Tunnel oxide passivated back contact cells and methods of making same

Abstract

The present disclosure relates to the technical field of solar cells, and discloses a tunnel oxide passivated back contact cell and a preparation method thereof. The tunnel oxide passivated back contact cell comprises a substrate layer, a passivation contact layer, a first doped semiconductor structure, a second doped semiconductor structure, a first electrode and a second electrode. The substrate layer comprises a light-receiving surface and a back surface arranged oppositely. The passivation contact layer is formed on the light-receiving surface side, and the surface of the passivation contact layer is shaped as a first textured structure with a plurality of first micro-units. In the direction from the light-receiving surface to the back surface, the cross-sectional size of the first micro-units gradually increases, and the doping concentration of the first micro-units gradually decreases. The first doped semiconductor structure and the second doped semiconductor structure are alternately formed on the back surface side. The first electrode and the second electrode are respectively arranged on the first doped semiconductor structure and the second doped semiconductor structure. In the present disclosure, the doping concentration of the first micro-units gradually decreases, thereby protecting the cell from ultraviolet-induced degradation.

Description

Technical Field

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

[0002] Ultraviolet-induced degradation is one of the key factors affecting the long-term stability of crystalline silicon solar cells outdoors. Studies have shown that ultraviolet-induced degradation is mainly caused by the increase in the density of silicon dangling bond defect states in the silicon nitride antireflection layer on the front side of the cell under long-term ultraviolet light irradiation, as well as the migration and accumulation of fixed charges, which leads to a significant increase in the recombination rate at the passivation interface on the front side, and thus causes a simultaneous decrease in open-circuit voltage and short-circuit current.

[0003] To mitigate UV-induced degradation, related technologies focus on optimizing the design of the battery's backside structure. For example, the traditional pyramidal textured surface of the backside isolation region is replaced with a polished surface. This enhances the internal reflection effect on the backside, increasing the short-circuit current. Furthermore, masking techniques are used to control the height difference between the P-type and N-type conductive regions and the isolation region to the sub-micron level, thereby improving the lateral transport capability of charge carriers on the backside and increasing the fill factor to a certain extent. Building upon this, a multi-layer passivation stack structure is further fabricated on the polished isolation region surface, such as sequentially depositing an alumina layer, a high-refractive-index silicon nitride layer, and a low-refractive-index silicon nitride layer, to reduce optical losses on the backside. However, these structural optimizations targeting the backside of the battery have not effectively solved the UV-induced degradation problem of crystalline silicon solar cells, and the photoelectric conversion efficiency of the cells needs further improvement. Summary of the Invention

[0004] This disclosure provides a tunneling oxide passivated back contact battery and its preparation method to solve the problem of large ultraviolet-induced degradation and reduced photoelectric conversion efficiency in existing batteries.

[0005] In a first aspect, this disclosure provides a tunneling oxide passivated back contact battery, including a substrate layer, a passivation contact layer, a first doped semiconductor structure, a second doped semiconductor structure, a first electrode, and a second electrode; the substrate layer includes a light-receiving surface and a back-lighting surface disposed opposite to each other; the passivation contact layer is formed on the light-receiving surface side, and the surface of the passivation contact layer is shaped into a first textured structure having a plurality of first micro-units; in the direction from the light-receiving surface to the back-lighting surface, the cross-sectional size of the first micro-units gradually increases, and the doping concentration of the first micro-units gradually decreases; the first doped semiconductor structure and the second doped semiconductor structure are alternately formed on the back-lighting surface side, and the doping types of the first doped semiconductor structure and the second doped semiconductor structure are opposite; the first electrode is adapted to be disposed on the first doped semiconductor structure, and the second electrode is adapted to be disposed on the second doped semiconductor structure.

[0006] Beneficial effects: Firstly, by forming a passivation contact layer on the light-receiving side of the substrate, the surface passivation performance of the light-receiving surface is enhanced. The surface of the passivation contact layer is shaped into a first textured structure with multiple micro-units, which effectively enhances the light-trapping ability of the battery, causing light entering the substrate to be continuously reflected and refracted, thereby improving the photoelectric conversion efficiency. Furthermore, the first micro-units contain doped elements, making the passivation contact layer itself, composed of multiple first micro-units, a carrier for absorbing ultraviolet light, thus protecting the battery from ultraviolet-induced degradation, reducing the battery's sensitivity to ultraviolet light, and extending its service life. In addition, the textured morphology of the first micro-units improves the ultraviolet absorption rate of the doped elements, exhibiting good anti-ultraviolet effect. Secondly, in the direction from the light-receiving surface to the backlighting surface, the cross-sectional size of the first micro-unit gradually increases, while the doping concentration of the first micro-unit gradually decreases. This combination of cross-sectional size and doping concentration ensures that the side of the first micro-unit furthest from the substrate has a smaller cross-sectional size and a higher doping concentration, while the side closer to the substrate has a larger cross-sectional size and a lower doping concentration. Therefore, in the direction from the outside to the inside on the light-receiving surface, i.e., from the light-receiving surface to the backlighting surface, this disclosure forms a smoothly decreasing ultraviolet absorption curve, reducing the impact of the passivation contact layer on the quantum efficiency in the ultraviolet band and improving the overall performance of the battery. Finally, this disclosure utilizes a first electrode disposed on a first doped semiconductor structure and a second electrode disposed on a second doped semiconductor structure on the backlighting surface to output electrons and holes through the first and second electrodes respectively, achieving efficient photoelectric conversion.

[0007] In some alternative embodiments, the doping concentration of the first microcell on the side relatively far from the substrate layer ranges from 1E20 to 2E20 atoms / cm². 3 The doping concentration of the first micro-unit relative to the side closer to the substrate layer ranges from 1E19 to 2E19 atoms / cm². 3 .

[0008] Beneficial Effects: This disclosure limits the doping concentration of the first microcell to the above-mentioned range. The side of the first microcell relatively far from the substrate layer has the highest doping concentration to form a strong electric field region on that side. The side of the first microcell relatively close to the substrate layer has the lowest doping concentration to form a weak electric field region on that side. The strong electric field region preferentially captures and rapidly separates ultraviolet light to obtain photogenerated carriers, while the weak electric field region also collects carriers and reduces Auger recombination, thereby further refining the ultraviolet absorption curve. This improves the battery's UV resistance while reducing the impact of the passivation contact layer on the quantum efficiency in the ultraviolet band. Taking a pyramid-shaped first microcell as an example, at the apex, slope, and trough of the pyramid, due to the large size of the first microcell, the doping rate and final doping concentration of the doping element can effectively form a longitudinal and lateral concentration gradient coupled with the textured surface morphology under the influence of differences in exposure degree and radius of curvature.

