Back contact crystalline silicon solar cell and method of manufacturing the same

Abstract

The application provides a back contact crystalline silicon solar cell and a preparation method thereof, relates to the technical field of solar cells, and aims to solve the problem of low photoelectric conversion rate of a back contact crystalline silicon solar cell in the prior art. The back contact crystalline silicon solar cell comprises a substrate and a doped structure arranged on the back surface of the substrate. The doping concentration of the doped structure exponentially attenuates along the thickness direction of the substrate to form a gradient energy band. In the thickness direction of the substrate, the doped structure comprises opposite top and bottom parts, the bottom part is close to the back surface of the substrate, and the projected area of the bottom part in the thickness direction of the substrate is greater than the projected area of the top part in the thickness direction of the substrate. The doped structure comprises P-type doped columns and N-type doped columns which are alternately and spacedly arranged. The doped structure in the form of a truncated pyramid array is constructed on the back surface of the cell, and the carrier distribution is optimized through the gradient energy band design, so that the photoelectric conversion rate is improved.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a back-contact crystalline silicon solar cell and its fabrication method. Background Technology

[0002] Back-contact (BC) crystalline silicon solar cells are one of the core technologies in the photovoltaic field. By designing all the electrodes on the back of the cell, light loss caused by shading of the front electrodes is eliminated, achieving high photoelectric conversion efficiency. They are widely used in large-scale photovoltaic power plants, distributed energy systems, rooftop photovoltaics, building-integrated photovoltaics, and other scenarios with high space utilization requirements.

[0003] In the fabrication process of back-contact crystalline silicon solar cells, photoelectric conversion efficiency is a key indicator for measuring cell performance. In related technologies, back-contact structure cells typically employ local doping to form p-type and n-type doped regions, and combine this with a back-side cross-finger electrode layout to enhance carrier collection capability.

[0004] However, in actual fabrication, several process factors severely restrict the photoelectric conversion efficiency of the solar cell. For example, in the doping process, the high temperature associated with high-energy laser doping easily induces lattice damage in the silicon wafer, leading to carrier recombination and a decrease in the photoelectric conversion efficiency. The interface between the p-type and n-type doped regions has a high density of defects and impurities, easily becoming the main region for carrier recombination, further exacerbating interface recombination and significantly limiting the photoelectric conversion efficiency. Furthermore, insufficient patterning precision of the back-side interdigitated electrodes may result in poor contact between the doped region and the electrode or localized leakage, affecting the effective collection of carriers. These factors collectively limit the photoelectric conversion efficiency of back-contact crystalline silicon solar cells. Summary of the Invention

[0005] In view of the above problems, this application provides a back-contact crystalline silicon solar cell and its preparation method to solve the problem of low photoelectric conversion efficiency of back-contact crystalline silicon solar cells in related technologies.

[0006] The embodiments of this application provide the following technical solutions:

[0007] This application provides a back-contact crystalline silicon solar cell, comprising: a substrate; and a doped structure disposed on the back side of the substrate, wherein the doping concentration of the doped structure decreases exponentially along the thickness direction of the substrate to form a gradient energy band; the doped structure includes an opposing top and bottom in the thickness direction of the substrate, the bottom being close to the back side of the substrate, and the projected area of ​​the bottom in the thickness direction of the substrate being larger than the projected area of ​​the top in the thickness direction of the substrate; the doped structure includes alternately spaced P-type doped pillars and N-type doped pillars.

[0008] In one embodiment of this application, an isolation trench is provided between adjacent P-type doped pillars and N-type doped pillars, and a dielectric material is disposed in the isolation trench.

[0009] In one embodiment of this application, an amorphous silicon carbide layer is further formed on the top.

[0010] In one embodiment of this application, the back-contact crystalline silicon solar cell further includes: a double-layer passivation structure; the double-layer passivation structure is disposed between the back side of the substrate and the doped structure, the double-layer passivation structure includes a first passivation layer and a second passivation layer stacked together, the first passivation layer being close to the back side of the substrate; the first passivation layer is a silicon oxide layer, and the second passivation layer is an aluminum oxide layer.

