Polycrystalline silicon solar cells on mullite substrates

Polycrystalline silicon layers have been grown on various alumino-silicate substrates in a rapid thermal chemical vapor deposition (RTCVD) system at high temperatures (>1000°C). Structural analysis shows a columnar growth with grain sizes up to 15 μm and growth rates up to 5 μm/min. Solar cell devices on this fine-grained Si material result in a short-circuit current of about 13 mA/cm² but a poor open-circuit voltage (<0.4 V). Larger grains obtained by the zone melting recrystallization (ZMR) technique boosted the current up to 26.1 mA/cm², thanks to the light-trapping by the mullite substrate. Best efficiency is 8.2% on a 1 cm² cell made on a 20 μm thick poly-Si layer.