer 3 is 2-12 nanometers, the thickness of the middle ultrathin silicon nitride layer 4 is 0.5-2 nanometers, the thickness of the middle ultrathin alumina layer 5 is 0.5-2 nanometers, and the thickness of the outer silicon nitride layer 6 is 40-100 nanometers. Thus, the bottom alumina layer 3 and the outer silicon nitride layer 6 constitute the main functional layers in the front surface stack structure, while the middle ultrathin silicon nitride layer 4 and the middle ultrathin alumina layer 5, due to their smaller thickness, are mainly used to regulate the near-interface region between the bottom alumina layer 3 and the outer silicon nitride layer 6.

[0032] In this embodiment, a TOPCon passivation contact structure is provided on the back side of the N-type TOPCon solar cell. Specifically, a tunneling oxide layer, a doped polycrystalline silicon layer, a back passivation layer, and a back metal electrode are sequentially disposed on the back side of the N-type silicon substrate 1. The tunneling oxide layer is disposed close to the N-type silicon substrate 1, the doped polycrystalline silicon layer is disposed on the side of the tunneling oxide layer away from the N-type silicon substrate 1, and the back passivation layer is disposed on the side of the doped polycrystalline silicon layer away from the tunneling oxide layer. The back metal electrode is electrically connected to the back passivation contact structure. The front surface and the back surface together constitute a complete N-type TOPCon solar cell structure.

[0033] In this embodiment, by setting an intermediate ultrathin silicon nitride layer 4 and an intermediate ultrathin aluminum oxide layer 5 between the bottom aluminum oxide layer 3 and the outer silicon nitride layer 6, a multi-level transition stacked structure is formed on the front surface, which is different from the conventional two-layer structure that only includes an aluminum oxide layer and a silicon nitride layer. Example 2

[0034] Based on Example 1, the intermediate ultrathin silicon nitride layer 4 is a deuterium-containing silicon nitride layer, and only the intermediate ultrathin silicon nitride layer 4 contains deuterium, while the bottom alumina layer 3, the intermediate ultrathin alumina layer 5 and the outer silicon nitride layer 6 do not introduce deuterium.

[0035] Specifically, in the intermediate ultrathin silicon nitride layer 4, deuterium exists in a bonded state within the silicon nitride network, forming Si-D bonds and / or ND bonds. The deuterium concentration in the intermediate ultrathin silicon nitride layer 4 is 5 × 10⁻⁶. 20 atoms / cm 3 ~1×10 22 atoms / cm 3 In some embodiments, deuterium atoms in the intermediate ultrathin silicon nitride layer 4 account for 0.5 at% to 20 at% of the total number of atoms in the intermediate ultrathin silicon nitride layer 4.

[0036] In this embodiment, the thickness of the intermediate ultrathin silicon nitride layer 4 is preferably 0.8 nm to 1.5 nm, for example, it can be 1.0 nm, 1.2 nm, or 1.5 nm. When the thickness of the intermediate ultrathin silicon nitride layer 4 is 1.0 nm, its deuterium concentration is controlled to be 1 × 10⁻⁶. 21 atoms / cm 3 ~3×10 21 atoms / cm 3 When the thickness of the intermediate ultrathin silicon nitride layer 4 is 1.2 nm to 1.5 nm, its deuterium concentration is controlled to be 2 × 10⁻⁶. 21 atoms / cm 3 ~8×10 21 atoms / cm 3 This ensures that the intermediate ultrathin silicon nitride layer 4 maintains the characteristics of an ultrathin transition layer while having a good local deuterium storage capacity.