[0011] In one embodiment of this application, the back-contact crystalline silicon solar cell further includes: a textured structure; the textured structure is disposed on the front side of the substrate, and the surface of the textured structure away from the substrate includes a plurality of randomly distributed conical, pyramidal, or spherical micron-sized structures.

[0012] In one embodiment of this application, the width of the isolation groove is ≤5μm; the depth of the isolation groove is 0.5μm~1μm.

[0013] In one embodiment of this application, the thickness of the amorphous silicon carbide layer is 20nm~50nm; the bandgap of the amorphous silicon carbide layer is ≥1.8eV.

[0014] In one embodiment of this application, the doping concentration of the doped structure includes 1×10⁻⁶. 18 cm -3 ~1×10 20 cm -3 .

[0015] This application also provides a method for fabricating a back-contact crystalline silicon solar cell, used to fabricate the back-contact crystalline silicon solar cell described above, comprising:

[0016] A substrate is provided, and alternating P-type doped regions and N-type doped regions are defined on the back side of the substrate. Based on the P-type doped regions and the N-type doped regions, alternating P-type doped pillars and N-type doped pillars are formed on the back side of the substrate. In the thickness direction of the substrate, the doping concentration of the P-type doped pillars and the N-type doped pillars decreases exponentially to form a gradient energy band. Each P-type doped pillar and N-type doped pillar includes an opposing top and a bottom, the bottom being close to the back side of the substrate, and the projected area of ​​the bottom in the thickness direction of the substrate is greater than the projected area of ​​the top in the thickness direction of the substrate.

[0017] In one embodiment of this application, defining alternating P-type and N-type doped regions on the back side of the substrate includes: sequentially forming a silicon oxide layer and an aluminum oxide layer on the back side of the substrate to obtain a double-layer passivation structure; and using a laser to open windows in the double-layer passivation structure to obtain alternating P-type and N-type windows to define the P-type and N-type doped regions.

[0018] In one embodiment of this application, after forming alternately spaced P-type doped pillars and N-type doped pillars on the back side of the substrate, the method further includes: etching an isolation trench using the gap between adjacent P-type doped pillars and N-type doped pillars as a mask; and disposing of a dielectric material within the isolation trench.

[0019] In one embodiment of this application, after the dielectric material is disposed in the isolation trench, the method further includes: forming an amorphous silicon carbide layer on the top of the P-type doped pillar and the N-type doped pillar.

[0020] In one embodiment of this application, before defining the alternating P-type doped regions and N-type doped regions on the back side of the substrate, the method further includes: forming a textured structure on the front side of the substrate by a chemical etching method, wherein the surface of the textured structure away from the substrate includes a plurality of randomly distributed conical, pyramidal, or spherical micron-sized structures.

[0021] The back-contact crystalline silicon solar cell provided in this application has the following technical advantages:

[0022] By forming alternating P-type and N-type doped pillars on the back side of the substrate, a three-dimensional doped structure is formed in the thickness direction of the substrate. This transforms the pn junction interface from a two-dimensional plane into a tortuous and enlarged interface in three-dimensional space, providing more and closer paths for charge carriers to be captured and separated by the built-in electric field. This significantly improves the charge carrier collection efficiency, thereby enhancing the photoelectric conversion efficiency.

[0023] Meanwhile, the doping concentration of the P-type and N-type doped pillars decreases exponentially along the thickness direction of the substrate to form a gradient band. The gradient band structure ensures a strong, directional driving force along the entire path from the inside of the substrate to the back side, enabling carriers to be efficiently and quickly swept out of the semiconductor bulk region. This greatly reduces the probability of recombination due to excessive residence time in the bulk and at the contact interface, and significantly suppresses carrier recombination.

[0024] The tops of the P-type and N-type doped pillars are in contact with the metal electrode, and the high doping concentration at the top ensures the formation of a low-resistance ohmic contact to reduce energy loss. The lower doping concentration at the bottom of the P-type and N-type doped pillars means less lattice damage and defects, which is beneficial for achieving high-quality passivation and reducing the surface recombination rate. Therefore, the gradient band structure also achieves a balance between low contact resistance and high passivation quality, maximizing light absorption and carrier collection efficiency, and resulting in a significant improvement in photoelectric conversion efficiency.

