Study on nano-pores enlargement during Ag-assisted electroless etching of diamond wire sawn polycrystalline silicon wafers

In this paper, diamond wire sawn (DWS) mc-Si wafers were textured using Ag-assisted electroless etching (AgNO₃+HF+H₂O₂) combined with an auxiliary etching (HF+HNO₃). The evolution mechanism of the surface texture structure on the wafers was investigated in detail. It was noted that during the AgNO₃+HF+H₂O₂ etching, there existed the difference in the axial direction and the depth of nano-pores among different grains. This difference made the different grains form different texture structures during the following HF+HNO₃ etching. Since the etching of poly-silicon is isotropic in HF+HNO₃ solution, it was the AgNO₃+HF+H₂O₂ etching rather than the auxiliary etching (HF+HNO₃) that resulted in the different texture structure among different grains. During the HF+HNO₃ etching, the diameter of the etched pits on the wafer surface was enlarged quickly through the adjacent pits combination. The depth of the etched pits hardly increased because the top and bottom of pits were etched at the same time. As a result, the ratio of depth to diameter of the pits decreased. The texture difference among the grains and decrease of the ratio of depth to diameter of the pits limited the further enhancement of the PV efficiency of mc-Si solar cell. Therefore, the improving the uniformity of AgNO₃+HF+H₂O₂ etching for the different crystal orientation grains and obtaining a large ratio of depth to diameter of the pits during the HF+HNO₃ etching are two critical issues to enhance the PV efficiency of mc-Si solar cell.