RIE texturing optimization for thin c-Si solar cells in SF₆/O₂plasma

Abstract

Dry etching plasma parameters were optimized for texturing single crystalline thin silicon solar cells and hence for high efficiency. In reactive ion etching (RIE) texturing, a low etch depth (∼2 µm) was obtained compared with the etch depth that occurred in the wet chemical texturing process. For the flow ratios (SF6/O2) of 2 and 3, needle-like and cylindrical type structured surfaces were obtained. In the RIE process, the effects of working pressure, flow ratio, and etching time on reflectance and electrical properties of single crystalline silicon solar cells were investigated. The textured c-Si wafer with needle-like structure has good antireflectance behaviour. The interface defect density (Dit) in these textured silicon wafers increased with etching time. But an improvement in the reduction of interface trap density was observed through the annealing effect. Single crystalline solar cells with cylindrical type texture have higher values for open circuit voltage, short circuit current and efficiency in spite of a higher reflectance as compared with those needle-like structures. It is observed that the optimized SF6/O2 based chemistry in the RIE method is more suitable for thin crystalline silicon solar cells instead of the conventional wet texturization processes.