A back contact crystalline silicon solar cell suppressing resonance absorption and a method for manufacturing the same

Abstract

The application discloses a back contact crystalline silicon solar cell for inhibiting resonance absorption and a preparation method thereof, and belongs to the field of solar cells. The back contact crystalline silicon solar cell comprises a silicon substrate, a transparent conductive oxide layer located at the back of the silicon substrate, and a metal electrode located on the transparent conductive oxide layer, and a dielectric layer is introduced between the transparent conductive oxide layer and the metal electrode; the dielectric layer is arranged as an optical isolation layer, destroys the excitation condition of surface plasmon at the interface of the transparent conductive oxide layer and the metal electrode, so as to inhibit the parasitic absorption of light energy; meanwhile, the photo-generated carriers are allowed to be transmitted to the metal electrode through the quantum tunneling effect. The application can significantly improve the short-circuit current density and conversion efficiency of the cell, has good process compatibility and controllable cost, and is suitable for the mass production preparation of various back contact crystalline silicon solar cells such as HTBC and HBC.

Description

Technical Field

[0001] This invention belongs to the field of solar cells, and in particular relates to a back-contact crystalline silicon solar cell that suppresses resonant absorption and its preparation method. Background Technology

[0002] Unlike conventional cell structures, back contact (BC) crystalline silicon solar cells have their positive and negative electrodes arranged in an interdigitated pattern on the back of the cell, which can demonstrate significant technological advantages: (1) The elimination of the front grid lines can achieve zero light shading and zero reflection loss, effectively improving the short-circuit current density of the cell; (2) By introducing multi-step laser film-opening technology, the passivation performance of the back passivation layer is protected, which can reduce carrier recombination loss at the interface and improve photoelectric conversion efficiency; (3) Compared with traditional crystalline silicon photovoltaic cells, BC cells have a more aesthetically pleasing appearance; (4) As a platform technology, the BC route can be combined with various technical routes such as tunneling oxide passivation contact (TOPCon) and silicon heterojunction (SHJ) to form more efficient tunneling oxide back contact (TBC), back contact heterojunction solar cells (HBC), and heterojunction tunneling oxide back contact solar cells (HTBC). In particular, the HTBC battery integrates the key technological advantages of SHJ's TOPCon battery to form a high-efficiency HTBC battery, which has continuously broken the conversion efficiency record of single-cell crystalline silicon solar cells, reaching 28.13%, which is infinitely close to the Shockley-Quyther theoretical limit (about 29.4%), and is recognized by the industry as the mainstream technology direction for the next generation of high-efficiency crystalline silicon cells.

[0003] With the continuous advancement of cost reduction and efficiency improvement in the photovoltaic industry, thinner silicon wafers have become a clear technological trend. Currently, the thickness of silicon wafers for mainstream back-contact solar cells (especially HTBCs) is generally below 150 μm, and is trending towards 130 μm, 110 μm, or even thinner wafers. While thinner silicon wafers reduce material costs, they also allow more long-wavelength light to penetrate the silicon substrate and reach the interface between the transparent conductive oxide (TCO) and the metal electrode on the back side, exciting surface plasmon resonance absorption. Specifically, the energy of photons excites free electrons at the TCO-metal interface to oscillate collectively, forming surface plasmon polaritons. As these polaritons propagate along the interface, their energy is rapidly dissipated within the metal and converted into heat, resulting in parasitic absorption of this portion of light energy, which cannot be effectively utilized by the cell, ultimately causing a significant decrease in current density. Compared to traditional high-efficiency cells, BC cells have both positive and negative electrodes arranged on the back side, increasing the TCO-metal interface area by at least 50% or even more, making the impact of this resonance absorption effect on cell performance particularly pronounced. Furthermore, the effective transmittance of the TCO film itself still has room for improvement, further exacerbating the loss of long-wavelength light. The combination of these multiple factors ultimately leads to a significant decrease in the battery's short-circuit current density, thus limiting further improvements in the BC battery's conversion efficiency.

