A back-contact solar cell, its fabrication method and application

Abstract

This invention provides a back-contact solar cell, its fabrication method, and its application, relating to the field of solar cell technology. Specifically, the BC cell of this invention includes a silicon substrate, a light-modulating composite structure disposed on the light-receiving surface of the silicon substrate, and a passivated contact layer and interdigitated electrode structure disposed on the back-lighting surface of the silicon substrate; wherein, the light-modulating composite structure includes a dielectric light-modulating layer and a conductive light-modulating layer, the dielectric light-modulating layer comprising several dielectric electron layers, and the refractive index of the dielectric light-modulating layer varies in the thickness direction, and the conductive light-modulating layer comprises a transparent conductive oxide thin film. This invention improves the anti-reflection effect by setting a multilayer dielectric thin film stack with a gradient refractive index distribution, significantly improving the broadband light absorption efficiency; in addition, it has significant advantages in suppressing recombination loss on the light-receiving surface and enhancing the collection efficiency of photogenerated carriers, etc., in terms of photoelectric efficiency.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and more specifically, to a back-contact solar cell, its fabrication method, and its application. Background Technology

[0002] Back-contact (BC) solar cells are a type of photovoltaic cell technology where both the positive and negative electrodes are located on the back of the cell. With no metal grid lines obstructing the front, the cell's light-receiving area is significantly increased, optical losses are reduced, and thus photoelectric conversion efficiency is improved. In recent years, with breakthroughs in technologies such as laser patterning and passivated contacts, BC cells have gradually moved from the laboratory to industrialization, becoming one of the core technologies driving a new round of growth in the photovoltaic industry.

[0003] Existing BC (Browser-Based Cell) solar cells typically use N-type or P-type silicon substrates, forming interdigitated alternating P-type and N-type regions on the back side, with passivation contact structures and metal electrodes disposed in each region. The front side generally has one or more anti-reflection passivation layers to reduce light reflection loss and suppress surface recombination. However, as the efficiency of BC cells gradually approaches the theoretical limit of monocrystalline silicon cells, the traditional front passivation structure is increasingly revealing the following technical bottlenecks: First, there is the trade-off between light absorption and passivation performance. The front passivation layer of existing BC solar cells is typically silicon nitride (SiN). x While aluminum oxide (Al2O3) or its stacked structure can provide a certain anti-reflection effect, the absorption loss in the short wavelength band (350~450nm) is still relatively large. At the same time, the passivation layer has limited passivation ability for the field effect of charge carriers, making it difficult to achieve optimal light capture and minimum surface recombination at the same time.

[0004] Second, there is insufficient secondary utilization of incident light. The front structure of traditional BC cells only serves to reduce reflection and passivate. After the incident light penetrates the front structure, it enters the silicon substrate. The unabsorbed long-wavelength light passes through the entire thickness of the cell and escapes from the back, resulting in wasted light energy. Although some BC cells use a back-side polishing structure to enhance back reflection, the reflection efficiency is low and the reflected light re-enters the silicon substrate in the form of diffuse reflection, resulting in limited optical path gain.

[0005] Third, there is insufficient synergy between the front structure and the back interdigitated electrode. The front structure design of existing BC cells is relatively independent and does not effectively coordinate with the carrier collection requirements of the back interdigitated electrode. For example, during the migration of photogenerated carriers from the front to the back, recombination losses may occur due to the excessively long lateral diffusion path, especially near the P / N junction boundary region, where recombination losses are more significant.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a back-contact solar cell to address the problem that existing BC cells suffer from insufficient light energy utilization due to the difficulty in simultaneously achieving front-side light absorption and passivation performance.

[0008] A second objective of this invention is to provide a method for preparing the back-contact solar cell described above.

[0009] A third objective of the present invention is to provide the use of the aforementioned back-contact solar cell in solar power generation.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A back-contact solar cell, comprising: silicon substrate; A light-modulating composite structure is disposed on the light-receiving surface of the silicon substrate; A passivated contact layer and an interdigitated electrode structure are disposed on the back surface of the silicon substrate; The optical modulation composite structure includes a dielectric optical modulation layer and a conductive optical modulation layer. The dielectric optical modulation layer includes several dielectric electron layers, and the refractive index of the dielectric optical modulation layer varies in the thickness direction. The conductive optical modulation layer includes a transparent conductive oxide thin film.