[0037] Furthermore, the deuterium in the intermediate ultrathin silicon nitride layer 4 can be uniformly distributed along its thickness direction; or, the deuterium in the intermediate ultrathin silicon nitride layer 4 can be distributed in a gradient from the side near the bottom alumina layer 3 to the side near the intermediate ultrathin alumina layer 5. Preferably, the deuterium concentration in the intermediate ultrathin silicon nitride layer 4 near the bottom alumina layer 3 is higher than the deuterium concentration near the intermediate ultrathin alumina layer 5. For example, the local deuterium concentration near the bottom alumina layer 3 is 3 × 10⁻⁶. 21 atoms / cm 3 ~1×10 22 atoms / cm3 The local deuterium concentration near the middle ultrathin alumina layer 5 is 5 × 10⁻⁶. 20 atoms / cm 3 ~3×10 21 atoms / cm 3 This results in deuterium being more concentrated in the region near the critical interface.

[0038] In this embodiment, since only the intermediate ultrathin silicon nitride layer 4 contains deuterium, the deuterium is confined within the ultrathin region between the bottom alumina layer 3 and the intermediate ultrathin alumina layer 5, making the intermediate ultrathin silicon nitride layer 4 serve simultaneously as a near-interface transition layer and a local deuterium reservoir layer. This allows deuterium to be distributed closer to the key passivation region of the front surface, shortening the migration path of deuterium to near-interface defect sites and reducing the long-range migration and disordered redistribution that may result from the overall deuterium content of the outer main silicon nitride layer, thus improving the stability of the front surface structure under ultraviolet irradiation conditions. Example 3

[0039] Based on Example 2, the outer silicon nitride layer 6 is also a deuterium-containing silicon nitride layer, and the deuterium concentration in the middle ultrathin silicon nitride layer 4 is higher than the deuterium concentration in the outer silicon nitride layer 6, thereby forming a layered deuterium-containing structure on the front surface consisting of a high-concentration deuterium-containing layer near the interface and a low-concentration deuterium-containing layer on the outside.

[0040] Specifically, in the intermediate ultrathin silicon nitride layer 4, deuterium exists in a bonded state within the silicon nitride network, forming Si-D bonds and / or ND bonds; similarly, in the outer silicon nitride layer 6, deuterium exists in a bonded state within the silicon nitride network, forming Si-D bonds and / or ND bonds. The deuterium concentration in the intermediate ultrathin silicon nitride layer 4 is 2 × 10⁻⁶. 21 atoms / cm 3 ~1×10 22 atoms / cm 3 The deuterium concentration in the outer silicon nitride layer 6 is 5 × 10⁶. 19 atoms / cm 3 ~2×10 21 atoms / cm 3 .

[0041] In some embodiments, deuterium atoms account for 1 at% to 15 at% of the total number of atoms in the intermediate ultrathin silicon nitride layer 4; and deuterium atoms account for 0.05 at% to 2 at% of the total number of atoms in the outer silicon nitride layer 6. For example, when the thickness of the intermediate ultrathin silicon nitride layer 4 is 1.0 nanometers, its deuterium concentration is 5 × 10⁻⁶. 21 atoms / cm 3 Approximately; when the thickness of the outer silicon nitride layer 6 is 75 nanometers, its deuterium concentration is 5 × 10⁻⁶. 20 atoms / cm 3Approximately. For example, the deuterium concentration in the intermediate ultrathin silicon nitride layer 4 is 8 × 10⁻⁶. 21 atoms / cm 3 The deuterium concentration in the outer silicon nitride layer 6 is 8 × 10⁶. 20 atoms / cm 3 Alternatively, the deuterium concentration in the intermediate ultrathin silicon nitride layer 4 is 3 × 10⁻⁶. 21 atoms / cm 3 The deuterium concentration in the outer silicon nitride layer 6 is 3 × 10⁶. 20 atoms / cm 3 .

[0042] Furthermore, the deuterium in the outer silicon nitride layer 6 can be uniformly distributed along its thickness direction; or, the deuterium in the outer silicon nitride layer 6 can decrease from the side near the intermediate ultrathin alumina layer 5 to the side away from the intermediate ultrathin alumina layer 5. Preferably, the deuterium concentration on the side of the outer silicon nitride layer 6 near the intermediate ultrathin alumina layer 5 is higher than the deuterium concentration on its outer surface side. For example, the local deuterium concentration on the side of the outer silicon nitride layer 6 near the intermediate ultrathin alumina layer 5 can be 5 × 10⁻⁶. 20 atoms / cm 3 ~2×10 21 atoms / cm 3 The local deuterium concentration near the outer surface is 1×10⁻⁶. 19 atoms / cm 3 ~5×10 20 atoms / cm 3 This results in the outer silicon nitride layer 6 forming a relatively low-concentration slow-release deuterium storage region.