[0004] Currently, no effective solution has been found for the resonance absorption problem at the TCO-metal interface in BC batteries, which is highlighted by silicon wafer thinning. Existing technologies mainly focus on optimizing the BC battery fabrication process to reduce costs or improving the performance of the TCO film itself to reduce optical losses, but fail to address the resonance absorption between the TCO and metal electrodes from the perspective of interface physics mechanisms. Therefore, there is an urgent need for a method or structure that can physically suppress the resonance absorption at the TCO-metal interface in BC batteries, in order to further overcome the optical loss bottleneck of BC batteries and improve their photoelectric conversion efficiency. Summary of the Invention

[0005] To address the resonant absorption problem at the TCO-metal interface in BC solar cells, which is exacerbated by silicon wafer thinning, existing technologies primarily focus on optimizing the BC cell fabrication process to reduce costs or improving the performance of the TCO film itself to reduce optical losses. However, they fail to address the resonant absorption between the TCO and metal electrodes from the perspective of interface physics mechanisms. This invention provides a back-contact crystalline silicon solar cell with resonant absorption suppression and its fabrication method. By introducing a dielectric layer between the TCO layer and the metal electrode as an optical isolation layer, the excitation conditions of surface plasmon resonances are physically disrupted, effectively suppressing resonant absorption. Simultaneously, photogenerated carriers are transported to the metal electrode via quantum tunneling without sacrificing electrical contact. Furthermore, the dielectric layer is systematically matched and optimized with TCO films of different thicknesses to construct a synergistic "TCO-dielectric layer-metal" composite back-reflective film stack, aiming to minimize optical parasitic absorption while achieving optimal carrier collection efficiency.

[0006] Based on the above technical objectives, the embodiment provides a back-contact crystalline silicon solar cell that suppresses resonant absorption. The back-contact crystalline silicon solar cell includes a silicon substrate, a transparent conductive oxide layer located on the back side of the silicon substrate, and a metal electrode located on the transparent conductive oxide layer; and a dielectric layer is introduced between the transparent conductive oxide layer and the metal electrode. The dielectric layer is configured as an optical isolation layer to disrupt the excitation conditions of surface plasmon polaritons at the interface between the transparent conductive oxide layer and the metal electrode, thereby suppressing parasitic absorption of light energy; at the same time, it allows photogenerated carriers to be transported to the metal electrode through the quantum tunneling effect.

[0007] Preferably, the thickness of the dielectric layer is 0.1 nm to 10 nm.

[0008] Preferably, the dielectric layer is made of Al2O3, SiO2, or MgF2. x LiF x One or more of polymethyl methacrylate (PMMA) and methyl [6,6]-phenyl-C61-butyrate (PCBM).

[0009] More preferably, the dielectric layer is made of Al2O3, SiO2, or MgF2. x LiF x One or more of them.

[0010] Choosing a dielectric material with low refractive index and high transparency to construct the dielectric layer can effectively suppress resonant absorption while ensuring that photogenerated carriers are transported to the metal electrode through quantum tunneling without sacrificing electrical contact. Any dielectric material with low refractive index and high transparency is within the scope of protection of this application.

[0011] Preferably, the back-contact crystalline silicon solar cell is an HTBC cell or an HBC cell, the back side of which includes an N region, a P region, and a gap region located between the N region and the P region, and the dielectric layer also covers the surface of the p-type amorphous silicon thin film exposed in the gap region.

[0012] This dielectric layer covers the exposed Pa-Si:H film surface in the gap region of the HTBC, preventing damage to the Pa-Si:H film from chemical etching solutions during subsequent processes. It also improves the environmental stability of the battery.

[0013] Preferably, the thickness of the silicon substrate does not exceed 200 μm.

[0014] Preferably, the transparent conductive oxide layer is selected from one or more of the following systems: The first system is an indium oxide-based material, which includes one or more of indium tin oxide, indium titanium oxide, indium zinc oxide, and indium tungsten oxide, and the light transmittance of the indium oxide-based material is not less than 85%, and the sheet resistance is 50~200 Ω / sq; The second system is a tin oxide-based material, which includes fluorine-doped tin oxide or antimony-doped tin oxide; The third system is a zinc oxide-based material, which includes aluminum-doped zinc oxide or gallium-doped zinc oxide. The fourth system is a multi-component oxide material, which includes indium zinc oxide or indium gallium zinc oxide; The fifth system is a titanium dioxide-based material, which includes niobium-doped titanium dioxide.