[0009] In some optional embodiments, the tunneling oxide passivated back contact cell further includes a first surface doped layer and / or a second surface doped layer. The first surface doped layer is formed by extending inward from the light-receiving surface of the substrate to a first predetermined depth. The doping concentration of the first surface doped layer gradually decreases in the direction from the light-receiving surface to the back-lighting surface. The second surface doped layer is formed by extending inward from the back-lighting surface of the substrate to a second predetermined depth. The doping concentration of the second surface doped layer gradually decreases in the direction from the back-lighting surface to the light-receiving surface.

[0010] Beneficial Effects: Both the first and second surface-doped layers can be formed by surface doping of the substrate layer and are part of the substrate layer. Surface doping of the substrate layer reduces the surface contact resistivity, which helps to improve the overall carrier transport rate of the battery. Furthermore, the first surface-doped layer and the passivation contact layer are located on the light-receiving side of the substrate layer, while the second surface-doped layer is located on the back-light-receiving side. At least one of the first and second surface-doped layers works synergistically with the passivation contact layer to achieve efficient utilization of photons in the ultraviolet band and dynamic suppression of recombination loss. Moreover, since the doping concentration of the first surface-doped layer gradually decreases from the light-receiving side to the back-light-receiving side, and the doping concentration of the second surface-doped layer gradually decreases from the back-light-receiving side to the light-receiving side, while the doping concentration of the first micro-unit in the passivation contact layer gradually decreases from the light-receiving side to the back-light-receiving side, the doping concentration decreases from both sides of the substrate layer towards the center. This means the center of the substrate layer is lightly doped or even undoped. This concentration gradient design helps to improve the overall light absorption efficiency and lateral transport efficiency of photogenerated carriers in the substrate layer.

[0011] In some alternative implementations, the doping concentration of the first microcell relative to the side closer to the substrate is equal to the doping concentration of the substrate; and / or, the doping concentration of the second surface doped layer relative to the side closer to the substrate is equal to the doping concentration of the substrate.

[0012] Beneficial effects: By limiting the doping concentration of the first cell on the side relatively closer to the substrate to be equal to the doping concentration of the substrate, this disclosure efficiently and smoothly pushes photogenerated carriers to the substrate, thereby reducing the interface recombination rate and improving the short-circuit current and photoelectric conversion efficiency of the battery. Similarly, limiting the doping concentration of the second surface doped layer on the side relatively closer to the substrate to be equal to the doping concentration of the substrate has the same effect. When the above conditions are met simultaneously, the photoelectric conversion efficiency is greatly improved.

[0013] In some alternative implementations, the width of the first micro-unit near the substrate layer ranges from 0.8 to 1.5 μm, and the height of the first micro-unit ranges from 1.1 to 1.5 μm.

[0014] Beneficial effects: This disclosure uses a larger-sized first micro-unit to provide a molding basis for subsequent elemental gradient doping, exhibiting good doping gradient changes. This effectively resists ultraviolet-induced decay while constructing an internal electric field in the substrate layer, thereby improving the transport rate of photogenerated carriers.

[0015] In some alternative implementations, the side of the first micro-unit that is relatively far from the substrate layer is shaped into a ridge or strip parallel to the light-receiving surface.

[0016] Beneficial effects: The structure of this disclosure, which is contracted into ribs or stripes, not only reduces the surface stress concentration that leads to fragmentation, but also helps to accurately form the aforementioned gradient change of doping concentration.

[0017] In some alternative implementations, the backlight surface includes a first region, a second region, and an isolation region separating the first region and the second region, wherein a first doped semiconductor structure is adapted to be formed on the first region, a second doped semiconductor structure is adapted to be formed on the second region, and the isolation region is configured as a polished structure.

[0018] Beneficial effects: The present disclosure configures the isolation region as a polished structure. The first region and the second region can be either a velvety surface or a polished surface. In this way, the surface of the isolation region is flat and smooth, which helps to improve the passivation effect and reduce the interfacial recombination rate.

[0019] In some alternative embodiments, the first region is relatively higher than the second region in the thickness direction of the substrate layer, and the height difference between the isolation region and the second region ranges from 2.5 to 4.5 μm.

[0020] Beneficial effects: First, this disclosure utilizes a design where the first region is higher than the second region, combined with a process where the first region is P-type doped and the second region is N-type doped. This allows the P-type doped region, which has weaker carrier transport performance than the N-type doped region, to have a larger doped area, helping to balance the carrier transport effects of both and improve the photoelectric conversion efficiency of the battery. Second, this disclosure limits the minimum height difference to 2.5 μm to ensure sufficient physical isolation between the isolation region and the second region, preventing short circuits between the first and second regions and providing a relatively flat foundation for subsequent film deposition. The maximum height difference is limited to 4.5 μm to avoid excessive height difference increasing the lateral transport distance of photogenerated carriers, leading to a significant decrease in the fill factor. Limiting the height difference within the above range helps to balance optical and electrical performance, offering advantages of high reflectivity and low resistivity, improving the fill factor of the battery, and thus enhancing the photoelectric conversion efficiency.

[0021] In some alternative embodiments, the tunneling oxide passivated back contact cell further includes a first passivation antireflection layer and a second passivation antireflection layer. The first passivation antireflection layer is formed on the light-receiving surface of the substrate and covers the passivation contact layer, while the second passivation antireflection layer is formed on the back-light surface of the substrate.

[0022] Beneficial effects: This disclosure uses a first passivation and antireflection layer and a second passivation and antireflection layer to achieve passivation and antireflection effects on the first and second surfaces of a crystalline silicon solar cell, thereby reducing the recombination loss of photogenerated carriers, increasing the open-circuit voltage and fill factor, coupling more sunlight into the substrate layer, increasing light absorption, and improving the photoelectric conversion efficiency of the cell.