[0025] Furthermore, the projected area of ​​the bottom of the P-type and N-type doped pillars along the thickness direction of the substrate is larger than the projected area of ​​the top of the P-type and N-type doped pillars along the thickness direction of the substrate, thus forming truncated pyramid-shaped P-type and N-type doped pillars. Reducing the contact area between the top and the metal electrode minimizes recombination losses in the metal contact region; increasing the contact area between the bottom and the back surface of the substrate forms a broad PN junction interface, providing a wider and more convenient collection entrance for charge carriers generated from various parts of the substrate, significantly improving charge carrier collection efficiency, and thus enhancing photoelectric conversion efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the structure of a back-contact crystalline silicon solar cell provided in an embodiment of this application. Figure 1 ;

[0028] Figure 2 A schematic diagram of the structure of a back-contact crystalline silicon solar cell provided in an embodiment of this application. Figure 2 .

[0029] Figure label:

[0030] 100-substrate;

[0031] 200-P type doped column;

[0032] 300-N type doped column;

[0033] 400 - Isolation Groove;

[0034] 500-Amorphous silicon carbide layer;

[0035] 600-Double-layer passivation structure;

[0036] 700-suede texture. Detailed Implementation

[0037] To make the above-mentioned objectives, features, and advantages of the embodiments of this application more apparent and understandable, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0038] refer to Figure 1 and Figure 2 The back-contact crystalline silicon solar cell provided in this application includes: a substrate 100 and a doped structure disposed on the back side of the substrate 100.

[0039] The substrate 100 is made of silicon wafer and is used to provide mechanical support for the entire solar cell structure, ensuring the strength and stability of the device; the substrate 100 is also the main region for absorbing sunlight and generating photogenerated carriers.

[0040] The substrate 100 has a front side and a back side along its thickness direction. The front side of the substrate 100 is the light-receiving surface, which is used to absorb light. The back side of the substrate 100 is the non-light-receiving surface, which is used to perform all electrical functions.

[0041] By placing the doped structure on the back side of the substrate 100, the front side of the substrate 100 can receive 100% of the light, which significantly increases the number of photogenerated carriers. At the same time, since there is no limitation on light transmission, the electrodes on the back side of the substrate 100 can be made wider and thicker, thereby significantly reducing the series resistance and laying the foundation for obtaining higher photoelectric conversion efficiency in terms of physical structure.

[0042] The doped structure includes alternating P-type doped pillars 200 and N-type doped pillars 300, indicating that the doped structure is a three-dimensional doped structure formed in the thickness direction of the substrate 100. This transforms the pn junction interface from a two-dimensional plane into a tortuous and enlarged interface in three-dimensional space, providing more and closer paths for charge carriers to be captured and separated by the built-in electric field, significantly improving the charge carrier collection efficiency and thus enhancing the photoelectric conversion efficiency.

[0043] In the doped structure, the doping concentration of the P-type doped pillars 200 and N-type doped pillars 300 is not uniformly distributed, but decreases exponentially along the thickness direction of the substrate 100 to form a gradient energy band.

[0044] Specifically, the doping concentration of the P-type doped pillars 200 and N-type doped pillars 300 decreases exponentially inward along the thickness direction of the substrate 100, starting from the back side of the substrate 100, thereby forming an intrinsic, gradient band structure.

[0045] The gradient band structure ensures a strong, directional driving force along the entire path from the interior of the substrate 100 to the back side, enabling carriers to be efficiently and quickly swept out of the semiconductor bulk region. This greatly reduces the probability of carrier recombination due to prolonged residence time in the bulk and at the contact interface, and significantly suppresses carrier recombination.

[0046] In the thickness direction of substrate 100, both the P-type doped pillar 200 and the N-type doped pillar 300 include opposing tops and bottoms. The tops are far from the back surface of substrate 100 and have a higher doping concentration. When the tops contact the metal electrodes, they ensure the formation of a low-resistance ohmic contact to reduce energy loss. Meanwhile, the bottoms are close to the back surface of substrate 100 and have a lower doping concentration, meaning fewer lattice damage and defects, which is beneficial for achieving high-quality passivation and reducing the surface recombination rate.