[0011] In one embodiment, the light-modulating composite structure is provided with the dielectric light-modulating layer and the conductive light-modulating layer stacked sequentially in a direction away from the light-receiving surface.

[0012] In one embodiment, the number of dielectric electron layers in the dielectric optical modulation layer is ≥3, preferably equal to 3.

[0013] In one embodiment, the refractive index of the dielectric layer decreases in the direction away from the light-receiving surface; The refractive index of the dielectric layer closest to the silicon substrate is ≥3.0, and the refractive index of the dielectric layer furthest from the silicon substrate is <2.0.

[0014] In one embodiment, the refractive index is the same for any one of the dielectric layers; Along the direction away from the light-receiving surface, the refractive index of the dielectric optical modulation layer exhibits a stepwise decreasing trend.

[0015] In one embodiment, the dielectric optical modulation layer comprises light scattering particles; The light scattering particles include at least one of TiO2 nanoparticles, SiO2 nanoparticles, and ZnO nanoparticles, and the particle size of the light scattering particles is 20 nm to 100 nm.

[0016] In one embodiment, the transparent conductive oxide film includes at least one of indium tin oxide, aluminum-doped zinc oxide, boron-doped zinc oxide, and fluorine-doped tin dioxide.

[0017] In one embodiment, the passivation contact layer is a stacked structure of a tunneling oxide layer and doped polysilicon.

[0018] In one embodiment, the back-contact solar cell further includes an insulating isolation ring; The insulating isolation ring is disposed at the edge region of the light-receiving surface of the silicon substrate to control the conductive light modulation layer to have no electrical contact with the side of the silicon substrate.

[0019] A method for fabricating the back-contact solar cell includes the following steps: S1. Prepare a silicon substrate with a double-sided textured surface; S2. A patterned mask for a back interdigitated electrode structure is formed on the back surface of the silicon substrate. The P-region and N-region of the interdigitated electrode structure are prepared by ion implantation or high-temperature diffusion. Then, a passivation contact layer is deposited on the surface of the P-region and the N-region. S3. Layer-by-layer deposition is performed on the light-receiving surface of the silicon substrate to obtain several stacked dielectric electronic layers and a dielectric optical modulation layer; deposition and patterning are performed sequentially on the surface of the dielectric optical modulation layer to obtain a conductive optical modulation layer. S4. Electrodes are prepared on the surfaces of the P region and the N region by screen printing or electroplating to obtain a back-contact solar cell.

[0020] This invention provides a back-contact solar cell with a light-modulated composite structure. Compared with the prior art, the advantages of this invention are as follows: (1) The BC battery of the present invention significantly improves the broadband light absorption efficiency: On the one hand, by setting a multilayer dielectric thin film stack with a gradient refractive index distribution on the light-receiving surface, the average reflectivity in the broadband spectrum range of 350~1200nm can be reduced to below 5%, which is far superior to the traditional single-layer antireflection layer. On the other hand, by embedding nanoscale light scattering particles in the dielectric light modulation layer, the optical path of light in the near silicon surface region is significantly increased by utilizing the Mie scattering effect, especially the absorption enhancement effect of short wavelength light of 400~600nm is significant.

[0021] (2) The present invention can effectively suppress recombination loss on the light-receiving surface: On the one hand, the dielectric electron layer in the dielectric optical modulation layer that is in direct contact with the silicon substrate has a high fixed charge density, which can form field-effect passivation on the silicon surface and effectively suppress the recombination of photogenerated carriers on the light-receiving surface. On the other hand, by optimizing the interface quality of the multilayer dielectric film, the recombination rate on the light-receiving surface is greatly reduced, and photoluminescence imaging tests show that the luminescence intensity in the near-surface region is significantly higher than that of the traditional structure.

