Low Temperature (< 100 °C) Fabrication of Thin Film Silicon Solar Cell by HWCVD

The aim of this research is to develop a suitable growth process for fabricating stress-free thin film silicon based solar cells on plastics such as PEN and PET. Employing HWCVD technique, through a substantial increase of the filament-substrate distance, silicon films could be made at a very low substrate temperature of about 100 degC without artificial substrate cooling. Optimized films made this way, have a remarkably low structural disorder, manifested by the very small (~30.4 cm^-1) Gamma/2 value of the transverse optic (TO) Si-Si vibration peak in the Raman spectrum, which translates into a bond angle variation of only ~6.4 degrees. This high structural order may be attributed to the deposition process where (i) the highly reactive radicals (such as SiH₂) are suppressed from reaching the substrate due to the large filament to substrate distance and (ii) absence of clusters (due to absence of ions). A photosensitivity of >10⁵ confirms the device quality of material. This result implies that we have been able to make a photosensitive protocrystalline type of material with a very small structural disorder. Tested in a p-i-n solar cell on Asahi SnO₂ coated glass (without ZnO at the back reflector), this i-layer gave an efficiency of 3.4%. To our knowledge, this is the first report of a HWCVD thin film silicon cell made at such a low temperature