Damage-free reactive ion etch for high-efficiency large-area multi-crystalline silicon solar cells

Abstract

Texturing of silicon (Si) wafer surface is a key to enhance light absorption and improve the solar cell performance. While alkaline texturing of single-crystalline Si (sc-Si) wafers was well established, no chemical solution has been successfully developed for multi-crystalline Si (mc-Si) wafers. Reactive-ion-etch (RIE) is a promising technique for effective texturing of both sc-Si and mc-Si wafers, regardless of crystallographic characteristics, and more suitable for thin wafers. However, due to the use of plasma source generated by high power, the wafer surface gets a physical damage during the processing, which requires an additional subsequent damage-removal wet processing. In this work, we developed a damage-free RIE texturing for mc-Si solar cells. An improved self-masking RIE texturing process, developed in this study, produced ∼0.7% absolute efficiency gain on 156×156 mm 2 mc-Si cells, where the gas ratio and the plasma power density were keys to mitigate the plasma-induced-damage during the RIE processing while maintaining decent surface reflectance. In the self-masking RIE texturing, a mixture of SF 6/Cl 2/O 2 gases was found to significantly affect the surface morphology uniformity and reflectance, where an optimal etch depth was found to be 200–400 nm. We achieved J sc gain of ∼1.3 mA/cm 2 while maintaining decent FFs of ∼0.78 without a V oc loss after optimization of firing conditions.