[0022] (3) The present invention can enhance the collection efficiency of photogenerated carriers: On the one hand, there is lateral potential guidance, that is, the conductive light control layer is patterned into electrically isolated conductive strips, and a lateral potential distribution is established on the light-receiving surface, which guides the photogenerated carriers to migrate to the edge of the silicon substrate or a specific region, shortens the longitudinal migration path of the carriers to the back electrode, and reduces recombination losses caused by lateral diffusion. On the other hand, there is synergy between the conductive light control layer and the back electrode, and each conductive strip forms an electrical coupling with the corresponding polarity electrode on the back, realizing the orderly collection of photogenerated carriers on the front side and improving the overall carrier collection efficiency.

[0023] (4) The present invention can improve the utilization rate of long-wavelength light energy: On the one hand, the internal reflection is enhanced by the back chamfer structure. Specifically, in the back interdigitated electrode structure, the bottom of the isolation trench between adjacent doped regions is provided with a chamfer structure. This structure not only effectively blocks the electrical crosstalk between the P-type and N-type regions, but also enhances the internal reflection effect on the incident long-wavelength light, so that the unabsorbed long-wavelength light is reflected back into the silicon substrate. On the other hand, the BC cell of the present invention improves the external quantum efficiency in the long-wavelength band; tests show that the external quantum efficiency in the 900~1200nm band is improved by about 8% compared with the traditional structure.

[0024] (5) The overall photoelectric conversion efficiency of the BC battery of the present invention is significantly improved; the open-circuit voltage reaches 748mV and the short-circuit current density reaches 42.8mA / cm² after standard testing. 2 The fill factor reaches 83.5%, and the photoelectric conversion efficiency reaches 26.75%. Compared with traditional BC cells (where the front side is only a single layer of SiN), this is significantly improved. x (Antireflection layer), the absolute value of conversion efficiency in this invention is increased by about 1.2 percentage points; compared with a single graded refractive index layer (without a conductive light control layer) or a single conductive layer structure, all performance indicators have significant advantages.

[0025] (6) The BC battery structure of the present invention is stable and reliable. On the one hand, an insulating isolation ring is provided at the edge of the light-receiving surface to effectively prevent electrical contact between the conductive light control layer and the side of the silicon substrate, avoid edge leakage, and improve the long-term stability and reliability of the battery. On the other hand, the back side adopts a passivated contact structure of tunneling oxide layer and doped polycrystalline silicon layer, which realizes excellent selective carrier transport and suppresses recombination loss in the metal contact area. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in 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 the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 A longitudinal cross-sectional structural diagram of the BC battery of Example 1 is provided; Figure 2 A partially enlarged schematic diagram of the light-modulated composite structure of the BC cell in Example 1 is provided; Figure 3 A top view schematic diagram of the patterned structure of the conductive light modulation layer of the BC battery in Embodiment 1 is provided; Figure 4 A partially enlarged cross-sectional view of the back interdigitated electrode structure of the BC battery of Example 1 is provided. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] A first aspect of the present invention is to provide a back-contact solar cell, comprising the following essential elements: (a) A silicon substrate having a light-receiving surface (i.e., the side surface exposed to light) and a back-lighting surface (i.e., the side surface not exposed to light) disposed opposite to each other; it is understood that the silicon substrate is the core of light absorption and carrier generation, and its composition includes N-type or P-type single crystal silicon.

[0032] (b) A light-modulating composite structure disposed on the light-receiving surface of the silicon substrate; the light-modulating composite structure includes a dielectric light-modulating layer and a conductive light-modulating layer, the dielectric light-modulating layer includes several dielectric electron layers, and the refractive index of the dielectric light-modulating layer varies in the thickness direction, the conductive light-modulating layer includes a transparent conductive oxide thin film.

[0033] In this invention, the dielectric optical modulation layer is a multilayer dielectric thin film stack with a gradient refractive index distribution, used to achieve gradient antireflection and surface field effect passivation in the wavelength range of 350nm~1200nm; the conductive optical modulation layer has lateral conductivity, used to form a lateral potential distribution on the light-receiving surface to guide photogenerated carriers to migrate to the edge of the silicon substrate or a specific collection area.