[0023] Secondly, this disclosure also provides a method for fabricating a tunneling oxide passivated back contact battery, comprising: providing a substrate layer, the substrate layer including a light-receiving surface and a back-lighting surface disposed opposite to each other; forming a passivation contact layer, the passivation contact layer being formed on one side of the light-receiving surface, the surface of the passivation contact layer being shaped into a first textured structure having a plurality of first micro-units; in a direction from the light-receiving surface toward the back-lighting surface, the cross-sectional size of the first micro-units gradually increases, and the doping concentration of the first micro-units gradually decreases; forming a first doped semiconductor structure and a second doped semiconductor structure, the first doped semiconductor structure and the second doped semiconductor structure being alternately formed on one side of the back-lighting surface, and the doping types of the first doped semiconductor structure and the second doped semiconductor structure being opposite; forming a first electrode and a second electrode, the first electrode being adapted to be disposed on the first doped semiconductor structure, and the second electrode being adapted to be disposed on the second doped semiconductor structure.

[0024] Beneficial effects: The present invention forms a passivation contact layer on a substrate layer. The surface of the passivation contact layer is texturized and doped to form a first textured structure with a doping concentration gradient. The first textured structure has multiple first micro-units with doping concentration gradually decreasing from the outside to the inside. This makes the passivation contact layer with multiple first micro-units on its surface itself a carrier for absorbing ultraviolet rays, which can effectively reduce the ultraviolet-induced degradation of the battery, thereby improving the battery's lifespan and photoelectric conversion efficiency. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This diagram illustrates the structure of the first surface doped layer, passivation contact layer, and protective layer after their formation in an embodiment of this disclosure. Figure 2 An electron microscope image of the ridges in the first micro-unit of this disclosure embodiment is shown; Figure 3 This diagram illustrates the structure of the first initially doped semiconductor structure after its formation in an embodiment of this disclosure. Figure 4 This diagram illustrates the structure of the first doped semiconductor structure after its formation in an embodiment of the present disclosure. Figure 5 This diagram illustrates the structure of the second initially doped semiconductor structure after its formation in an embodiment of this disclosure. Figure 6 A schematic diagram of the structure after the formation of the second doped semiconductor structure in an embodiment of this disclosure is shown; Figure 7 This diagram illustrates the structure of the first passivation antireflection layer and the second passivation antireflection layer after their formation in an embodiment of this disclosure. Figure 8 A schematic diagram of the structure after the first electrode and the second electrode are formed in an embodiment of this disclosure is shown.

[0027] Explanation of reference numerals in the attached figures: 1. Substrate layer; 2. Passivation contact layer; 21. First microcell; 211. Rib; 3. First doped semiconductor structure; 31. First tunneling layer; 310. First initial tunneling layer; 32. First doped polysilicon layer; 320. First initial doped polysilicon layer; 33. Borosilicate glass layer; 330. Initial borosilicate glass layer; 4. Second doped semiconductor structure; 41. Second tunneling layer; 410. Second initial tunneling layer; 42. Second doped polysilicon layer; 420. Second initial doped polysilicon layer; 43. Phosphosilicate glass layer; 430. Initial phosphosilicate glass layer; 5. First electrode; 6. Second electrode; 7. First surface doped layer; 8. Second surface doped layer; 9. First passivation antireflection layer; 10. Second passivation antireflection layer; 11. Protective layer; a. First region; b. Second region; c. Isolation region. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0029] refer to Figures 1 to 8 This disclosure provides a tunnel oxide passivated back contact battery (TBC battery), including a substrate layer 1, a passivation contact layer 2, a first doped semiconductor structure 3, a second doped semiconductor structure 4, a first electrode 5, and a second electrode 6; the substrate layer 1 includes a light-receiving surface and a back-lighting surface disposed opposite to each other; the passivation contact layer 2 is formed on the light-receiving surface, and the surface of the passivation contact layer 2 is formed into a first textured structure having a plurality of first micro-units 21; in the direction from the light-receiving surface to the back-lighting surface, the cross-sectional size of the first micro-units 21 gradually increases, and the doping concentration of the first micro-units 21 gradually decreases; the first doped semiconductor structure 3 and the second doped semiconductor structure 4 are alternately formed on the back-lighting surface, and the doping types of the first doped semiconductor structure 3 and the second doped semiconductor structure 4 are opposite; the first electrode 5 is adapted to be disposed on the first doped semiconductor structure 3, and the second electrode 6 is adapted to be disposed on the second doped semiconductor structure 4.

[0030] For example, the substrate layer 1 is configured as an N-type silicon wafer, and the passivation contact layer 2 is located on the light-receiving surface of the N-type silicon wafer. The passivation contact layer 2 can be part of the N-type silicon wafer, that is, no additional film layer is needed, thus improving light transmittance. In the first doped semiconductor structure 3 and the second doped semiconductor structure 4, one of them is configured as a P-type doped structure, and the other is configured as an N-type doped structure. The first doped semiconductor structure 3 and the second doped semiconductor structure 4 can respectively improve the conductivity of the substrate layer 1 by doping with boron or phosphorus, thereby increasing the concentration and mobility of photogenerated carriers, reducing recombination losses, and ultimately improving the photoelectric conversion efficiency of the battery.

[0031] In summary, the tunneling oxide passivated back contact solar cell disclosed herein first enhances the surface passivation performance of the light-receiving surface by forming a passivation contact layer 2 on the light-receiving side of the substrate layer 1. The surface of the passivation contact layer 2 is shaped into a first textured structure with multiple micro-units, which effectively enhances the light-trapping ability of the cell, causing light entering the substrate layer 1 to be continuously reflected and refracted, thereby improving the photoelectric conversion efficiency. Furthermore, the first micro-units 21 contain doped elements, making the passivation contact layer 2, composed of multiple first micro-units 21, itself a carrier for absorbing ultraviolet light, thus protecting the cell from ultraviolet-induced degradation (UV-induced degradation), reducing the cell's sensitivity to ultraviolet light, and extending its service life. In addition, the textured morphology of the first micro-units 21 improves the UV absorption rate of the doped elements, exhibiting good UV resistance. Secondly, in the direction from the light-receiving surface to the backlighting surface, the cross-sectional size of the first micro-unit 21 gradually increases, and the doping concentration of the first micro-unit 21 gradually decreases. This combination of cross-sectional size and doping concentration ensures that the first micro-unit 21 has a smaller cross-sectional size and higher doping concentration on the side farther from the substrate 1, and a larger cross-sectional size and lower doping concentration on the side closer to the substrate 1. Therefore, in the direction from the outside to the inside on the light-receiving surface, i.e., from the light-receiving surface to the backlighting surface, this disclosure forms a smoothly decreasing ultraviolet absorption curve, reducing the impact of the passivation contact layer 2 on the quantum efficiency of the ultraviolet band and improving the overall performance of the battery. Finally, this disclosure utilizes a first electrode 5 disposed on the first doped semiconductor structure 3 and a second electrode 6 disposed on the second doped semiconductor structure 4 on the backlighting surface, outputting electrons and holes through the first electrode 5 and the second electrode 6 respectively, achieving efficient photoelectric conversion.

