Single-Component Damage-Etch Process for Improved Texturization of Monocrystalline Silicon Wafer Solar Cells

A new saw damage-etch process based on a hot sodium hypochlorite (NaOCl) solution is reported here. This process performs simultaneous damage removal and oxide masking of raw c-Si wafers in a single step. NaOCl is a strong oxidizing agent, and during the NaOCl damage-etch process, the oxide grown remains present even after the completion of the process. This oxide layer acts as protective mask during alkaline texture to form uniform and small (similar to 2-4 mu m height) pyramids on the < 1 0 0 > Si wafer surface. Unlike chemical vapor deposited silicon nitride or silicon dioxide protective masking processes reported by other researchers, this new damage-etch process is cost effective. It is also a single-component damage-etch process using only NaOCl solution. Thus, it involves easy bath preparation and performs in situ chlorine cleaning. Using the new damage-etch process, optimized texturing of the wafers is ascertained by electron microscopy and reflectivity studies of the textured surfaces. This new process is applied in the industrial R&D pilot line of the Solar Energy Research Institute of Singapore (SERIS) to fabricate screen-printed 156-mm pseudosquare p-type solar cells with tube-diffused emitters to yield efficiencies of over 18%.