[0034] (c) A passivation contact layer and an interdigitated electrode structure are disposed on the back surface of the silicon substrate; in a typical embodiment, the passivation contact layer adopts a stacked structure of a tunneling oxide layer and doped polycrystalline silicon (SiO2 / poly-Si), and the quantum tunneling and collection of charge carriers are realized by utilizing the ultrathin silicon oxide tunneling layer; the interdigitated electrode structure is used to eliminate the light loss on the front side while efficiently collecting current.

[0035] In a preferred embodiment, the dielectric optical modulation layer is close to the silicon substrate, and the conductive optical modulation layer is not directly connected to the silicon substrate; it can also be understood that the optical modulation composite structure is provided with the dielectric optical modulation layer and the conductive optical modulation layer in sequence along the direction away from the light-receiving surface.

[0036] In a preferred embodiment, the number of dielectric electron layers in the dielectric optical modulation layer is ≥3, including but not limited to 3, 4, 5, etc.; in some more preferred embodiments, the dielectric optical modulation layer comprises three stacked dielectric electron layers.

[0037] In a preferred embodiment, the refractive index of the dielectric layer decreases along the direction away from the light-receiving surface. In one embodiment, the refractive index of the dielectric layer closest to the silicon substrate is ≥3.0, and the refractive index of the dielectric layer furthest from the silicon substrate is <2.0. In some optional embodiments, the refractive index of the dielectric layer closest to the silicon substrate includes, but is not limited to, any one or any two of the values ​​of 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, and 3.6, and the refractive index of the dielectric layer furthest from the silicon substrate includes, but is not limited to, any one or any two of the values ​​of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8.

[0038] As an optional implementation, the dielectric optical modulation layer comprises, in the direction away from the light-receiving surface, a first dielectric layer, a second dielectric layer, and a third dielectric layer arranged sequentially; the refractive index of the first dielectric layer is 3.0~3.5, the refractive index of the second dielectric layer is 2.0~2.5, and the refractive index of the third dielectric layer is 1.4~1.6, forming a gradient refractive index distribution from high to low.

[0039] In a preferred embodiment, the refractive index is the same for any one of the dielectric layers; in this case, the refractive index of the dielectric optical modulation layer decreases in a stepwise manner along the direction away from the light-receiving surface.

[0040] In a preferred embodiment, the dielectric optical modulation layer comprises an inorganic medium and light scattering particles, wherein the light scattering particles include at least one of TiO2 nanoparticles, SiO2 nanoparticles, and ZnO nanoparticles; in some embodiments, the inorganic medium includes at least one of silicon nitride, silicon oxynitride, silicon oxide, aluminum oxide, titanium oxide, and niobium pentoxide, more preferably at least one of silicon nitride, silicon oxynitride, and silicon oxide; in some embodiments, the particle size of the light scattering particles is 20 nm to 100 nm, including but not limited to any one or any two of 20, 30, 40, 50, 60, 70, 80, 90, and 100 (nm).

[0041] In a preferred embodiment, the total thickness of the dielectric optical modulation layer is 80nm~250nm, including but not limited to any one or any two of the following values: 80, 90, 100, 125, 150, 175, 200, 220, 240, and 250 (nm).

[0042] In a preferred embodiment, the thickness of the conductive light control layer is 50nm~150nm, including but not limited to any one or any two of the following values: 50, 60, 70, 75, 80, 90, 100, 120, 125, 130, 140, and 150 (nm).

[0043] In a preferred embodiment, the sheet resistance of the conductive light control layer is <100Ω / □ (unit: ohms per square), and the transmittance of the conductive light control layer in the wavelength range of 400nm~1200nm is >85%.

[0044] In a preferred embodiment, the transparent conductive oxide film includes, but is not limited to, indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), and fluorine-doped tin dioxide (FTO).

[0045] In a preferred embodiment, the conductive light control layer has a patterned arrangement on one side of the light-receiving surface, including a plurality of electrically isolated conductive strips; the conductive strips are arranged in parallel, and any one of the conductive strips is electrically coupled to an electrode in the interdigitated electrode structure.