[0043] In this embodiment, the intermediate ultrathin silicon nitride layer 4 serves as a high-concentration deuterium-containing layer near the interface, close to the bottom alumina layer 3 and the boron diffused emitter 2. This allows deuterium to concentrate more near the key passivation region, thereby shortening the migration path of deuterium to the near-interface region susceptible to ultraviolet irradiation and improving local stabilization capability. The outer silicon nitride layer 6, as a thicker low-concentration deuterium-containing layer, functions as a deuterium storage layer and a slow-release replenishment layer while maintaining external protection and anti-reflection functions. Since the deuterium concentration in the intermediate ultrathin silicon nitride layer 4 is higher than that in the outer silicon nitride layer 6, a gradient deuterium-containing structure is formed on the front surface, characterized by high-concentration stable passivation near the interface and low-concentration slow-release replenishment in the outer layer. This reduces the large-scale disordered migration of excess deuterium sources in the outer layer under thermal or ultraviolet stress, while ensuring a high degree of deuterium enrichment in the key near-interface region, thereby further improving the stability and anti-ultraviolet decay capability of the front surface passivation structure. Example 4

[0044] Based on Example 3, the density of the outer silicon nitride layer 6 is greater than that of the middle ultrathin silicon nitride layer 4.

[0045] Specifically, the intermediate ultrathin silicon nitride layer 4 is a relatively low-density silicon nitride layer, and the outer silicon nitride layer 6 is a relatively high-density silicon nitride layer. The thickness of the intermediate ultrathin silicon nitride layer 4 is 0.8 nm to 1.5 nm, for example, 1.0 nm or 1.2 nm; the thickness of the outer silicon nitride layer 6 is 70 nm to 85 nm, for example, 75 nm or 80 nm.

[0046] In some embodiments, the density of the silicon nitride layer can be comprehensively characterized by parameters such as film density, refractive index, wet etching rate, and hydrogen content. Preferably, the film density of the intermediate ultrathin silicon nitride layer 4 is 2.2 g / cm³. 3 ~2.5g / cm 3 The film density of the outer silicon nitride layer 6 is 2.7 g / cm³. 3 ~3.0g / cm 3 .

[0047] In this embodiment, the intermediate ultrathin silicon nitride layer 4, due to its relatively low density, is more conducive to serving as a transition layer between the bottom alumina layer 3 and the intermediate ultrathin alumina layer 5, forming a relatively smooth structural transition in the near-interface region while retaining a certain degree of local activity and buffering capacity. The outer silicon nitride layer 6, due to its relatively high density, is more conducive to forming a continuous and stable external capping layer, thereby enhancing the overall stability, barrier capacity, and external protection capability of the front surface stacked structure. Thus, the intermediate ultrathin silicon nitride layer 4 and the outer silicon nitride layer 6 form a layered structure of "relatively loose transition in the inner layer and highly dense protection in the outer layer," which is beneficial for improving interlayer matching in the near-interface region while suppressing the influence of the external environment and the disordered escape of related particles. Example 5

[0048] This embodiment provides a method for fabricating an N-type TOPCon solar cell resistant to ultraviolet degradation, such as... Figure 2 As shown, it includes 6 steps.

[0049] Step 1: Provide the N-type silicon substrate 1.

