Microstructure and photovoltaic properties of low temperature polycrystalline silicon solar cells fabricated by VHF-GD CVD using fluorinated gas

Polycrystalline silicon (poly-Si) photovoltaic devices were fabricated from SiF4, H2 and SiH4 gas mixtures using very high frequency (100 MHz) chemical vapor deposition (VHF CVD). The gas flow rate and the SiF4/H2/SiH4 ratio were optimized for low temperature, device quality poly-Si growth. The n-layers used for the n/i/Pt Schottky diodes and n/i/p solar cells were deposited at 300°C and i-layers at 100–300°C to provide a seed layer for subsequent i-layer growth. The open circuit voltage increased with i-layer growth temperature in the n/i/Pt Schottky diodes. However, the optimal fill factor (FF) occurred at a ∼200°C i-layer growth temperature. The FF decreased at temperatures >250°C. The best solar cells had short circuit current of 24 mA/cm2 and energy conversion efficiency of 6.22%. Also, it was possible to prepare high efficiency solar cells at relatively high growth rates, 0.5 nm/s, by optimizing the SiH4 flow rate.