[0015] More preferably, the thickness of the transparent conductive oxide layer is 10~100 nm.

[0016] By systematically matching and optimizing the polarity of the transparent conductive oxide layer and dielectric layer within the aforementioned thickness range, a synergistic composite back-reflection film stack of transparent conductive oxide layer-dielectric layer-metal is constructed to achieve optimal carrier collection efficiency while minimizing optical parasitic absorption.

[0017] More preferably, the thickness of the transparent conductive oxide layer is 40~80 nm.

[0018] On the other hand, the present invention also provides a method for fabricating the back-contact crystalline silicon solar cell that suppresses resonant absorption, comprising: providing a silicon substrate, and sequentially depositing a transparent conductive oxide layer, a dielectric layer and a metal electrode on the back side of the silicon substrate.

[0019] The silicon substrate is a semi-finished battery without the deposition of a transparent conductive layer and subsequent films. On the other hand, the present invention also provides a photovoltaic module, the structure of which includes the back-contact crystalline silicon solar cell for suppressing resonant absorption.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention specifically sets an ultrathin dielectric layer between the TCO layer and the metal electrode. As an optical isolation layer, the dielectric layer physically destroys the excitation conditions of surface plasmon polaritons, effectively suppresses the parasitic absorption of light energy at the TCO-metal interface, and enables the battery to effectively utilize the long-wavelength light that would otherwise be wasted.

[0021] (2) The present invention precisely controls the thickness of the ultrathin dielectric layer. This thickness window simultaneously meets the dual requirements of optical isolation and electrical tunneling: ensuring that an effective physical isolation layer is formed between the TCO and the metal, fully suppressing the excitation of surface plasmon polaritons; ensuring that photogenerated carriers can be efficiently transmitted to the metal electrode through the quantum tunneling effect, without affecting the fill factor due to the increase in series resistance.

[0022] (3) The present invention also systematically matches and optimizes the ultrathin dielectric layer with TCO layers of different thicknesses to form a TCO-dielectric layer-metal composite back reflection film stack. Through the synergistic configuration of the TCO layer thickness and the dielectric layer thickness, a better back reflection effect is achieved in the long wavelength band, further increasing the optical path of light in the silicon substrate and improving the absorption rate of the silicon substrate for long wavelength photons.

[0023] (4) The ultrathin dielectric layer of the present invention can also cover the surface of the exposed p-type amorphous silicon film in the gap region of HBC or HTBC batteries to prevent the chemical etching solution from damaging the p-type amorphous silicon film in subsequent processes. At the same time, the dielectric layer can act as a diffusion barrier layer to effectively prevent copper atoms in the metal electrode from diffusing into the battery to form deep energy recombination centers, and can also block moisture intrusion, thereby improving the long-term reliability of the battery. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a back-contact crystalline silicon solar cell provided in an embodiment of the present invention.

[0025] Figure 2 Absorption curves of silicon substrates with different dielectric layers provided in the embodiments, wherein the inset is an enlarged view of the absorption curves in the wavelength range of 450~1100 nm.

[0026] Figure 3 Absorption curves of silicon substrates with different dielectric layers and TCO film stacks provided for the embodiments, wherein the inset is an enlarged view of the absorption curves in the wavelength range of 450~1100 nm. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0028] Example 1 In the embodiments, the method for fabricating a back-contact crystalline silicon solar cell that suppresses resonant absorption includes the following steps: providing a silicon substrate, and sequentially depositing a transparent conductive oxide layer, a dielectric layer and a metal electrode on the back side of the silicon substrate to obtain a back-contact crystalline silicon solar cell.