[0047] Therefore, the gradient band structure achieves a balance between low contact resistance and high passivation quality, maximizing light absorption and carrier collection efficiency, and resulting in a significant improvement in photoelectric conversion efficiency.

[0048] Continue to refer to Figure 2 Furthermore, the projected area of ​​the bottom in the thickness direction of the substrate 100 is greater than the projected area of ​​the top in the thickness direction of the substrate 100, thereby forming a truncated pyramid-shaped P-type doped pillar 200 and N-type doped pillar 300.

[0049] Among them, the contact point between the top and the metal electrode is one of the most serious carrier recombination points. Reducing the contact area between the top and the metal electrode minimizes the recombination loss in the metal contact area. Increasing the contact area between the bottom and the back of the substrate 100 forms a broad PN junction interface, providing a wider and more convenient collection entrance for carriers generated from various parts of the substrate 100, which significantly improves the carrier collection efficiency.

[0050] It should be noted that the combination of the truncated pyramid-shaped doped pillar and the gradient band structure naturally forms an internal electric field from bottom to top within the doped pillar, effectively guiding and accelerating the collected charge carriers toward the top electrode, further improving the charge carrier collection efficiency.

[0051] In this embodiment, the doping concentration of the doped structure is 1×10⁻⁶. 18 cm -3 ~1×10 20 cm -3 .

[0052] The above concentration range ensures that the P-type doped pillar 200 and N-type doped pillar 300 can form a good ohmic contact with the metal electrode, significantly reducing contact resistance and series loss.

[0053] Meanwhile, the lower limit of this concentration (1×10) 18 cm -3 This concentration is sufficient to create a sufficiently strong built-in electric field within the silicon mass to efficiently separate and collect charge carriers; the upper limit of this concentration (1×10⁻⁶) is... 20 cm -3 The contact resistance is constrained below the critical value that can induce lattice defects and carrier tunneling-induced recombination, ensuring low contact resistance while effectively suppressing recombination losses caused by high doping, thereby synergistically improving the photoelectric conversion efficiency of the battery.

[0054] In this embodiment of the application, an isolation trench 400 is provided between adjacent P-type doped pillars 200 and N-type doped pillars 300, and a dielectric material is provided in the isolation trench 400.

[0055] The isolation trench 400 can physically isolate the P-type doped pillar 200 and the N-type doped pillar 300, completely eliminating the risk of leakage caused by their close proximity and preventing short circuits.

[0056] The dielectric material in the isolation trench 400 can be silicon dioxide, which has good passivation properties. While achieving absolute electrical isolation between the P-type doped pillar 200 and the N-type doped pillar 300 and eliminating lateral leakage, it can transform the inherent high recombination region at the PN junction into a highly passivated and stable interface, thereby significantly reducing the surface recombination rate.

[0057] The width of the isolation groove 400 is ≤5μm, and the depth of the isolation groove 400 is 0.5μm~1μm.

[0058] The width of the isolation trench 400 is ≤5μm. The ultra-narrow isolation trench 400 can ensure that the P-type and N-type doped regions have a sufficiently large carrier collection area while ensuring the feasibility of the photolithography process.

[0059] The isolation trench 400, with a depth of 0.5μm to 1μm, is sufficient to achieve complete physical and electrical isolation between the P-type and N-type regions, fundamentally eliminating the risk of lateral leakage. At the same time, at this precise depth, the dielectric material within the isolation trench 400 can achieve excellent surface passivation of the trench walls.

[0060] In this embodiment, an amorphous silicon carbide layer 500 is also formed on the top of the P-type doped pillar 200 and the N-type doped pillar 300.

[0061] The amorphous silicon carbide layer 500 effectively reduces the interfacial recombination rate on the crystalline silicon surface through a dual mechanism of chemical passivation (utilizing hydrogen atoms to saturate the silicon surface with dangling bonds) and field-effect passivation (repelling minority carriers through a built-in electric field). This directly leads to an increase in carrier lifetime, thereby significantly improving the open-circuit voltage. Simultaneously, the conductivity of the amorphous silicon carbide layer 500 reduces contact resistance, which, together with the high parallel resistance, enhances the fill factor.

