Characterization of wide bandgap a-SiO:H films and their application to thin film solar cells

Hydrogenated amorphous silicon oxide (a-SiO:H) films were prepared by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) using mixture of SiH4, H2 and CO2 source gas. The optical bandgap (Eopt) in the range between 1.90 and 2.02 eV was obtained by the variation of CO2 flow rate and H2 dilution. With increasing of H2 dilution, it was found that Eopt of the films increased and defect density reduced down to 1.69×10¹⁶ cm⁻³. The high open-circuit voltage (Voc) of 1.04 V was achieved for a single-junction amorphous silicon solar cells using optimized a-SiO:H as intrinsic layer (i-layer thickness = 120 nm, Jsc = 7.92 mA/cm², FF = 0.64, η = 5.24%). Experimental results indicated that wide bandgap a-SiO:H films are promising material for use as intrinsic layer in top cell structure of multi-junction solar cells.