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EP-4391091-B1 - METHOD FOR MANUFACTURING A SOLAR CELL

EP4391091B1EP 4391091 B1EP4391091 B1EP 4391091B1EP-4391091-B1

Inventors

  • FANG, Mingliang
  • HOU, KUN
  • LIU, Zonggang
  • MA, Lie

Dates

Publication Date
20260513
Application Date
20230922

Claims (11)

  1. A method for preparing a solar cell, the preparation method comprising: performing a texturing process and a boron or phosphorus diffusion process sequentially, wherein the preparation method further comprises, between the texturing process and the boron or phosphorus diffusion process: heating a silicon wafer (10), that has been wet-textured loaded in a wafer cassette, to form a first oxide layer (30) on both front and back sides of the silicon wafer (10) to absorb impurities in the silicon wafer (10); and removing the first oxide layer on the front and back sides of the silicon wafer (10); characterized in that the heating method comprises: heating the textured silicon wafer (10) in a pure oxygen environment to a first preset temperature, and preserving the temperature for a first preset time; wherein the first preset temperature is within a range of 600°C to 800°C, and the first preset time is within a range of 30s to 60s.
  2. The method for preparing the solar cell according to claim 1, wherein a thickness of the first oxide layer (30) is within a range of 4 nm to 5 nm.
  3. The method for preparing the solar cell according to claim 1, wherein the silicon wafer (10) is an n-type monocrystalline silicon wafer, and the solar cell comprises a passivation/anti-reflection film, a passivation layer, a p-type emitter, an n-type monocrystalline silicon wafer substrate, a tunneling oxide layer, an n-type polysilicon film, and an anti-reflection film that are stacked.
  4. The method for preparing the solar cell according to claim 1, wherein the first preset temperature is within a range of 700°C to 800°C.
  5. The method for preparing the solar cell according to claim 1, wherein the method of removing the first oxide layer (30) on the front and back sides of the silicon wafer (10) comprises: cleaning the silicon wafer (10) using a cleaning agent, wherein a cleaning time is within a range of 30s to 50s, and the cleaning agent comprises HF.
  6. The method for preparing the solar cell according to claim 5, wherein the cleaning agent comprises the HF with a volume concentration of 15% to 30%.
  7. The method for preparing the solar cell according to claim 6, wherein the cleaning agent further comprises HCl.
  8. The method for preparing the solar cell according to claim 7, wherein the cleaning agent further comprises the HCl with a volume concentration of 5% to 10%.
  9. The method for preparing the solar cell according to claim 7, wherein the cleaning agent comprises the HF and the HCl with a volume ratio of 3:1.
  10. The method for preparing the solar cell according to claim 5, wherein after the cleaning the silicon wafer (10) using the cleaning agent, a second oxide layer is formed on a surface of the silicon wafer (10), and the boron or phosphorus diffusion process is performed on the silicon wafer (10) formed with the second oxide layer on a surface thereof.
  11. The method for preparing the solar cell according to claim 10, wherein the method of forming the second oxide layer comprises: purging the silicon wafer with ozone.

Description

TECHNICAL FIELD The present disclosure relates to the technical field of solar cells, and specifically, to a method for manufacturing a solar cell. BACKGROUND Currently on the market, most tunnel oxide passivated contact (TOPCon) cells are based on P-type monocrystalline silicon. However, the photoelectric conversion efficiency of the P-type TOPCon cells is difficult to reach above 23.5%, and the efficiency in the industry is currently close to the limit. Cells based on N-type silicon have higher conversion efficiency. Developing and producing N-type high-efficiency cells is an effective way to improve the photoelectric conversion efficiency. For N-TOPCon cells, the current mainstream preparation process includes: silicon wafer - texturing - boron diffusion - backside etching - tunneling oxidation - in-situ doped amorphous silicon - wraparound plating - front side aluminum oxide - front side silicon nitride - back side silicon nitride - printing and sintering - testing and sorting. However, the inventors found that TOPCon cells prepared using traditional preparation process often turned black during an electro luminescence (EL) test. Moreover, the prepared TOPCon cells are prone to problems such as blackening and low efficiency. Lozac'h Mickael et al: "Role of silicon surface, polished 〈100〉 and (111) or textured, on the efficiency of double-sided TOPCon solar cells"; Progress in Photovoltaics: Research and Applications, Vol. 28, No. 10, 25 June 2020, pages 1001-1011, XP055916906 discusses the role of the silicon surface and orientation on double-sided TOPCon solar cells properties. The solar cells of front and rear, (p) and (n), poly-Si/SiOx stack, fabricated on polished surfaces oriented 〈100〉 and (111) and pyramid textured surfaces, are characterized as a function of the thickness of an ultrathin SiOx layer, controlled at atomic scale from one- to four-cycle atomic layer deposition (ALD). It is stated therein that the optimized thickness of the ultrathin SiOx is about 1.1 ± 0.1 nm, corresponding to a two-cycle ALD, regardless of the surface and orientation of the c-Si substrate. The open-circuit voltage is about 10 mV higher on the polished (100) -oriented surface, associated with lower defect density at the interface of SiOx/c-Si. On the other hand, the contact resistance is much lower, about 0.45 Ω /cm2, on the polished (111) - oriented surface. On textured surfaces, a photoconversion efficiency of 19.1% is demonstrated for the double-sided TOPCon structure strictly for a SiOx thickness with two-cycle ALD. SUMMARY Based on the above-mentioned shortcomings, the present application provides a method for manufacturing a solar cell, to partially or fully improve or even solve the problem of blackening of solar cells in related arts. This application is implemented as follows: In a first aspect, an embodiment of the present application provides a method for preparing a solar cell. The preparation method includes: performing a texturing process and a boron or phosphorus diffusion process sequentially. Between the texturing process and the boron or phosphorus diffusion process, the preparation method further includes: heating a silicon wafer that has been wet-textured loaded in a wafer cassette to form a first oxide layer on both front and back sides of the silicon wafer to absorb impurities in the silicon wafer; and removing the first oxide layer on the front and back sides of the silicon wafer; wherein the heating method comprises: heating the textured silicon wafer (10) in a pure oxygen environment to a first preset temperature, and preserving the temperature for a first preset time; wherein the first preset temperature is within a range of 600°C to 800°C, and the first preset time is within a range of 30s to 60s. Optionally, a thickness of the first oxide layer is within a range of 4 nm to 5 nm. During the above implementation, after using the wafer cassette to load the wet-textured silicon wafer, some impurities such as additives and alkali crystals will inevitably remain at the contact area between the silicon wafer and the teeth position of the wafer cassette, so there will be defects at the contact position between the silicon wafer and the wafer cassette. After wet texturing the silicon wafer loaded in the wafer cassette, the silicon wafer is heated to form the first oxide layer on the front and back sides of the silicon wafer to absorb the impurities such as organic matter and alkali crystals attached to the surface of the silicon wafer. Then, the first oxide layer adsorbed with the impurities is removed, which can improve the cleanliness of the surface of the silicon wafer, thereby further improving the uniformity of the subsequent boron diffusion or phosphorus diffusion process, and improving the quality and efficiency of the solar cell. If the subsequent boron diffusion or phosphorus diffusion process is directly performed on the textured cell, the defects at the contact position between the sili