[0062] The thickness of the amorphous silicon carbide layer 500 is 20nm~50nm, and the band gap of the amorphous silicon carbide layer 500 is ≥1.8eV.

[0063] When forming an amorphous silicon carbide layer 500 by plasma-enhanced chemical vapor deposition (PECVD) or other processes, a thickness range of 20nm to 50nm can achieve a high-quality, dense and uniform amorphous silicon carbide layer 500; and this thickness range is sufficient to ensure the continuity and passivation effect of the film, while avoiding the introduction of excessively high series resistance due to excessive thickness.

[0064] The wide bandgap of ≥1.8eV provides a high barrier for carrier transport, enhances field-effect passivation, and allows for efficient carrier selective transport through doping, resulting in low interfacial recombination, high open-circuit voltage, and high fill factor.

[0065] In this embodiment of the application, the back-contact crystalline silicon solar cell further includes a double-layer passivation structure 600.

[0066] A dual-layer passivation structure 600 is disposed between the back side of the substrate 100 and the doped structure. The dual-layer passivation structure 600 includes a first passivation layer and a second passivation layer stacked together. The first passivation layer is close to the back side of the substrate 100. The first passivation layer is a silicon oxide layer and the second passivation layer is an aluminum oxide layer.

[0067] The function of the double-layer passivation structure 600 is to suppress the recombination of charge carriers on the back side of the substrate 100, significantly reduce the recombination rate, and increase the open-circuit voltage. At the same time, the double-layer passivation structure 600 can also increase light absorption and increase short-circuit current to achieve high conversion efficiency.

[0068] In the double-layer passivation structure 600, the silicon oxide layer can form a perfect interface with the back side of the substrate 100, and efficiently passivates the saturated dangling bonds through chemical passivation; the aluminum oxide layer covering it passesivates through its strong field effect, preventing minority carriers from reaching the back side interface of the substrate 100; the combination of the two improves the passivation performance.

[0069] The thickness of the first passivation layer can be 10nm~200nm, and the thickness of the second passivation layer can be 10nm~100nm.

[0070] In this embodiment of the application, the back-contact crystalline silicon solar cell further includes: a textured structure 700, which is disposed on the front side of the substrate 100, and the surface of the textured structure 700 away from the substrate 100 includes a plurality of randomly distributed conical, pyramidal, or spherical micron-sized structures.

[0071] The suede structure 700 forms countless random pyramid-shaped, conical, or spherical micro-suede surfaces, causing incident light to undergo multiple reflections and refractions on the surface. This significantly increases the optical path, thereby greatly reducing the reflectivity of sunlight and enhancing the light-harvesting ability, effectively improving the light conversion efficiency.

[0072] This application also provides a method for fabricating a back-contact crystalline silicon solar cell, which includes the following steps:

[0073] Step S1: Provide a substrate 100, and define alternating P-type doped regions and N-type doped regions on the back side of the substrate 100.

[0074] In step S1, defining alternating P-type and N-type doped regions on the back side of the substrate 100 includes:

[0075] Step S11: A silicon oxide layer and an aluminum oxide layer are sequentially formed on the back side of the substrate 100 by atomic layer deposition (ALD) or chemical vapor deposition (CVD) to obtain a double-layer passivation structure 600.

[0076] Step S12: A window is opened on the double-layer passivation structure 600 by laser to obtain multiple alternating P-type windows and N-type windows, thereby defining multiple P-type doped regions and N-type doped regions.

[0077] In step S1, before defining the alternating P-type doped regions and N-type doped regions on the back side of the substrate 100, the following steps are also included:

[0078] Step S10: A textured structure 700 is formed on the front side of the substrate 100 by chemical etching. The surface of the textured structure 700 away from the substrate 100 includes multiple randomly distributed conical, pyramidal, or spherical micron-sized structures.

[0079] Step S2: Based on the P-type doped region and the N-type doped region, alternately spaced P-type doped pillars 200 and N-type doped pillars 300 are formed on the back side of the substrate 100.

