Controlling Solution Surface Tension for the Cleaning of Small Size Textured Si Surface to Obtain Extremely Low Surface Recombination Velocity of 0.6 cm/s

摘要

Reducing thickness of crystalline silicon (c-Si) wafers to <100 μm is one of the keys to low-cost solar cells. On such thin c-Si wafers, a reduction in the size of textures is neces-sary to minimize c-Si losses by texturing process and to keep the robust property in cell fabrication processes. To obtain small textures with a size <2 μm through alkaline anisotropic etching, we have already established “Microparticle-As-sisted Texturing” (MPAT) process . However, cleaning of such small texture surface is always challenging. We have revealed the importance of surface cleaning to obtain high quality passivation . Therefore, in this work, we aimed to develop a suitable cleaning procedure for the small texture surface. We discovered a novel effect of mixing methanol (CH_3OH) with hydrochloric acid (HF) on surface passivation quality of the c-Si surface. Surface recombination velocity (SRV) decreases from 3.5 down to 0.6 cm/s when methanol is mixed with HF. It is found that methanol reduces the sur-face tension of HF solution on the c-Si surface, leading to uniform chemical reaction or effective chemical cleaning. We named this finding “Methanol-Assisted Cleaning (MAC)” process.