[0050] An N-type monocrystalline silicon wafer is provided as the N-type silicon substrate 1. The N-type silicon substrate 1 can be a phosphorus-doped monocrystalline silicon wafer with a resistivity of 1–5 Ω·cm and a thickness of 100–180 μm, for example, 120 μm, 140 μm, or 160 μm. Preferably, before subsequent processes, the N-type silicon substrate 1 is first texturized and cleaned to remove organic contaminants, metallic impurities, and the natural oxide layer from its surface, and to form a textured surface structure on its surface to facilitate the subsequent formation of the front surface structure and improve the utilization of incident light. After cleaning, the front side of the N-type silicon substrate 1 serves as the light-receiving surface.

[0051] Step 2: Boron diffusion is performed on the front side of the N-type silicon substrate 1 to form a boron-diffused emitter 2.

[0052] Boron diffusion is performed on the front side of the N-type silicon substrate 1 to form a boron-diffused emitter 2. Boron diffusion can be performed using boron source diffusion methods commonly used in the art. After boron diffusion, the silicon wafer is post-cleaned to remove the borosilicate glass layer and residual contaminants formed on the surface during diffusion, resulting in a clean emitter structure. If necessary, the edge areas can also be isolated to prevent short circuits between the front and back sides.

[0053] Step 3: Form a bottom aluminum oxide layer 3 on the surface of the boron diffused emitter 2.

[0054] A bottom alumina layer 3 is formed on the surface of the boron-diffused emitter 2. The bottom alumina layer 3 can be formed using atomic layer deposition, preferably with trimethylaluminum as the aluminum source and water vapor as the oxygen source. Alternating pulses are used to supply the aluminum and oxygen sources, followed by purging, to form a continuous and uniform alumina thin layer on the surface of the boron-diffused emitter 2. The thickness of the bottom alumina layer 3 is 2–12 nm. The bottom alumina layer 3 is positioned close to the boron-diffused emitter 2 to provide basic interface passivation and field-effect passivation of the front surface.

[0055] Step 4: Form an intermediate ultrathin silicon nitride layer 4 on the bottom alumina layer 3.

[0056] An intermediate ultrathin silicon nitride layer 4 is formed on the side of the bottom alumina layer 3 away from the boron diffusion emitter 2. The intermediate ultrathin silicon nitride layer 4 can be formed using plasma-enhanced atomic layer deposition (PEALD). Preferably, a silicon-containing precursor and a nitrogen-containing reactive gas are alternately applied to the surface of the bottom alumina layer 3, and the surface reactivity is enhanced by plasma to form a nanoscale ultrathin silicon nitride layer. The thickness of the intermediate ultrathin silicon nitride layer 4 is 0.5–2 nm, preferably 0.8–1.5 nm. Due to its relatively small thickness, the intermediate ultrathin silicon nitride layer 4 mainly serves as a transition layer between the bottom alumina layer 3 and the subsequent dielectric layer, improving interlayer interface transition, mitigating interface abrupt changes, and regulating the structural state of the near-interface region.

[0057] Step 5: Form an intermediate ultrathin aluminum oxide layer 5 on the intermediate ultrathin silicon nitride layer 4.

[0058] An intermediate ultrathin alumina layer 5 is formed on the side of the intermediate ultrathin silicon nitride layer 4 away from the underlying alumina layer 3. The intermediate ultrathin alumina layer 5 can be formed using atomic layer deposition, preferably with alternating pulse deposition using trimethylaluminum and water vapor as reaction precursors. The thickness of the intermediate ultrathin alumina layer 5 is 0.5–2 nm, preferably 0.8–1.5 nm. The intermediate ultrathin alumina layer 5, together with the underlying alumina layer 3 and the intermediate ultrathin silicon nitride layer 4, constitutes a multi-level transition interface structure on the front surface, which further improves interface continuity and restricts disturbance propagation and disordered particle migration in the near-interface region.

[0059] Step 6: Form an outer silicon nitride layer 6 on the middle ultrathin alumina layer 5.