[0080] In the thickness direction of the substrate 100, the doping concentration of the P-type doped pillar 200 and the N-type doped pillar 300 decreases exponentially to form a gradient energy band; and both the P-type doped pillar 200 and the N-type doped pillar 300 include a top and a bottom, with the bottom close to the back side of the substrate 100, and the projected area of ​​the bottom in the thickness direction of the substrate 100 is greater than the projected area of ​​the top in the thickness direction of the substrate 100.

[0081] Step S3: Using the gap between adjacent P-type doped pillars 200 and N-type doped pillars 300 as a mask, etch out isolation trenches 400 and place dielectric material in the isolation trenches 400.

[0082] Step S4: Form an amorphous silicon carbide layer 500 on top of the P-type doped pillar 200 and the N-type doped pillar 300.

[0083] The following detailed description of the fabrication method of the back-contact crystalline silicon solar cell provided in this application is illustrated through specific embodiments:

[0084] Example 1:

[0085] This embodiment provides a method for fabricating a back-contact crystalline silicon solar cell, the specific steps of which are as follows:

[0086] 1. Prepare substrate 100 and texturize the front side of substrate 100.

[0087] An N-type Czochralski single-crystal silicon wafer with a resistivity of 1Ω·cm to 3Ω·cm is provided as a substrate 100. The substrate 100 is subjected to standard chemical cleaning to remove surface contaminants and damaged layers. Subsequently, the front side of the substrate 100 is anisotropically etched by chemical etching to form a uniform, micron-scale, pyramid-shaped textured surface structure 700. The textured surface structure 700 can effectively reduce the reflectivity of incident light.

[0088] 2: Deposit a double-layer passivation structure 600 on the back side of substrate 100.

[0089] First, an atomic layer deposition technique is used to deposit a 100 nm thick silicon oxide layer as an interface layer, followed by a 20 nm thick aluminum oxide layer to obtain a double-layer passivation structure 600. The silicon oxide layer provides excellent interfacial chemical passivation, while the aluminum oxide layer provides strong field-effect passivation, effectively suppressing back-side carrier recombination.

[0090] 3: Define the doped region using laser windowing.

[0091] Based on a pre-designed mask pattern, a series of periodic micron-sized windows are obtained by using a laser to open windows on the double-layer passivation structure 600, namely multiple alternating P-type windows and N-type windows, to define multiple P-type doping regions and N-type doping regions; the aperture of the windows is 15μm~25μm, precisely exposing the substrate 100 below for subsequent selective doping.

[0092] 4: Selective boron diffusion forms P-type doped pillars 200

[0093] Selective boron diffusion is performed via chemical vapor deposition, allowing boron atoms to enter the substrate 100 through a P-type window, forming P-type doped pillars 200. The surface boron concentration gradient of the P-type doped pillars 200 is 5 × 10⁻⁶. 19 cm -3 ~2×10 20 cm -3 The gradient layer thickness is 100nm~200nm.

[0094] 5: Phosphorus implantation and laser annealing form N-type doped pillars 300

[0095] Ion implantation technology is used to dope the N-type window with phosphorus (P) as a dopant to form an N-type doped pillar 300. Then, laser annealing is used to selectively scan and anneal the phosphorus implantation region to activate phosphorus atoms and repair lattice damage caused by ion implantation, ensuring that the N-type doped pillar 300 has excellent electrical properties.

[0096] 6: Etching and filling isolation grooves 400

[0097] An isolation trench 400 with a depth of 0.8 μm and a width of 4 μm was etched using an inductively coupled plasma etching process, with the gap between adjacent P-type doped pillars 200 and N-type doped pillars 300 serving as a mask. Silicon dioxide was then filled into the isolation trench 400 using thermal oxidation or plasma-enhanced chemical vapor deposition to form a complete electrical isolation structure.

[0098] 7: Deposition of 500 amorphous silicon carbide layer

[0099] A 30 nm thick amorphous silicon carbide layer 500 is deposited in the interface region between the P-type doped pillar 200 and the N-type doped pillar 300 using plasma-enhanced chemical vapor deposition. The amorphous silicon carbide layer 500 has a wide bandgap of ≥1.8 eV, and its high barrier can effectively suppress the lateral recombination of charge carriers at the interface.

