Optical Confinement for Thin-Film Solar Cells by Gaseous HCL Etching

Abstract

Chemical vapour etching (CVE) with gaseous hydrochloride (HCl) at elevated temperatures offers the possibility to achieve either plane or structured surfaces depending on the temperature and the fraction of HCl in the carrier gas hydrogen. Therefore some process steps during the fabrication of a crystalline silicon thin film solar cell might be displaced or added by HCl etching. The removal of saw damage is possible and leads to a fraction of diffuse reflectance down to 18 % for the best actual process. In case of a solar cell based on the epitaxial wafer- equivalent pores can be generated by etching of deep pits and subsequent epitaxial deposition of the active silicon layer. Those pores can act as a reflector and lead to an increase of the optical path length of incoming light through the active layer, however the number of generated pores still has to be increased. Additionally facets with shallow gradients can be formed. A front side texturing consisting of a combination of different etching steps might be possible in future.