Down-Conversion Effect Created by SiO x Films Obtained by HFCVD and Applied over Pn-Junctions

A top coating film of silicon oxide off-stoichiometry (SiO x ) was used on silicon solar cells to improve its electrical properties by the Down-conversion effect. The SiO x films were obtained by hot filament chemical vapor deposition (HFCVD) with different hydrogen flow (H F ) and different distances: the wire-source distance and the source-substrate distance, and by consequence, with different temperatures. Transmittance spectra showed 0% of transmittance in the UV region. The amount of atomic silicon % in the SiO x films was changed with the variation of the mentioned parameters, as demonstrated with the Energy-Dispersive X-ray Spectroscopy (EDS) and the Fourier transform infrared spectroscopy (FTIR) results. The SiO x films showed a wide Photoluminescence (PL) between 400 nm and 900 nm when they were excited with UV light. The SiO x films were applied as a top coating on pn junctions of silicon substrate to develop silicon solar cells. The J-V measurements and the external quantum efficiency (EQE) of the solar cells were obtained, as well as the open circuit voltage (V oc ), short-circuit current density (J sc ), the efficiency (η) and the fill factor (FF). The silicon solar cells with the SiO x top coatings, with the highest PL, showed the highest efficiency. The best figures of merit were η = 5.9%, V oc = 480 mV, J sc = 27 mA/cm 2 , P max = 5.5 mW and FF = 0.4.