Low temperature (<100 °C) fabrication of thin film silicon solar cells by HWCVD

Abstract

Amorphous silicon films have been made by HWCVD at a very low substrate temperature of ≤ 100 °C (in a dynamic substrate heating mode) without artificial substrate cooling, through a substantial increase of the filament–substrate distance ( 80 mm) and using one straight tantalum filament. The material is made at a reasonable deposition rate of 0.11 nm/s. Optimized films made this way have device quality, as confirmed by the photosensitivity of > 105. Furthermore, they possess a low structural disorder, manifested by the small Γ/2 value (half width at half maximum) of the transverse optic (TO) Si–Si vibration peak (at 480 cm− 1) in the Raman spectrum of 30.4 cm− 1, which translates into a bond angle variation of only 6.4°. The evidence gathered from the studies on the structure of the HWCVD grown film by three different techniques, Raman spectroscopy, spectroscopic ellipsometry and transmission electron microscopy, indicate that we have been able to make a photosensitive material with a structural disorder that is smaller than that expected at such a low deposition temperature. Tested in a p–i–n solar cell on Asahi SnO2:F 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 solar cell made at such a low temperature.