[0100] Through the above steps, a high-efficiency solar cell with a back-side interlaced finger-like back contact structure was successfully fabricated. This structure combines excellent passivation performance and low interfacial recombination characteristics, significantly improving the cell's open-circuit voltage and fill factor.

[0101] In summary, this application provides a back-contact crystalline silicon solar cell, comprising: a substrate 100; and a doped structure disposed on the back side of the substrate 100, wherein the doping concentration of the doped structure decreases exponentially along the thickness direction of the substrate 100 to form a gradient energy band; in the thickness direction of the substrate 100, the doped structure includes a top and a bottom opposite each other, the bottom being close to the back side of the substrate 100, and the projected area of ​​the bottom in the thickness direction of the substrate 100 being greater than the projected area of ​​the top in the thickness direction of the substrate 100; the doped structure includes alternately spaced P-type doped pillars 200 and N-type doped pillars 300.

[0102] By forming alternately spaced P-type doped pillars 200 and N-type doped pillars 300 on the back side of the substrate 100, a three-dimensional doped structure is formed in the thickness direction of the substrate 100. This transforms the pn junction interface from a two-dimensional plane into a tortuous and enlarged interface in three-dimensional space, providing more and closer paths for charge carriers to be captured and separated by the built-in electric field, significantly improving the charge carrier collection efficiency and thus enhancing the photoelectric conversion efficiency.

[0103] Meanwhile, the doping concentrations of the P-type doped pillars 200 and N-type doped pillars 300 decrease exponentially along the thickness direction of the substrate 100 to form a gradient band. The gradient band structure ensures a strong, directional driving force along the entire path from the interior of the substrate 100 to the back side, enabling carriers to be efficiently and quickly swept out of the semiconductor bulk region. This greatly reduces the probability of recombination due to prolonged residence time in the bulk and at the contact interface, and significantly suppresses carrier recombination.

[0104] The tops of the P-type doped pillars 200 and N-type doped pillars 300 are in contact with the metal electrode, and the high doping concentration at the top ensures the formation of a low-resistance ohmic contact to reduce energy loss. The bottoms of the P-type doped pillars 200 and N-type doped pillars 300 have a lower doping concentration, meaning less lattice damage and defects, which is beneficial for achieving high-quality passivation and reducing the surface recombination rate. Therefore, the gradient band structure also achieves a balance between low contact resistance and high passivation quality, maximizing light absorption and carrier collection efficiency, and resulting in a significant improvement in photoelectric conversion efficiency.

[0105] Furthermore, the projected area of ​​the bottom of the P-type doped pillar 200 and the N-type doped pillar 300 in the thickness direction of the substrate is larger than the projected area of ​​the top of the P-type doped pillar 200 and the N-type doped pillar 300 in the thickness direction of the substrate, thus forming a truncated pyramidal shape for the P-type doped pillar 200 and the N-type doped pillar 300. Reducing the contact area between the top and the metal electrode minimizes recombination losses in the metal contact region; increasing the contact area between the bottom and the back surface of the substrate 100 forms a broad PN junction interface, providing a wider and more convenient collection entrance for charge carriers generated from various parts of the substrate 100, significantly improving the charge carrier collection efficiency, thereby enhancing the photoelectric conversion efficiency.

[0106] The various embodiments or embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

[0107] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0108] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "one" can be understood to convey either singular or plural usage.

[0109] It should be readily understood that the terms “on,” “above,” and “on top of” in this disclosure should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on top of something” but also “on top of something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0110] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still 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. Such 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 this application.

Claims

1. A back-contact crystalline silicon solar cell, characterized in that, include: Substrate (100); as well as A doped structure disposed on the back side of the substrate (100) has a doping concentration that decreases exponentially along the thickness direction of the substrate (100) to form a gradient energy band. In the thickness direction of the substrate (100), the doped structure includes an opposing top and bottom, the bottom being close to the back side of the substrate (100), and the projected area of ​​the bottom in the thickness direction of the substrate (100) being greater than the projected area of ​​the top in the thickness direction of the substrate (100). The doped structure includes alternating P-type doped pillars (200) and N-type doped pillars (300).

2. The back-contact crystalline silicon solar cell according to claim 1, characterized in that, An isolation trench (400) is provided between adjacent P-type doped pillars (200) and N-type doped pillars (300), and a dielectric material is provided in the isolation trench (400).