[0046] In a preferred embodiment, the interdigitated electrode structure includes alternating first conductivity type doped regions and second conductivity type doped regions, and a first electrode and a second electrode respectively disposed on the surfaces of the first conductivity type doped regions and the second conductivity type doped regions. It is understood that numerous closely adjacent PN junctions are formed through the two conductivity type doped regions, and selective collection of charge carriers is achieved through the two types of electrodes. In one embodiment, the first conductivity type doped region and the second conductivity type doped region are N-type and P-type, respectively, and their main components are phosphorus-doped silicon and boron-doped silicon, respectively. The first electrode and the second electrode are independently obtained by screen printing using silver paste or silver-aluminum paste.

[0047] In a more preferred embodiment, the width ratio of the first conductivity type doped region to the second conductivity type doped region is 1~1.5:1.

[0048] In a more preferred embodiment, adjacent doped regions are separated by isolation trenches, and the bottom of the isolation trench between two adjacent doped regions is provided with a chamfer structure; the chamfer structure is recessed from the bottom surface of the trench toward the light-receiving surface, and its depth is 1.2 to 2 times the depth of the trench.

[0049] In a more preferred embodiment, the passivation contact layer covers the surfaces of the first conductivity type doped region and the second conductivity type doped region, that is, the passivation contact layer is provided on the upper surface of each P-type region and each N-type region; and it is understood that the passivation contact layer includes a tunneling oxide layer and doped polysilicon, wherein the tunneling oxide layer is close to the side of the doped region.

[0050] In a preferred embodiment, the back-contact solar cell further includes an insulating isolation ring, which is disposed at the edge region of the light-receiving surface of the silicon substrate. It is understood that the insulating isolation ring surrounds the peripheral region of the light-modulating composite structure to prevent electrical contact between the conductive light-modulating layer on the light-receiving surface and the side of the silicon substrate.

[0051] A second aspect of the present invention is to provide a method for fabricating a back-contact solar cell as described in the first aspect, which mainly includes the following steps: S1. Prepare a silicon substrate with a double-sided textured surface; S2. A patterned mask for a back interdigitated electrode structure is formed on the back surface of the silicon substrate. The P-region and N-region of the interdigitated electrode structure are prepared by ion implantation or high-temperature diffusion. Then, a passivation contact layer is deposited on the surface of the P-region and the N-region. S3. Layer-by-layer deposition is performed on the light-receiving surface of the silicon substrate to obtain several stacked dielectric electronic layers and a dielectric optical modulation layer; deposition and patterning are performed sequentially on the surface of the dielectric optical modulation layer to obtain a conductive optical modulation layer. S4. Electrodes are prepared on the surfaces of the P region and the N region by screen printing or electroplating to obtain a back-contact solar cell.

[0052] As a preferred embodiment, for step S1: providing an N-type or P-type monocrystalline silicon substrate raw material, and performing double-sided alkaline texturing on the silicon substrate to form a textured structure on the light-receiving side and the back-lighting side; it can be understood that by polishing in an alkaline solution to form texturing, the back-lighting side aims to reduce the surface recombination rate, optimize the uniformity of back-side film deposition to improve the passivation effect and double-sided ratio, and the front side significantly reduces the light reflectivity by increasing the number of light reflections, thereby maximizing the light absorption and utilization efficiency.

[0053] In a preferred embodiment, for step S3: a multilayer dielectric film with a gradient refractive index distribution is sequentially deposited on the light-receiving surface of the silicon substrate using plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD); simultaneously, a transparent conductive oxide film is formed on the surface of the dielectric light-modulating layer using magnetron sputtering or reactive plasma deposition.

[0054] As a preferred embodiment, in step S3: during the deposition of the dielectric light control layer, nanoscale light scattering particles are introduced simultaneously, and the light scattering particles are embedded in the dielectric film through co-deposition or surface self-assembly.

[0055] As a preferred embodiment, for step S3: the patterning process adopts laser etching or wet etching process, and the etching depth is precisely controlled to the interface between the conductive light control layer and the dielectric light control layer.

[0056] In a preferred embodiment, the preparation method may further include: coating an insulating material on the edge region of the light-receiving surface to form an insulating isolation ring.