[0060] An outer silicon nitride layer 6 is formed on the side of the intermediate ultrathin alumina layer 5 away from the intermediate ultrathin silicon nitride layer 4. The outer silicon nitride layer 6 can be formed using plasma-enhanced chemical vapor deposition (PECVD). By introducing silicon and nitrogen source gases into the reaction space, a continuous silicon nitride layer is deposited under plasma conditions. The thickness of the outer silicon nitride layer 6 is 40–100 nm, preferably 70–85 nm. The outer silicon nitride layer 6 is located on the outermost side of the front surface structure and primarily serves to form an external protective layer and antireflective layer. Together with the bottom alumina layer 3, the intermediate ultrathin silicon nitride layer 4, and the intermediate ultrathin alumina layer 5, it constitutes a multilayer composite passivation structure on the front surface.

[0061] Through the above steps, a multi-level transition front surface structure is formed on the front surface of the N-type silicon substrate 1, consisting of the bottom alumina layer 3, the middle ultrathin silicon nitride layer 4, the middle ultrathin alumina layer 5, and the outer silicon nitride layer 6.

[0062] After completing step 6 above, a TOPCon passivation contact structure is fabricated on the back side of the N-type silicon substrate 1. Specifically, a tunneling oxide layer is formed on the back side of the N-type silicon substrate 1, and a doped polycrystalline silicon layer is formed on the tunneling oxide layer, followed by the formation of a back passivation layer and a back metal electrode. The tunneling oxide layer can be an ultrathin silicon oxide layer, the doped polycrystalline silicon layer can be a phosphorus-doped polycrystalline silicon layer, and the back passivation layer can be an aluminum oxide layer, a silicon nitride layer, or a composite layer of both, thereby forming a complete N-type TOPCon solar cell together with the front surface structure. Example 6

[0063] Based on Example 5, in step 4, before forming the intermediate ultrathin silicon nitride layer 4, one of the gases D2O, ND3, and D2 is introduced to pretreat the surface of the bottom alumina layer 3 to change the surface structure of the bottom alumina layer 3.

[0064] Specifically, after the formation of the bottom alumina layer 3 in step 3, the intermediate ultrathin silicon nitride layer 4 is not deposited immediately. Instead, the bottom alumina layer 3 is first exposed to a pretreatment atmosphere. The pretreatment gas can be any one of D2O, ND3, and D2. In some embodiments, the pretreatment gas is preferably introduced in a pulsed manner to ensure that the pretreatment gas makes full contact with the surface of the bottom alumina layer 3 before the residual gas in the reaction chamber is discharged to avoid interfering with the subsequent formation of the intermediate ultrathin silicon nitride layer 4.

[0065] When D2O is used as the pretreatment gas, the hydroxyl structures on the surface of the bottom alumina layer 3 undergo deuteration, thereby forming a surface termination structure containing -OD groups on its surface. This results in an interface state on the surface of the bottom alumina layer 3 that is more conducive to the formation of the subsequent nitrogen-containing dielectric layer. In some embodiments, the D2O introduction time is 3 to 20 seconds, and the number of introductions is 1 to 20 times.

[0066] When ND3 is used as the pretreatment gas, a deuterium-containing nitrogen-containing termination structure is formed on the surface of the bottom alumina layer 3, and a -ND3-containing structure is formed on the surface of the bottom alumina layer 3. X The surface state of the groups improves the interfacial transition between the intermediate ultrathin silicon nitride layer 4 and the underlying alumina layer 3. In some embodiments, ND 3 It can be introduced by pulse induction, with a single induction time of 2 to 10 seconds and the number of inductions ranging from 1 to 15.

[0067] When D2 is used as the pretreatment gas, it is used to deuterate the surface of the underlying alumina layer 3 to adjust its surface activity state and surface termination structure. In some embodiments, D2 can be introduced alone; in other embodiments, D2 can also be used in conjunction with a plasma environment for surface pretreatment to improve the surface treatment effect. The introduction time of D2 can be 5 seconds to 30 seconds.

