Investigation On Fabrication Of Composite Texture And Wettability For Multicrystalline Silicon Solar Cell

Black silicon is a novel material with strongly light trapping nanostructure and having extremely low reflectance in visible light. In recent years, the use of its low reflection performance has attracted great attention of the researchers in crystalline silicon solar cell industry at home and abroad. Among many methods to fabricate the black silicon nanostructures, metal assisted chemical etching (MACE) showed remarkable advantages such as simple equipment, low cost, and is easy to realize the industrialization production. In this paper, the MACE was used to fabricate the nanostructure on multicrystalline silicon wafers surface which textured by the traditional acid method. Then the anti-reflection properties and optic-electronic properties and wettability of the composite structures were studied.In this paper, to decrease the reflectance of silicon wafer, one-step MACE and two-steps MACE were used for fabricating the nanostructure texture on the traditional acid textured multicrystalline silicon wafer. The reflectance of micro-nano composite textured silicon, which is fabricated by two-steps MACE, is below 5%. The Tetramethylammonium Hydroxide (TMAH) solution was used to modify the micro-nano composite texture. The surface reflectance increased as the increase of TMAH modified time. After the process optimization, the average photoelectric conversion efficiency improved by 0.13%.The mixed acid solution (HNO3-HF solution) was used for modifying the micro-nano composite texture. It was found that the nanopores of the silicon surface combined into submicron pores. On account of the etching speed of horizontal is larger than the etching speed of vertical, the depth-diameter ratio of pores would reduce gradually. The SiO2 layer was fabricated by O3 passivation before Plasma Enhanced Chemical Vapor Deposition (PECVD) coating. The Si-SiO2-SiNx stacks could improve the photoelectric conversion efficiency effectively. Control the sheet resistance at 90/□ by adjusting the process of P diffusion also could improve the photoelectric conversion efficiency effectively. The average photoelectric conversion efficiency of composite textured silicon solar cells was improved by 0.36%.In the point of the basic issue of surface etching, the silicon surface wettability was characterized by the surface contact angle, to solve the problem that the low depth-diameter ratio of micro-submicron pores. The relationship between wettability and surface structures and crystal plain were studied respectively. The etching behavior of the micro-nano structures top and bottom were discussed. The smaller the structure scales, the smaller the surface water contact angles are. Different crystal plains have different contact angle due to their different surface energy. Gas babbles were easily absorbed on the silicon surface when it was etching by H2O2-HF solution and TMAH solution. The nonionic surfactant (Tween Series) was used for improving the wettability between silicon wafer and water. The micro-submicron composite texture with large amount of deeper pores were fabricated by AgNO3-HF solution with Tween-80.