[0057] A third aspect of the invention is to provide the use of the back-contact solar cell as described in the first aspect in solar power generation, including but not limited to civilian photovoltaic power generation equipment, photovoltaic integrated buildings, centralized solar power plants, and any non-existent innovative solar-powered equipment.

[0058] Example This embodiment provides a back-contact solar cell with a light-modulated composite structure.

[0059] like Figure 1 As shown, the back-contact solar cell includes: a silicon substrate 1, a light-modulating composite structure 2 disposed on the light-receiving surface 11 of the silicon substrate 1, and a back interdigitated electrode structure 3 and a passivation contact layer 4 disposed on the back-lighting surface 12 of the silicon substrate 1.

[0060] The silicon substrate 1 is an N-type single-crystal silicon wafer with a resistivity of 3 Ω·cm and a thickness of 150 μm. Both the light-receiving surface 11 and the back-lighting surface 12 are treated with alkali texturing to form a random pyramid textured surface structure to enhance the light-trapping effect.

[0061] The light-modulating composite structure 2 is disposed on the light-receiving surface 11, and its structure is as follows: Figure 2 As shown, it includes a dielectric light control layer 21 and a conductive light control layer 22 stacked sequentially along the direction away from the light-receiving surface.

[0062] The dielectric optical modulation layer 21 is a three-layer dielectric thin film stack with a graded refractive index distribution. The first dielectric layer 211 is SiN. xThe thin film (refractive index approximately 3.2, thickness 20 nm, x = 4 / 3) is in direct contact with the silicon substrate, providing good surface passivation and field effects. The second dielectric layer 212 is SiO2. x N y A thin film (refractive index approximately 2.3, thickness 40 nm, x = 0.8, y = 0.6) serves as a transition layer to achieve a gradient transition in refractive index. The third dielectric layer, 213, is SiO2. x A thin film (refractive index approximately 1.5, thickness 60 nm, x=2) serves as the top layer to further reduce reflectivity. This three-layer structure exhibits an average reflectivity of less than 5% over a broad spectral range of 350–1200 nm. Simultaneously, TiO2 nanoparticles with an average particle size of 40 nm are embedded in the dielectric optical modulation layer 21, enhancing the optical path length near the silicon surface region through the Mie scattering effect, particularly showing a significant enhancement in light absorption within the 400–600 nm wavelength range.

[0063] The conductive light control layer 22 is an aluminum-doped zinc oxide (AZO) thin film with a thickness of 80 nm, a sheet resistance of 80 Ω / □, and an average transmittance greater than 88% in the wavelength range of 400–1200 nm. For example... Figure 3 As shown, the conductive light control layer 22 is patterned by laser etching into multiple conductive strips 221 extending along a first direction (X direction in the figure) and arranged at equal intervals along a second direction (Y direction in the figure). Adjacent conductive strips are electrically isolated by isolation trenches 222. Each conductive strip 221 forms an electrical coupling with an electrode of the corresponding polarity on the back side, establishing a lateral potential gradient on the light-receiving surface. This guides photogenerated carriers to migrate towards the edge or a specific region, thereby shortening the longitudinal migration distance of carriers to the back electrode and reducing recombination losses.

[0064] like Figure 1 and Figure 4 As shown, the back interdigitated electrode structure 3 includes alternating P-type doped regions 31 (first conductivity type doped regions) and N-type doped regions 32 (second conductivity type doped regions), and P-electrodes 33 and N-electrodes 34 respectively disposed thereon. Isolation trenches 35 are provided between adjacent doped regions. A chamfered structure 351 is provided at the bottom of the isolation trench 35, which is recessed from the bottom surface of the trench towards the light-receiving surface, with a depth approximately 1.5 times the trench depth. This chamfered structure not only effectively blocks the diffusion of atoms between the P-type and N-type regions, but also enhances the internal reflection effect of the back side on incident long-wavelength light, causing unabsorbed long-wavelength light to be reflected back into the silicon substrate.

