Biaxially-textured photovoltaic film crystal silicon on ion beam assisted deposition CaF2 seed layers on glass

Abstract

We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF₂ seed layers using ion-beam assisted deposition, then coat the CaF₂ with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF₂ and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.