[0032] like Figure 1 As shown, in some embodiments, the width of the first micro-unit 21 near the substrate 1 ranges from 0.8 to 1.5 μm, for example, the width w can be 0.8 μm, 1.2 μm, 1.5 μm, etc., and the height of the first micro-unit 21 ranges from 1.1 to 1.5 μm, for example, the height h can be 1.1 μm, 1.3 μm, 1.5 μm, etc.

[0033] Compared to the small-sized textured units in related technologies, such as textured units with a width range of 0.8~1.2 μm and a height range of 0.9~1.1 μm, this disclosure uses a larger-sized first micro-unit 21 to provide a molding basis for subsequent elemental gradient doping, exhibiting good doping gradient changes. This effectively resists ultraviolet-induced decay while constructing an internal electric field within the substrate layer 1, thereby improving the transport rate of photogenerated carriers.

[0034] In some embodiments, the doping concentration of the first microunit 21 relative to the side furthest from the substrate 1 ranges from 1E20 to 2E20 atoms / cm². 3 For example, 1E20 atoms / cm 3 1.5E20 atoms / cm 3 2E20 atoms / cm 3 The doping concentration of the first microunit 21 relative to the side closer to the substrate 1 ranges from 1E19 to 2E19 atoms / cm². 3 For example, 1E19 atoms / cm 3 1.5E19 atoms / cm 3 2E19 atoms / cm 3 .

[0035] This disclosure specifies that the doping concentration of the first micro-unit 21 is within the aforementioned range. The side of the first micro-unit 21 relatively far from the substrate layer 1 has the highest doping concentration, forming a strong electric field region on this side. The side of the first micro-unit 21 relatively close to the substrate layer 1 has the lowest doping concentration, forming a weak electric field region on this side. The strong electric field region preferentially captures and rapidly separates ultraviolet light to obtain photogenerated carriers, while the weak electric field region also collects carriers and reduces Auger recombination, thereby further refining the ultraviolet absorption curve. This improves the battery's UV resistance while reducing the impact of the passivation contact layer 2 on the quantum efficiency of the ultraviolet band. Taking a pyramid shape for the first micro-unit 21 as an example, at the apex, slope, and valley of the pyramid, due to the large size of the first micro-unit 21, the doping rate and final doping concentration of the doped elements can effectively form longitudinal and lateral concentration gradients coupled with the textured surface morphology under the influence of differences in exposure degree and radius of curvature.

[0036] In some embodiments, such as Figure 1 and Figure 2As shown, the side of the first micro-unit 21 furthest from the substrate layer 1 is shaped into a ridge 211 or strip-shaped surface parallel to the light-receiving surface. Compared to the conventional scheme where the first micro-unit 21 contracts outward to a sharp vertex, this structure of contracting into a ridge 211 or strip-shaped surface not only reduces surface stress concentration leading to fragmentation, but also helps to accurately form the aforementioned gradient change in doping concentration. For example, the first micro-unit 21 can be shaped into one or more of a pyramid structure, an inverted pyramid structure, or a pyramidal structure. Taking the first micro-unit 21 as a pyramid structure as an example, the adjacent first micro-units 21 form a groove. In the direction from the backlight surface to the light-receiving surface, the size of the first micro-unit 21 gradually shrinks into a rib 211 or a strip surface. The rib 211 is configured as a line with a small width, and the strip surface is configured as a plane with a preset width. Combined with the above-mentioned design of the doping concentration gradient arrangement, the rib 211 or strip surface has the highest doping concentration, forming a strong electric field region, which enhances the potential field of the battery. When the incident light reaches the strong electric field region, it is quickly converted into photogenerated carriers, thereby further improving the ultraviolet-induced decay.

[0037] In some embodiments, such as Figure 3 As shown, the tunneling oxide passivated back contact battery further includes a first surface doped layer 7 and / or a second surface doped layer 8. The first surface doped layer 7 is formed by extending inward from the light-receiving surface of the substrate layer 1 to a first preset depth. In the direction from the light-receiving surface to the back-lighting surface, the doping concentration of the first surface doped layer 7 gradually decreases. The second surface doped layer 8 is formed by extending inward from the back-lighting surface of the substrate layer 1 to a second preset depth. In the direction from the back-lighting surface to the light-receiving surface, the doping concentration of the second surface doped layer 8 gradually decreases.

[0038] In other words, this disclosure forms a structure with a doping concentration gradient in the shallow regions of both the light-receiving and back-light-receiving surfaces of the substrate 1. A first surface doped layer 7 is disposed in the shallow region of the light-receiving surface, i.e., below the first textured structure, and a second surface doped layer 8 is disposed in the shallow region of the back-light-receiving surface. Specifically, both the first surface doped layer 7 and the second surface doped layer 8 can be formed by surface doping of the substrate 1 and are part of the substrate 1. Surface doping of the substrate 1 reduces the surface contact resistivity, which helps to improve the overall carrier transport rate of the battery. In addition, the first surface doped layer 7 and the passivation contact layer 2 are located on the light-receiving surface of the substrate 1, and the second surface doped layer 8 is located on the back-light-receiving surface of the substrate 1. At least one of the first surface doped layer 7 and the second surface doped layer 8 works in conjunction with the passivation contact layer 2 to achieve efficient utilization of photons in the ultraviolet band and dynamic suppression of recombination loss. Furthermore, since the doping concentration of the first surface doped layer 7 gradually decreases from the light-receiving surface to the back-light-receiving surface, the doping concentration of the second surface doped layer 8 gradually decreases from the back-light-receiving surface to the light-receiving surface, and the doping concentration of the first micro-unit 21 in the passivation contact layer 2 gradually decreases from the light-receiving surface to the back-light-receiving surface, the doping concentration decreases from both sides of the substrate layer 1 towards the center. That is, the center of the substrate layer 1 is lightly doped or even undoped. This concentration gradient design helps to improve the overall light absorption efficiency and the lateral transport efficiency of photogenerated carriers of the substrate layer 1.