[0065] A passivation contact layer 4 is disposed between each doped region on the back side and the silicon substrate, including a tunneling oxide layer 41 (SiO2 with a thickness of 1.5 nm) and a doped polycrystalline silicon layer 42 (80 nm thick, with boron-doped polycrystalline silicon corresponding to P-type doped regions and phosphorus-doped polycrystalline silicon corresponding to N-type doped regions). This passivation contact structure achieves excellent selective carrier transport and effectively suppresses recombination losses in the metal contact region.

[0066] In addition, such as Figure 1 As shown, an insulating isolation ring 5 is provided at the edge region of the light-receiving surface 11 of the silicon substrate. It is formed by coating and curing epoxy resin insulating adhesive and is arranged around the periphery of the light-modulating composite structure 2 to prevent the conductive light-modulating layer 22 from making electrical contact with the side of the silicon substrate and causing edge leakage.

[0067] This embodiment also provides a method for fabricating a back-contact solar cell as described above, including the following steps: Step S1: Silicon substrate preparation and texturing; An N-type monocrystalline silicon wafer with a thickness of 150 μm and a resistivity of 2 Ω·cm was selected. Double-sided alkaline texturing was performed using KOH solution at a temperature of 80℃ for 15 minutes, forming a random pyramidal textured surface structure that reduced reflectivity to below 12%.

[0068] Step S2: Fabrication of the back-side doped region; A mask layer is deposited on the back surface of a silicon substrate, and an interdigitated mask pattern is formed by laser patterning. P-type and N-type doped regions are formed using boron ion implantation and phosphorus ion implantation processes, respectively, with an implantation energy of 40 keV and a dose of 3 × 10⁻⁶. 15 cm -2 The impurities were then activated by high-temperature annealing at 900°C for 30 minutes.

[0069] Step S3: Deposition of back passivation contact layer; A 1.5 nm thick tunneling oxide (SiO2) layer was deposited on the back side using PECVD, followed by an 80 nm thick intrinsic polycrystalline silicon layer. Boron diffusion doping was applied to the P-type doped regions, and phosphorus diffusion doping was applied to the N-type doped regions to form a doped polycrystalline silicon layer.

[0070] Step S4: Deposition of the front dielectric optical modulation layer; SiN was sequentially deposited on the light-receiving surface using the PECVD method. x Layer (20nm thick, refractive index 3.2), SiO x N y Layer (40 nm thick, refractive index 2.3) and SiO xLayer (60 nm thick, refractive index 1.5). During the deposition process, TiO2 nanoparticles with a particle size of 30 nm were introduced via a gas-carrying method to uniformly embed them into the dielectric film.

[0071] Step S5: Deposition and patterning of the front conductive light control layer; An 80 nm thick AZO thin film was deposited on a dielectric-optical modulation layer using magnetron sputtering. A picosecond laser etching system was then used to pattern the AZO film, forming electrically isolated conductive strips. The etching depth was precisely controlled to achieve an AZO / SiO2 ratio. x Interface, strip width 100μm, spacing 10μm.

[0072] Step S6: Back electrode fabrication; Metal electrodes are fabricated on the doped regions on the back side using screen printing or electroplating. Aluminum paste or silver-aluminum paste is used for the P-type electrodes, and silver paste is used for the N-type electrodes. The electrodes are sintered at 800℃ to form good ohmic contact.

[0073] Step S7: Edge insulation treatment; Epoxy resin insulating adhesive is applied to the edge area of ​​the light-receiving surface and then heat-cured to form an insulating isolation ring with a width of 2mm.

[0074] Step S8: Subsequent processes; This includes battery performance testing and sorting, such as photoluminescence detection, electroluminescence detection, and IV testing.

[0075] Comparative Example 1: The difference from the embodiment is that the light-receiving surface is only provided with a single layer of SiN. x The antireflection layer (75nm thick) does not have a light-modulating composite structure.

[0076] Comparative Example 2: The difference from the embodiment is that the dielectric optical modulation layer is a single refractive index SiN. x The layer did not employ a multilayer structure with a gradient refractive index.

[0077] Comparative Example 3: The difference from the embodiment is that no conductive light control layer is provided.

