Radio frequency plasma deposited boron doped high conductivity p-type nano crystalline silicon oxide thin film for solar cell window layer

Wide band gap p-type nano crystalline silicon oxide (p-nc-SiO:H) window layer is useful for multi junction solar cells. We prepared such a material by using high hydrogen dilution and low plasma power that shows high optical gap as well as high conductivity. By varying CO₂ flow rates of from 0.3 to 2.5 sccm we obtained the films with crystallite volume fraction (X_c) ranging from 43.7% to 4.5%, while by decreasing the plasma power density from 426, to 28 mW/cm² the X_c was observed to increase from 14.0% to 45.8%. At a high plasma power the hydrogen dilution did not show significant change in film properties. The electrical conductivity and activation energy was observed to be favorable at low plasma power density, which was 3.4 × 10^-2 S cm^-1 and 0.102 eV respectively at 28 mW/cm² plasma power density. It is expected that at a low plasma power a large number of SiH₃ radicals actively take part in film deposition, leading to an improved film properties. Solar cells fabricated with the selected p-nc-SiO:H, shows improved short wavelength response of the quantum efficiency, indicating the advantage of using such p-type materials. The optical gap of these p-nc-SiO:H films were in the range of 1.784 to 2.130 eV.