[0039] In some other embodiments, the tunneling oxide passivated back contact battery may include only the first surface doped layer 7. In other embodiments, the tunneling oxide passivated back contact battery may include only the second surface doped layer 8. It is understood that, compared to these two designs, the tunneling oxide passivated back contact battery exhibits optimal performance when it includes both the first surface doped layer 7 and the second surface doped layer 8. Specifically, the first surface doped layer 7 is formed by phosphorus diffusion, and the second surface doped layer 8 is formed by boron diffusion, thereby creating a built-in electric field with enhanced potential field. Electrons and holes are rapidly separated by the strong electric field and are separated and collected before they have time to recombine, significantly improving the battery's short-circuit current and open-circuit voltage.

[0040] It is understandable that when phosphorus doping is performed on the substrate layer 1, in addition to forming the first surface doped layer 7 and the passivation contact layer 2, a protective layer 11 is also formed on the surface of the passivation contact layer 2, and the protective layer 11 is configured as a phosphorus silicon glass layer.

[0041] In some embodiments, the doping concentration of the first microcell 21 relative to the side closer to the substrate 1 is equal to the doping concentration of the substrate 1; and / or, the doping concentration of the second surface doped layer 8 relative to the side closer to the substrate 1 is equal to the doping concentration of the substrate 1.

[0042] In other words, by limiting the doping concentration of the first cell relative to the substrate 1 to be equal to the doping concentration of the substrate 1, this disclosure efficiently and smoothly pushes photogenerated carriers to the substrate 1, thereby reducing the interface recombination rate and improving the short-circuit current and photoelectric conversion efficiency of the battery. Similarly, limiting the doping concentration of the second surface doped layer 8 relative to the substrate 1 to be equal to the doping concentration of the substrate 1 has the same effect. When the above conditions are met simultaneously, the photoelectric conversion efficiency is greatly improved.

[0043] In some embodiments, the doping concentration of the first surface doped layer 7 is 1E19~2E19 atoms / cm². 3 For example, 1E19 atoms / cm 3 1.5E19 atoms / cm 3 2E19 atoms / cm 3 Furthermore, the highest concentration of the first surface doped layer 7 is lower than the lowest concentration of the first micro-unit 21. Therefore, in the direction from the light-receiving surface to the backlighting surface, the concentrations of the first micro-unit 21 and the first surface doped layer 7 are set in a stepped manner. Of course, the maximum concentration of the first surface doped layer 7 can also be approximately equal to the lowest concentration of the first micro-unit 21, thus forming a smooth gradient change.

[0044] like Figures 4 to 8 As shown, the backlight surface includes a first region a, a second region b, and an isolation region c separating the first region a and the second region b. The first region a is suitable for forming a first doped semiconductor structure 3, the second region b is suitable for forming a second doped semiconductor structure 4, and the isolation region c is configured as a polished structure.

[0045] In this disclosure, the isolation region c is configured as a polished structure, and the first region a and the second region b can be either a velvety surface or a polished surface. In this way, the smooth and flat surface of the isolation region c helps to improve the passivation effect and reduce the interfacial recombination rate.

[0046] Specifically, the first doped semiconductor structure 3 can be configured as a P-type doped semiconductor structure, and the second doped semiconductor structure 4 can be configured as an N-type doped semiconductor structure. The first doped semiconductor structure 3 includes a first tunneling layer 31, a first doped polysilicon layer 32, and a borosilicate glass layer 33 stacked sequentially. The second doped semiconductor layer includes a second tunneling layer 41, a second doped polysilicon layer 42, and a phosphosilicate glass layer 43 stacked sequentially.

[0047] In some embodiments, such as Figure 6As shown, in the thickness direction of the substrate layer 1, the first region a is relatively higher than the second region b. The height difference H between the isolation region c and the second region b ranges from 2.5 to 4.5 μm, for example: 2.5 μm, 3.5 μm, 4.5 μm, etc. First, this disclosure utilizes the design of the first region a being higher than the second region b, combined with the process of the first region a being P-type doped and the second region b being N-type doped, so that the P-type doped region, whose carrier transport performance is relatively weaker than that of the N-type doped region, has a larger doping area, which helps to balance the carrier transport effect of the two regions and improve the photoelectric conversion efficiency of the battery. Second, this disclosure limits the minimum value of the height difference H to 2.5 μm to ensure that the isolation region c and the second region b have sufficient physical isolation, prevent the first region a and the second region b from short-circuiting, and provide a relatively flat foundation for subsequent film deposition. The maximum value of the height difference H is limited to 4.5 μm to avoid an excessively large height difference H increasing the lateral transport distance of photogenerated carriers, which would lead to a significant decrease in the fill factor. This disclosure limits the height difference H within the aforementioned range, which helps to balance optical and electrical performance, has the advantages of high reflectivity and low resistivity, improves the fill factor of the battery, and thus improves the photoelectric conversion efficiency.

[0048] like Figure 6 and Figure 7 As shown, the height difference between the first region a and the second region b refers to the height difference on the substrate layer 1. The thickness of the first region a does not include the thickness of the first doped semiconductor structure 3 and the thickness of the first passivation antireflection layer 9 and the second passivation antireflection layer 10 mentioned later. Similarly, the thickness of the second region b does not include the thickness of the second doped semiconductor structure 4 and the thickness of the second passivation antireflection layer 10. Likewise, the height difference H between the isolation region c and the second region b refers to the height difference H on the substrate layer 1. The thickness of the second region b does not include the thickness of the second doped semiconductor structure 4 and the thickness of the first passivation antireflection layer 9 and the second passivation antireflection layer 10 mentioned later.