[0078] Test case The BC batteries prepared in the examples were subjected to performance testing under standard AM 1.5 illumination and 25°C conditions.

[0079] The test results are shown in Table 1. Compared with the traditional BC battery (with only a single layer of SiNx antireflection layer on the front), the open circuit voltage is increased by about 5mV, the short circuit current density is increased by about 1.2mA / cm², and the absolute value of the conversion efficiency is increased by about 1.2 percentage points.

[0080] Further photoluminescence imaging tests showed that the photomodulated composite structure of this invention effectively suppressed recombination loss on the light-receiving surface, especially with significantly higher luminescence intensity in the near-surface region compared to the control group. Long-wavelength light response tests indicated that, due to the enhanced internal reflection effect of the back chamfer structure, the external quantum efficiency of the battery in the 900–1200 nm wavelength range was improved by approximately 8%.

[0081] Table 1

[0082] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A back-contact solar cell, characterized in that, include: silicon substrate; A light-modulating composite structure is disposed on the light-receiving surface of the silicon substrate; A passivated contact layer and an interdigitated electrode structure are disposed on the back surface of the silicon substrate; The optical modulation composite structure includes a dielectric optical modulation layer and a conductive optical modulation layer. The dielectric optical modulation layer includes several dielectric electron layers, and the refractive index of the dielectric optical modulation layer varies in the thickness direction. The conductive optical modulation layer includes a transparent conductive oxide thin film.

2. The back-contact solar cell according to claim 1, characterized in that, Along the direction away from the light-receiving surface, the light-modulating composite structure is provided with the dielectric light-modulating layer and the conductive light-modulating layer stacked sequentially.

3. The back-contact solar cell according to claim 1, characterized in that, For the dielectric optical modulation layer, the number of dielectric electron layers is ≥3, preferably equal to 3.

4. The back-contact solar cell according to claim 1, characterized in that, The refractive index of the dielectric layer decreases along the direction away from the light-receiving surface. The refractive index of the dielectric layer closest to the silicon substrate is ≥3.0, and the refractive index of the dielectric layer furthest from the silicon substrate is <2.

0.

5. The back-contact solar cell according to claim 1, characterized in that, For any given dielectric layer, the refractive index within the layer is the same; Along the direction away from the light-receiving surface, the refractive index of the dielectric optical modulation layer exhibits a stepwise decreasing trend.

6. The back-contact solar cell according to claim 1, characterized in that, The dielectric optical modulation layer comprises light scattering particles; The light scattering particles include at least one of TiO2 nanoparticles, SiO2 nanoparticles, and ZnO nanoparticles, and the particle size of the light scattering particles is 20 nm to 100 nm.

7. The back-contact solar cell according to claim 1, characterized in that, The transparent conductive oxide film includes at least one of indium tin oxide, aluminum-doped zinc oxide, boron-doped zinc oxide, and fluorine-doped tin dioxide; And / or, the passivation contact layer is a stacked structure of a tunneling oxide layer and doped polysilicon.

8. The back-contact solar cell according to claim 1, characterized in that, The back-contact solar cell also includes an insulating isolation ring; The insulating isolation ring is disposed at the edge region of the light-receiving surface of the silicon substrate to control the conductive light modulation layer to have no electrical contact with the side of the silicon substrate.

9. A method for preparing a back-contact solar cell as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Prepare a silicon substrate with a double-sided textured surface; S2. A patterned mask for a back interdigitated electrode structure is formed on the back surface of the silicon substrate. The P-region and N-region of the interdigitated electrode structure are prepared by ion implantation or high-temperature diffusion. Then, a passivation contact layer is deposited on the surface of the P-region and the N-region. S3. Layer-by-layer deposition is performed on the light-receiving surface of the silicon substrate to obtain several stacked dielectric electronic layers and a dielectric optical modulation layer; deposition and patterning are performed sequentially on the surface of the dielectric optical modulation layer to obtain a conductive optical modulation layer. S4. Electrodes are prepared on the surfaces of the P region and the N region by screen printing or electroplating to obtain a back-contact solar cell.

10. Use of the back-contact solar cell as described in any one of claims 1 to 8 in solar power generation.

Images