[0068] The pretreatment step is performed under low-damage conditions to avoid disrupting the original continuity and flatness of the underlying alumina layer 3. After pretreatment, a modified surface termination structure is formed on the surface of the underlying alumina layer 3, upon which an intermediate ultrathin silicon nitride layer 4 is then formed. This results in a more favorable bonding state between the intermediate ultrathin silicon nitride layer 4 and the underlying alumina layer 3, and facilitates the subsequent introduction of deuterium into the intermediate ultrathin silicon nitride layer 4 or improves the distribution stability of deuterium in the near-interface region. Example 7

[0069] Based on Example 6, in step 5, the intermediate ultrathin silicon nitride layer 4 is formed by plasma-enhanced atomic layer deposition, and deuterium-containing gas is introduced during the deposition process to introduce deuterium into the intermediate ultrathin silicon nitride layer 4, thereby making the intermediate ultrathin silicon nitride layer 4 a deuterium-containing silicon nitride layer.

[0070] Specifically, after pretreatment of the surface of the bottom alumina layer 3, an intermediate ultrathin silicon nitride layer 4 is formed on the surface of the bottom alumina layer 3 using plasma-enhanced atomic layer deposition (PEALD). The PALD method employs alternating pulse supply of silicon source precursor and reactive gas. In each deposition cycle, the silicon source precursor is first introduced into the reaction chamber, causing it to adsorb onto the surface of the bottom alumina layer 3. Subsequently, nitrogen-containing reactive gas and deuterium-containing gas are introduced, and under the action of plasma, the silicon source precursor and reactive gas undergo a surface reaction, thereby forming the intermediate ultrathin silicon nitride layer 4 layer by layer.

[0071] The deuterium-containing gas is one of D2, ND3, a mixture of N2 and D2, or a mixture of N2 and ND3. Preferably, the deuterium-containing gas and the nitrogen-containing reactive gas participate together in the plasma-enhanced atomic layer deposition process, so that deuterium is simultaneously incorporated into the silicon nitride network during the formation of the intermediate ultrathin silicon nitride layer 4. Thus, the deuterium in the intermediate ultrathin silicon nitride layer 4 preferably exists in the form of Si-D bonds and / or ND bonds.

[0072] In some embodiments, when D2 is used as the deuterium-containing gas, D2 and N2 can be introduced together into the plasma region to form deuterium-containing active species in the plasma and introduce them into the intermediate ultrathin silicon nitride layer 4 during the deposition process. In this case, the flow rate of D2 is 20 sccm to 200 sccm.

[0073] In other embodiments, when ND3 is used as the deuterium-containing gas, ND3 can serve as both a nitrogen-containing gas source and a deuterium-containing gas source, thereby achieving deuterium introduction while forming the intermediate ultrathin silicon nitride layer 4. In this case, the flow rate of ND3 is 20 sccm to 150 sccm.

[0074] In some other embodiments, a mixture of N2 and D2 or a mixture of N2 and ND3 can be used to further adjust the ratio of nitrogen to deuterium, thereby controlling the deuterium content in the intermediate ultrathin silicon nitride layer 4.

[0075] Preferably, during plasma-enhanced atomic layer deposition, deuterium-containing gas is introduced in a pulsed manner. The duration of a single deuterium-containing gas pulse is 1 to 10 seconds; the duration of a single plasma exposure is 2 to 15 seconds; and the number of deposition cycles can be set according to the target thickness of the intermediate ultrathin silicon nitride layer 4, for example, 10 to 40 times. By controlling the number of deposition cycles, the thickness of the intermediate ultrathin silicon nitride layer 4 is controlled to be between 0.8 nanometers and 1.5 nanometers.

[0076] Deuterium can be uniformly distributed in the intermediate ultrathin silicon nitride layer 4; or, deuterium can be distributed in a gradient from the side near the bottom alumina layer 3 to the side near the intermediate ultrathin alumina layer 5. Preferably, the deuterium concentration on the side near the bottom alumina layer 3 is higher than the deuterium concentration on the side away from the bottom alumina layer 3.