3. The back-contact crystalline silicon solar cell according to claim 1, characterized in that, An amorphous silicon carbide layer (500) is also formed on the top.

4. The back-contact crystalline silicon solar cell according to claim 1, characterized in that, The back-contact crystalline silicon solar cell further includes: a double-layer passivation structure (600). The double-layer passivation structure (600) is disposed between the back side of the substrate (100) and the doped structure. The double-layer passivation structure (600) includes a first passivation layer and a second passivation layer stacked together. The first passivation layer is close to the back side of the substrate (100). The first passivation layer is a silicon oxide layer, and the second passivation layer is an aluminum oxide layer.

5. The back-contact crystalline silicon solar cell according to claim 1, characterized in that, The back-contact crystalline silicon solar cell further includes: a textured surface structure (700). The textured structure (700) is disposed on the front side of the substrate (100), and the surface of the textured structure (700) away from the substrate (100) includes a plurality of randomly distributed conical, pyramidal or spherical micron-sized structures.

6. The back-contact crystalline silicon solar cell according to claim 2, characterized in that, The width of the isolation groove (400) is ≤5μm; The depth of the isolation groove (400) is 0.5μm~1μm.

7. The back-contact crystalline silicon solar cell according to claim 3, characterized in that, The thickness of the amorphous silicon carbide layer (500) is 20nm~50nm; The bandgap of the amorphous silicon carbide layer (500) is ≥1.8 eV.

8. The back-contact crystalline silicon solar cell according to claim 1, characterized in that, The doping concentration of the doped structure includes 1×10⁻⁶. 18 cm -3 ~1×10 20 cm -3 .

9. A method for fabricating a back-contact crystalline silicon solar cell, used to fabricate the back-contact crystalline silicon solar cell according to any one of claims 1-8, characterized in that, include: A substrate (100) is provided, and alternating P-type doped regions and N-type doped regions are defined on the back side of the substrate (100); Based on the P-type doped region and the N-type doped region, alternating P-type doped pillars (200) and N-type doped pillars (300) are formed on the back side of the substrate (100). In the thickness direction of the substrate (100), the doping concentration of the P-type doped pillars (200) and the N-type doped pillars (300) decreases exponentially to form a gradient energy band. Both the P-type doped pillars (200) and the N-type doped pillars (300) include opposing tops and bottoms. The bottoms are close to the back side of the substrate (100), and the projected area of ​​the bottoms in the thickness direction of the substrate (100) is greater than the projected area of ​​the tops in the thickness direction of the substrate (100).

10. The method for fabricating a back-contact crystalline silicon solar cell according to claim 9, characterized in that, Alternating P-type and N-type doped regions are defined on the back side of the substrate (100), including: A silicon oxide layer and an aluminum oxide layer are sequentially formed on the back side of the substrate (100) to obtain a double-layer passivation structure (600). By using a laser to create windows in the double-layer passivation structure (600), alternating P-type and N-type windows are obtained to define the P-type doped region and the N-type doped region.

11. The method for fabricating a back-contact crystalline silicon solar cell according to claim 9, characterized in that, After forming alternately spaced P-type doped pillars (200) and N-type doped pillars (300) on the back side of the substrate (100), the method further includes: Using the gap between adjacent P-type doped pillars (200) and N-type doped pillars (300) as a mask, an isolation trench (400) is etched out. Dielectric material is disposed within the isolation groove (400).

12. The method for fabricating a back-contact crystalline silicon solar cell according to claim 11, characterized in that, After the dielectric material is placed in the isolation groove (400), the method further includes: An amorphous silicon carbide layer (500) is formed on the top of the P-type doped pillar (200) and the N-type doped pillar (300).

13. The method for fabricating a back-contact crystalline silicon solar cell according to claim 9, characterized in that, Before defining alternating P-type and N-type doped regions on the back side of the substrate (100), the method further includes: A textured structure (700) is formed on the front side of the substrate (100) by a chemical etching method. The surface of the textured structure (700) away from the substrate (100) includes a plurality of randomly distributed conical, pyramidal, or spherical micron-sized structures.

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