[0029] Taking HTBC batteries as an example, this technology is not limited to this one battery structure; it is also applicable to HBC batteries. The HTBC battery structure is as follows: Figure 1 As shown, three regions are circled: the N-region for collecting electrons, the P-region for collecting holes, and the gap region to isolate the N-region from the P-region, preventing short circuits and leakage caused by direct contact between N and P. The specific preparation method is as follows: (1) Silicon wafer preparation: Provide an N-type single crystal silicon substrate with a thickness of 200 μm, and clean and polish the silicon wafer to form a flat polished surface.

[0030] (2) Preparation of tunneling oxygen SiO2 and n-poly: Tunneling oxygen and n-poly layers are deposited on the back side of the silicon wafer by low-pressure chemical vapor deposition. The thickness of tunneling oxygen is 0.1~2 nm and the thickness of n-poly is 70~200 nm.

[0031] (3) Using laser ablation technology, a P-region is formed by creating openings in SiO2 / n-poly. The laser used is green picosecond or nanosecond, and the width of the P-region is 200~500 μm. Note: The SiO2 / n-poly is directly removed by laser.

[0032] (4) Use wet cleaning to remove laser residue from the P area after laser drilling, and then use an alkaline solution to form a uniform pyramid shape on the back P area and the front surface.

[0033] (5) Preparation of front passivation and antireflection layer: An aluminum oxide passivation layer with a thickness of 5~15 nm is deposited on the front side of the silicon wafer using atomic layer deposition. Then, silicon nitride or silicon oxide or its stacked antireflection layer is deposited on the aluminum oxide layer using plasma-enhanced chemical vapor deposition, with a total thickness of 60~150 nm.

[0034] (6) Backside p-region preparation: Intrinsic amorphous silicon (ia-Si:H) and p-type amorphous silicon thin film (pa-Si:H) or p-type microcrystalline silicon are deposited on the textured p-region pyramid in (4) by plasma-enhanced chemical vapor deposition. At this time, intrinsic amorphous silicon and p-type amorphous silicon thin film are also deposited on SiO2 / n-poly. The thickness of the i-layer is 5~20 nm and the thickness of the p-layer is 10~40 nm.

[0035] (7) Using laser ablation technology, N-regions are formed by creating openings in SiO2 / n-poly / ia-Si:H / pa-Si:H. The laser used is green picosecond or nanosecond, and the width of the N-region is 100~300 μm. Note: The ia-Si:H / pa-Si:H is directly removed by laser, leaving SiO2 / n-poly as the N-region. The area where the laser did not act is used to form the gap region later.

[0036] (8) Wet cleaning of residues left after laser treatment.

[0037] (9) Deposition of transparent conductive oxide layer: A transparent conductive oxide layer (TCO layer) is deposited on the entire back side of the battery using reactive plasma deposition (RPD). The material is selected from indium oxide-based materials, specifically tungsten-doped indium oxide thin film (IWO) with a thickness of 50 nm. (10) Use laser or etching paste to etch away the TCO above the gap to form the isolation gap area, thus avoiding short circuit between the N area and the P area.

[0038] (11) Deposition of an ultrathin dielectric layer: An ultrathin dielectric layer is deposited on the TCO layer. The dielectric material is MgF2, the deposition method is physical vapor deposition, and the deposition thickness is 10 nm. The ultrathin dielectric layer completely covers the surface of the TCO layer, resulting in a dielectric layer 3 / TCO film.

[0039] (12) Metal electrode preparation: A metal Cu electrode layer with a thickness of 8~30 μm is deposited on the ultrathin dielectric layer by screen printing.

[0040] (13) The ultrathin dielectric layer above the gap does not need to be removed, serving as a natural protective barrier.

[0041] Example 2 The process of Example 2 is the same as that of Example 1, except that the thickness of the dielectric layer is 1 nm, resulting in a dielectric layer 1 / TCO thin film.

[0042] Example 3 The process of Example 3 is the same as that of Example 1, except that the thickness of the dielectric layer is 5 nm, resulting in a dielectric layer 2 / TCO thin film.

[0043] Example 4 The process in Example 4 is the same as in Example 1, except that the thickness of the transparent conductive oxide layer is 10 nm, resulting in a dielectric layer / TCO-1 thin film.