[0049] like Figure 7 and Figure 8 As shown, the tunneling oxide passivated back contact solar cell further includes a first passivation antireflection layer 9 and a second passivation antireflection layer 10. The first passivation antireflection layer 9 is formed on the light-receiving surface of the substrate layer 1 and covers the passivation contact layer 2. The second passivation antireflection layer 10 is formed on the back-light-receiving surface of the substrate layer 1. This disclosure uses the first passivation antireflection layer 9 and the second passivation antireflection layer 10 to achieve passivation and antireflection effects on the first and second surfaces of the crystalline silicon solar cell, reducing the recombination loss of photogenerated carriers, improving the open-circuit voltage and fill factor, coupling more sunlight into the substrate layer 1, increasing light absorption, and improving the photoelectric conversion efficiency of the cell.

[0050] refer to Figures 1 to 8This disclosure also provides a method for preparing a tunneling oxide layer passivated back contact battery, which is used to prepare the above-mentioned tunneling oxide layer passivated back contact battery. The preparation method specifically includes the following steps: S100, such as Figure 1 As shown. A substrate layer 1 is provided, which includes a light-receiving surface and a backlight surface disposed opposite to each other.

[0051] For example, the substrate 1 is configured as an N-type silicon wafer.

[0052] S200, a passivation contact layer 2 is formed on the light-receiving side. The surface of the passivation contact layer 2 is shaped into a first textured structure with multiple first micro-units 21. In the direction from the light-receiving side to the backlight side, the cross-sectional size of the first micro-unit 21 gradually increases and the doping concentration of the first micro-unit 21 gradually decreases.

[0053] The preparation method also includes: forming a first surface doped layer 7 on one side of the light-receiving surface.

[0054] For example, a wet process is first used to pre-treat the silicon wafer by texturing, resulting in a first initial texturized structure on the light-receiving and back-light-receiving surfaces. This eliminates mechanical damage to the silicon wafer during the cutting process and improves the uniformity of subsequent film formation. The polishing solution used in the wet process is a mixture of potassium hydroxide and texturing additives, with a temperature range of 75℃~85℃ and a texturing time of 200~400 s. In the first initial texturized structure obtained by the wet process, the width of the base of the first micro-unit 21 ranges from 0.8 to 1.5 μm, the height of the first micro-unit 21 ranges from 1.1 to 1.5 μm, and the refractive index is 8%~10%. Then, a tube furnace is used to perform phosphorus doping on the texturing-prepared N-type silicon wafer, thereby forming a first surface doped layer 7, a passivation contact layer 2, and a protective layer 11. The protective layer 11 is configured as a phosphorus silicon glass layer 43. The first surface doped layer 7, the passivation contact layer 2, and the protective layer 11 constitute the phosphorus doping pre-surface field. Then, the first surface doped layer 7, the passivation contact layer 2, and the protective layer 11 deposited on the backlight surface and sidewalls are removed by a wet chain machine, for example, using hydrofluoric acid (HF) or nitric acid (HNO3) as the etching liquid. The first preset depth of the first surface doped layer 7 is 200 nm, and the thickness of the protective layer 11 is 40 nm.

[0055] Specifically, during phosphorus doping, the process temperature was 900℃, the duration was 3 hours, and the phosphorus doping concentration in the reaction chamber was 2.5E20~3.5E20 atoms / cm³. 3 For example, 3E20 atoms / cm 3Compared to conventional planar phosphorus-doped layers or undoped independent first textured structures, this disclosure achieves phosphorus doping in the first textured structure. In the direction from the light-receiving surface to the back-light-receiving surface, the doping concentration gradually decreases within the first micro-unit 21 of the first textured surface. A high-concentration strong electric field is formed on the side of the first micro-unit 21 that is relatively away from the substrate layer 1. The strong electric field can quickly separate photogenerated electrons and holes, so that ultraviolet light is instantly absorbed and separated on the side of the first micro-unit 21 that is relatively away from the substrate layer 1, and photogenerated carriers are generated, thereby further protecting the battery from ultraviolet-induced degradation.

[0056] S300, such as Figures 3 to 8 As shown, a first doped semiconductor structure 3 and a second doped semiconductor structure 4 are formed, which are alternately formed on one side of the backlight surface, and the doping types of the first doped semiconductor structure 3 and the second doped semiconductor structure 4 are opposite.

[0057] First, the preparation method also includes forming a second surface doped layer 8 on one side of the backlight surface.

[0058] like Figure 3 As shown, a first initial tunneling layer 310 and a first initial polysilicon layer are prepared on a substrate 1, and the first initial tunneling layer 310 and the first initial polysilicon layer are subjected to a boron doping process. The doping element penetrates into the backlight surface of the substrate 1 to a second preset depth to form a second surface doped layer 8. After boron diffusion, the first initial polysilicon layer forms a first initial doped polysilicon layer 320, and an initial borosilicate glass layer 330 is formed on the surface of the first initial doped polysilicon layer 320. The initial borosilicate glass layer 330, the first initial doped polysilicon layer 320 and the first initial tunneling layer 310 constitute a first initial doped semiconductor structure.

[0059] Specifically, this disclosure uses an LPCVD device to prepare a first initial tunneling layer 310 and a first initial doped polysilicon layer 320. The process conditions for preparing the first initial tunneling layer 310 are as follows: the reaction chamber temperature range is 580~650℃, for example 630℃; the deposition time range is 1000~5000 s, for example 2500 s; and the deposition thickness of the first initial tunneling layer 310 ranges from 2~8 nm, for example 6 nm. The deposition thickness of the first initial doped polysilicon layer 320 ranges from 120~190 nm, for example 170 nm; and the deposition temperature range is 550~580℃, for example 560℃. The thickness of the initial borosilicate glass layer 330 ranges from 40~70 nm, for example 50 nm. The second predetermined depth of the second surface doped layer 8 ranges from 250~550 nm, and the doping concentration of the second surface doped layer 8 relative to the side closer to the substrate layer 1 is 3E18 atoms / cm. 3The second preset depth range of the second surface doped layer 8 is greater than the first preset depth range of the first surface doped layer 7.

