Optimization of roughness, reflectance and photoluminescence for acid textured mc-Si solar cells etched at different HF/HNO3 concentrations

The surface structure of multi-crystalline silicon (mc-Si) etched in HF/HNO3 at different HF/HNO3 concentrations is optimized for being applied in solar cells. The resulting texture, which determines the efficiency of solar cells, was characterized by means of scanning electron microscopy (SEM) and optical spectroscopy. The roughness of the surface increases and the reflectance decreases when the content of HNO3 in the etching solution is increased to a limit. The produced etched pits on the surface have been identified by SEM and the surface mean roughness has been characterized by atomic force microscopy (AFM). Also, depending on the concentration of the electrolyte, the mc-Si samples exhibit photoluminescence in the VIS range under UV excitation. The PL reveals the presence of nanocrystals on the surface of the etched samples. The surface structure is also optimized for an adequate placement of the metallic contact on top. Finally the solar cells were performed in order to investigate the dependence of the roughness, reflectance and photoluminescence to the solar efficiency.