[0044] Example 5 The process of Example 5 is the same as that of Example 1, except that the thickness of the transparent conductive oxide layer is 30 nm, and a dielectric layer / TCO-2 thin film is obtained.

[0045] Comparative Example 1 The process of Comparative Example 1 is the same as that of Example 1, except that: no ultrathin dielectric layer deposition is performed, resulting in a dielectric-free / TCO thin film.

[0046] Detection Example 1 Absorption tests were performed on the thin films prepared in the examples and comparative examples. The results are as follows: Figure 2 As shown, experimental results demonstrate that introducing an ultrathin dielectric layer material can enhance the absorption of the silicon substrate in the visible light band, thereby generating more photogenerated carriers and increasing the short-circuit current density. These data prove that the resonant absorption between the TCO and the metal electrode proposed in this invention can be significantly reduced by introducing a dielectric layer.

[0047] Simultaneously, TCO thin films of different thicknesses were matched and optimized to form a TCO-dielectric layer-metal composite back reflective film stack, such as... Figure 3 As shown, the experimental results indicate that the light absorption of the silicon substrate can be further increased, thereby improving the spectral utilization rate.

[0048] Furthermore, the battery prepared in Example 1 can effectively prevent the entry of moisture during stability testing and can prevent organic matter in Cu or Cu slurry from diffusing from the Gap region into the battery interior to form deep-level recombination centers.

[0049] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A back-contact crystalline silicon solar cell for suppressing resonant absorption, characterized in that, The back-contact crystalline silicon solar cell includes a silicon substrate, a transparent conductive oxide layer located on the back side of the silicon substrate, and a metal electrode located on the transparent conductive oxide layer, with a dielectric layer introduced between the transparent conductive oxide layer and the metal electrode. The dielectric layer is configured as an optical isolation layer to disrupt the excitation conditions of surface plasmon polaritons at the interface between the transparent conductive oxide layer and the metal electrode, thereby suppressing parasitic absorption of light energy; at the same time, it allows photogenerated carriers to be transported to the metal electrode through the quantum tunneling effect.

2. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 1, characterized in that, The thickness of the dielectric layer is 0.1~10 nm.

3. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 2, characterized in that, The dielectric layer is made of Al2O3, SiO2, or MgF2. x LiF x One or more of polymethyl methacrylate and [6,6]-phenyl-C61-butyrate.

4. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 1, characterized in that, The back-contact crystalline silicon solar cell is an HTBC cell or an HBC cell. The back side of the HTBC cell or HBC cell includes an N region, a P region, and a gap region located between the N region and the P region. The dielectric layer also covers the surface of the p-type amorphous silicon thin film exposed in the gap region.

5. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 1, characterized in that, The thickness of the silicon substrate is no more than 200 μm.

6. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 1, characterized in that, The transparent conductive oxide layer is selected from one or more of the following systems: The first system is an indium oxide-based material, which includes one or more of indium tin oxide, indium titanium oxide, indium zinc oxide, and indium tungsten oxide, and the light transmittance of the indium oxide-based material is not less than 85%, and the sheet resistance is 50~200 Ω / sq; The second system is a tin oxide-based material, which includes fluorine-doped tin oxide or antimony-doped tin oxide; The third system is a zinc oxide-based material, which includes aluminum-doped zinc oxide or gallium-doped zinc oxide. The fourth system is a multi-component oxide material, which includes indium zinc oxide or indium gallium zinc oxide; The fifth system is a titanium dioxide-based material, which includes niobium-doped titanium dioxide.

7. The back-contact crystalline silicon solar cell for suppressing resonant absorption according to claim 6, characterized in that, The thickness of the transparent conductive oxide layer is 10~100 nm.

8. The method for preparing a back-contact crystalline silicon solar cell with suppressed resonant absorption according to any one of claims 1 to 7, characterized in that, include: A silicon substrate is provided, and a transparent conductive oxide layer, a dielectric layer and a metal electrode are sequentially deposited on the back side of the silicon substrate to obtain a back-contact crystalline silicon solar cell.

9. A photovoltaic module, characterized in that, The structure includes the back-contact crystalline silicon solar cell for suppressing resonant absorption as described in any one of claims 1 to 7.

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