[0060] like Figure 3 and Figure 4 As shown. After forming the first initial doped semiconductor structure, laser grooving is performed on the second region b and the isolation region c of the backlight surface. Then, the initial borosilicate glass layer 330 on the light-receiving surface is removed by a chain-type borosilicate glass removal device. Then, a wet tank polishing solution is used to clean and remove the first initial doped polysilicon layer 320 and the first initial tunneling layer 310 on the light-receiving surface, as well as the second region b and the isolation region c. The first initial doped polysilicon layer 320 and the first initial tunneling layer 310 remaining on the first region a form the first doped polysilicon layer 32 and the first tunneling layer 31, resulting in the first doped semiconductor structure 3.

[0061] Specifically, after removing the first initial doped polysilicon layer 320 and the first initial tunneling layer 310 from the second region b and the isolation region c until the substrate layer 1 is exposed, a second textured structure (not shown in the figure) is formed after polishing. The second textured structure includes multiple second micro-units. The maximum width of the second micro-units near the substrate layer 1 ranges from 15 to 30 μm. For example, the width can be 15 μm, 20 μm, 25 μm, 30 μm, etc., and the polishing depth is 1.5 to 3.5 μm.

[0062] like Figure 5 As shown. After forming the first doped semiconductor structure 3, a second initial tunneling layer 410 and a second initial polysilicon layer are prepared, and the second initial tunneling layer 410 and the second initial polysilicon layer are subjected to phosphorus doping process. After phosphorus diffusion, the second initial polysilicon layer forms a second initial doped polysilicon layer 420. At the same time, an initial phosphosilicate glass layer 430 is formed on the surface of the second initial doped polysilicon layer 420. The initial phosphosilicate glass layer 430, the second initial doped polysilicon layer 420 and the second initial tunneling layer 410 constitute the second initial doped semiconductor structure.

[0063] Specifically, this disclosure uses a low-pressure chemical vapor deposition (LPCVD) apparatus to prepare a second initial tunneling layer 410 and a second initial doped polysilicon layer 420. The process conditions for preparing the second initial tunneling layer 410 are as follows: the reaction chamber temperature range is 580~650℃, the deposition temperature range is 550~580℃, the deposition time range is 1000~5000 s, and the deposition thickness of the first initial tunneling layer 410 ranges from 2~8 nm, for example, 2 nm. The deposition thickness of the second initial doped polysilicon layer 420 ranges from 120~190 nm, for example, 200 nm. The thickness of the initial phosphosilicate glass layer 430 ranges from 30~50 nm, for example, 50 nm.

[0064] like Figure 5 and Figure 6 As shown. After forming the second initial doped semiconductor structure, a second laser is applied to the isolation region c and the first region a. Then, the initial phosphosilicate glass layer 430 on the light-receiving surface is removed by a chain-type phosphosilicate glass removal device. A second cleaning and polishing process is then performed using a wet tank polishing solution to remove the second initial doped polysilicon layer 420 and the second initial tunneling layer 410 on the light-receiving surface, as well as in the first region a and the isolation region c, to obtain the second doped semiconductor structure 4.

[0065] After removing the second initial doped polysilicon layer 420 and the first initial tunneling layer 310 in the isolation region c, it is necessary to increase the removal amount inside the substrate layer 1, that is, to remove the second surface doped layer 8 located in the isolation region c, forming a height difference H between the isolation region c and the second region b. This design can not only ensure the lateral carrier transport rate, but also enhance the physical barrier of the isolation region c, and avoid short circuit between the first doped semiconductor structure 3 and the second doped semiconductor structure 4.

[0066] Secondly, such as Figure 7 As shown, the preparation method further includes: after forming the first doped semiconductor structure 3 and the second doped semiconductor structure 4, and before forming the first electrode 5 and the second electrode 6, forming the first passivation antireflection layer 9 and the second passivation antireflection layer 10.

[0067] For example, the formation of the first passivation antireflection layer 9 and the second passivation antireflection layer 10 may include an aluminum oxide layer and a silicon oxynitride layer. First, an aluminum oxide layer is deposited on both sides of the sample prepared in the aforementioned process using an atomic layer deposition (ALD) apparatus. The thickness of the aluminum oxide layer in the first passivation antireflection layer 9 is 4 nm, and the thickness of the aluminum oxide layer in the second passivation antireflection layer 10 is 4 nm. Then, a silicon oxynitride layer is deposited on the aluminum oxide layer using plasma-enhanced chemical vapor deposition (PECVD) equipment. The thickness of the silicon oxynitride layer in the first passivation antireflection layer 9 is 70-80 nm, and the thickness of the silicon oxynitride layer in the second passivation antireflection layer 10 is 80-120 nm. The total thickness of the first passivation antireflection layer 9 on the light-receiving surface ranges from 70-80 nm, and the total thickness of the second passivation antireflection layer 10 on the backlight surface ranges from 80-120 nm.

[0068] S400, such as Figure 8 As shown, a first electrode 5 and a second electrode 6 are formed. The first electrode 5 is adapted to be disposed on the first doped semiconductor structure 3, and the second electrode 6 is adapted to be disposed on the second doped semiconductor structure 4.

[0069] For example, the present disclosure forms the first electrode 5 and the second electrode 6 through processes such as screen printing, sintering, light injection, and laser-assisted sintering. Taking the example of the first electrode 5 being configured as the positive electrode and the second electrode 6 being configured as the negative electrode.

[0070] This disclosure involves forming a passivation contact layer 2 on a substrate layer 1. The surface of the passivation contact layer 2 is texturized and doped to form a first textured structure with a doping concentration gradient. The first textured structure has multiple first micro-units 21 with a doping concentration that gradually decreases from the outside to the inside. This makes the passivation contact layer 2 with multiple first micro-units 21 on its surface a carrier for absorbing ultraviolet light, which can effectively reduce the ultraviolet-induced degradation of the battery, thereby improving the battery's lifespan and photoelectric conversion efficiency.

[0071] Based on this, using the phosphorus doping concentration gradient in the battery as a variable, the electrical performance of the batteries from Example 1, Comparative Example 2, and Comparative Example 3 was tested, and the data are shown in the table below:

[0072] As can be seen from the table above, the battery in the embodiment is superior to Comparative Examples 1, 2 and 3 in terms of initial efficiency, that is, photoelectric conversion efficiency. In other words, the substrate layer 1 of the battery in this embodiment adopts a gradient doping concentration design, which can effectively improve the battery efficiency of the back contact solar cell.