[0077] Furthermore, in this embodiment, since deuterium-containing gas is simultaneously introduced during the formation of the intermediate ultrathin silicon nitride layer 4, deuterium can be directly incorporated into its network structure during the growth stage of the intermediate ultrathin silicon nitride layer 4, rather than being subsequently introduced from the outside after the film layer is formed. This allows for a more uniform and stable distribution of deuterium within the intermediate ultrathin silicon nitride layer 4, and enables the intermediate ultrathin silicon nitride layer 4 to form a near-interface deuterium-containing layer located between the bottom alumina layer 3 and the intermediate ultrathin alumina layer 5, thereby improving the stability of the near-interface region of the front surface.

[0078] In a specific example, the surface of the bottom alumina layer 3 is first pretreated with D2O, and then an intermediate ultrathin silicon nitride layer 4 is formed by plasma-enhanced atomic layer deposition. During the deposition process, silicon source precursor, N2 and D2 are introduced, with a D2 flow rate of 50 sccm, an N2 flow rate of 100 sccm, a single D2 pulse duration of 5 seconds, a single plasma exposure time of 8 seconds, and 20 cycles, to obtain a deuterium-containing intermediate ultrathin silicon nitride layer 4 with a thickness of about 1.0 nanometers.

[0079] In another specific example, the surface of the bottom alumina layer 3 was first pretreated with ND3, and then an intermediate ultrathin silicon nitride layer 4 was formed by plasma-enhanced atomic layer deposition. During the deposition process, a silicon source precursor and ND3 were introduced, with an ND3 flow rate of 60 sccm, a single pulse time of 4 seconds, a single plasma exposure time of 10 seconds, and 25 cycles, to obtain a deuterium-containing intermediate ultrathin silicon nitride layer 4 with a thickness of about 1.2 nanometers. Example 8

[0080] Based on Example 7, in step 5, the plasma-enhanced atomic layer deposition method employs a remote plasma method to form the intermediate ultrathin silicon nitride layer 4.

[0081] Specifically, during the formation of the intermediate ultrathin silicon nitride layer 4, deuterium-containing gas and nitrogen-containing gas first enter the plasma excitation region at a location far from the N-type silicon substrate 1. Under the action of the remote plasma, deuterium-containing active species and nitrogen-containing active species are generated. Subsequently, the deuterium-containing active species and nitrogen-containing active species are transported to the surface of the bottom alumina layer 3 and react with the silicon source precursor adsorbed on the surface, thereby forming the intermediate ultrathin silicon nitride layer 4 layer by layer. The remote plasma excitation region is separated from the region where the N-type silicon substrate 1 is located, so that the surface of the bottom alumina layer 3 is mainly in contact with the active free radicals transported remotely, rather than being directly in the high-energy plasma bombardment region.

[0082] In some embodiments, in the remote plasma method, the sample placement area and the plasma generation area are arranged sequentially along the gas flow direction, and the N-type silicon substrate 1 is located in the downstream reaction area. The deuterium-containing gas can be one of D2, ND3, a mixture of N2 and D2, or a mixture of N2 and ND3, and the nitrogen-containing gas can be N2, NH3, or ND3. In the remote plasma method, the plasma power is 100W to 500W; the single plasma exposure time is 2 seconds to 15 seconds; and the temperature of the N-type silicon substrate 1 is 200℃ to 400℃.

[0083] Furthermore, in this embodiment, by employing a remote plasma method, it is possible to ensure that both deuterium-containing and nitrogen-containing reactive species possess high reactivity while reducing the direct bombardment of high-energy ions on the surface and near-interface region of the underlying alumina layer 3. This reduces the risk of damage to the continuity, surface smoothness, and interface structure of the underlying alumina layer 3. This is more conducive to forming a continuous, uniform, and controllable thickness intermediate ultrathin silicon nitride layer 4 on the surface of the underlying alumina layer 3, and also facilitates the stable incorporation of deuterium into the intermediate ultrathin silicon nitride layer 4.

[0084] In summary, this invention addresses the problems of passivation degradation, interfacial instability, and disordered migration of hydrogen-related particles in the conventional alumina / silicon nitride bilayer structure of the front surface of existing N-type TOPCon solar cells under ultraviolet irradiation. It proposes a front surface passivation structure with multi-level transition interfaces and its preparation method. This scheme further incorporates an intermediate ultrathin silicon nitride layer 4 and an intermediate ultrathin alumina layer 5 between the bottom alumina layer 3 and the outer silicon nitride layer 6, reconstructing the originally single interlayer interface into a multi-level nano-transition interface. This improves interlayer matching, disperses local stress, regulates the structural state near the interface region, and enhances the stability of the front surface structure under ultraviolet irradiation. Furthermore, by introducing deuterium into the intermediate ultrathin silicon nitride layer 4, or by introducing deuterium in layers between the intermediate ultrathin silicon nitride layer 4 and the outer silicon nitride layer 6, the higher stability of Si-D bonds and / or ND bonds compared to Si-H bonds and / or NH bonds can further suppress the accumulation of interface defects and passivation instability induced by ultraviolet radiation. At the same time, the structural design of this invention is based on the existing TOPCon front surface dielectric layer process. The overall process route is clear, and it has good compatibility with existing equipment and production lines. It is easy to implement and facilitates engineering implementation and industrial application. Therefore, it not only has clear technical improvement significance, but also has high practical value and promotion value.

[0085] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An N-type TOPCon solar cell resistant to ultraviolet degradation, characterized in that: Its front surface includes an N-type silicon substrate, a boron diffused emitter, a bottom alumina layer, an intermediate ultrathin silicon nitride layer, an intermediate ultrathin alumina layer, and an outer silicon nitride layer arranged in sequence.

2. The N-type TOPCon solar cell with UV degradation resistance as described in claim 1, characterized in that: The thickness of the bottom alumina layer is 2-12 nanometers, the thickness of the middle ultrathin silicon nitride layer is 0.5-2 nanometers, and the thickness of the outer silicon nitride layer is 40-100 nanometers.

3. The N-type TOPCon solar cell with UV degradation resistance as described in claim 1, characterized in that: The intermediate ultrathin silicon nitride layer is a deuterium-containing silicon nitride layer.

4. The N-type TOPCon solar cell with UV degradation resistance as described in claim 3, characterized in that: The outer silicon nitride layer is a deuterium-containing silicon nitride layer.

5. The N-type TOPCon solar cell with UV degradation resistance as described in claim 4, characterized in that: The deuterium concentration in the middle ultrathin silicon nitride layer is higher than that in the outer silicon nitride layer.

6. The N-type TOPCon solar cell with UV degradation resistance as described in claim 1, characterized in that: The density of the outer silicon nitride layer is greater than that of the middle ultrathin silicon nitride layer.

7. The method for preparing an N-type TOPCon solar cell with UV degradation resistance as described in claim 1, characterized in that, Includes the following steps: Step 1: Provide the N-type silicon substrate; Step 2: Perform boron diffusion on the front side of the N-type silicon substrate to form the boron-diffused emitter; Step 3: Form the underlying aluminum oxide layer on the surface of the boron diffusion emitter; Step 4: Form the intermediate ultrathin silicon nitride layer on the bottom alumina layer; Step 5: Form the intermediate ultrathin alumina layer on the intermediate ultrathin silicon nitride layer; Step 6: Form the outer silicon nitride layer on the intermediate ultrathin alumina layer.

8. The method for preparing an N-type TOPCon solar cell resistant to ultraviolet degradation as described in claim 7, characterized in that: In step 4, one of the gases D2O, ND3, and D2 is introduced to pretreat the surface of the underlying alumina layer.

9. The method for preparing an N-type TOPCon solar cell resistant to ultraviolet degradation as described in claim 8, characterized in that: In step 5, the intermediate ultrathin silicon nitride layer is formed using plasma-enhanced atomic layer deposition (PEALD), and deuterium-containing gas is introduced during the deposition process.

10. The method for preparing an N-type TOPCon solar cell with UV degradation resistance as described in claim 9, characterized in that: In step 5, the plasma-enhanced atomic layer deposition method employs a remote plasma approach.

Images