[0073] Specifically, in Comparative Example 1, the concentration from the battery surface to the bulk remains constant at 1E20 atoms / cm³. 3 Without a built-in electric field driving force, photogenerated carriers rely solely on diffusion, resulting in high recombination losses and moderate UV-induced decay. Comparative Example 2 has a surface concentration of 1E21 atoms / cm². 3 The concentration in the body is 1E20 atoms / cm³ 3 In other words, if the surface concentration is too high, the surface peak exceeds the solid solubility, and the longitudinal gradient is extremely steep. Although this enhances the field passivation effect, Auger recombination is intensified, the band gap narrows, the reverse saturation current density increases, and ultraviolet-induced degradation is significant. Comparative Example 3 has a surface concentration of 5E19 atoms / cm³. 3 The concentration in the body is 1E18 atoms / cm³ 3 When the surface concentration is too low, the field passivation effect is insufficient, the short-wave response is poor, the reverse saturation current density is the highest, surface recombination is severe, and ultraviolet-induced degradation is the most severe. Example: Battery surface concentration 1E20 atoms / cm² 3 The concentration in the body is 1E19 atoms / cm³ 3 Therefore, the battery in this embodiment creates a built-in electric field by fabricating a shallow phosphorus diffusion concentration gradient on the front side, which rapidly separates photogenerated carriers within the ultraviolet light penetration depth, significantly reducing front-side recombination and lowering the reverse saturation current density to 28 fA / cm². 2 This improves the open-circuit voltage and fill factor; at the same time, phosphorus atoms form bonds with hydrogen atoms in SiNx:H (bond energy > 3.5 eV), suppressing hydrogen desorption and interface state proliferation caused by ultraviolet irradiation, thus improving the initial performance and long-term reliability of the battery.

[0074] Although embodiments of the present disclosure have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present disclosure, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A tunneling oxide passivated back contact battery, characterized in that, include: A substrate layer, the substrate layer comprising a light-receiving surface and a backlight surface disposed opposite to each other; A passivation contact layer is formed on one side of the light-receiving surface, and the surface of the passivation contact layer is shaped into a first textured structure having a plurality of first micro-units; in the direction from the light-receiving surface toward the backlight surface, the cross-sectional size of the first micro-units gradually increases, and the doping concentration of the first micro-units gradually decreases. A first doped semiconductor structure and a second doped semiconductor structure are alternately formed on one side of the backlight surface, and the doping types of the first doped semiconductor structure and the second doped semiconductor structure are opposite. A first electrode and a second electrode, wherein the first electrode is adapted to be disposed on the first doped semiconductor structure, and the second electrode is adapted to be disposed on the second doped semiconductor structure.

2. The tunneling oxide passivated back contact battery according to claim 1, characterized in that, The doping concentration of the first microunit on the side relatively far from the substrate layer ranges from 1E20 to 2E20 atoms / cm². 3 The doping concentration of the first micro-unit relative to the side closer to the substrate layer ranges from 1E19 to 2E19 atoms / cm². 3 .

3. The tunneling oxide passivated back contact battery according to claim 1, characterized in that, Also includes: The first surface doped layer is formed by extending inward from the light-receiving surface of the substrate layer to a first predetermined depth; In the direction from the light-receiving surface toward the backlight surface, the doping concentration of the first surface doped layer gradually decreases; And / or, The second surface doped layer is formed by extending inward from the backlight surface of the substrate layer to a second predetermined depth; the doping concentration of the second surface doped layer gradually decreases in the direction from the backlight surface to the light-receiving surface.

4. The tunneling oxide passivated back contact battery according to claim 3, characterized in that, The doping concentration of the first microcell relative to the side closer to the substrate is equal to the doping concentration of the substrate; and / or, the doping concentration of the second surface doped layer relative to the side closer to the substrate is equal to the doping concentration of the substrate.

5. The tunneling oxide passivated back contact battery according to claim 1, characterized in that, The width of the first micro-unit near the substrate layer ranges from 0.8 to 1.5 μm, and the height of the first micro-unit ranges from 1.1 to 1.5 μm.

6. The tunneling oxide passivated back contact battery according to claim 1, characterized in that, The side of the first micro-unit that is relatively far from the substrate layer is shaped into a ridge or strip parallel to the light-receiving surface.

7. The tunneling oxide passivated back contact battery according to any one of claims 1 to 6, characterized in that, The backlight surface includes a first region, a second region, and an isolation region separating the first region and the second region. The first region is adapted to form a first doped semiconductor structure, the second region is adapted to form a second doped semiconductor structure, and the isolation region is configured as a polished structure.

8. The tunneling oxide passivated back contact battery according to claim 7, characterized in that, In the thickness direction of the substrate layer, the first region is relatively higher than the second region, and the height difference between the isolation region and the second region ranges from 2.5 to 4.5 μm.

9. The tunneling oxide passivated back contact battery according to claim 7, characterized in that, Also includes: A first passivation antireflection layer and a second passivation antireflection layer are formed on the light-receiving surface of the substrate and cover the passivation contact layer, and the second passivation antireflection layer is formed on the backlight surface of the substrate.

10. A method for preparing a tunneling oxide passivated back contact battery, characterized in that, include: A substrate layer is provided, the substrate layer comprising a light-receiving surface and a backlight surface disposed opposite to each other; A passivation contact layer is formed on one side of the light-receiving surface, and the surface of the passivation contact layer is shaped into a first textured structure having a plurality of first micro-units; in the direction from the light-receiving surface toward the backlight surface, the cross-sectional size of the first micro-units gradually increases, and the doping concentration of the first micro-units gradually decreases. A first doped semiconductor structure and a second doped semiconductor structure are formed, the first doped semiconductor structure and the second doped semiconductor structure are alternately formed on one side of the backlight surface, and the doping types of the first doped semiconductor structure and the second doped semiconductor structure are opposite; A first electrode and a second electrode are formed, wherein the first electrode is adapted to be disposed on the first doped semiconductor structure, and the second electrode is adapted to be disposed on the second doped semiconductor structure.

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