Broad range refractive index engineering of SixNy and SiOxNy thin films and exploring their potential applications in crystalline silicon solar cells

Abstract

Silicon nitride (SixNy) and silicon oxynitride (SiOxNy) are materials that can find multifarious application in solar cells by tuning their microstructure and optical properties. In this work we have investigated a series of SixNy and SiOxNy films deposited by rf-PECVD at a low temperature of 200 °C having different compositional and optical properties by changing the gas mixture ratio during deposition resulting in varying refractive index materials. The effect of varying gas ratio on the composition of these materials has been investigated comprehensively by X-ray Photoelectron Spectroscopy (XPS) and the bond analysis using Fourier Transform Infrared Spectroscopy (FTIR) thereby creating a material library to select materials of desired properties and bond composition for specific applications in solar cells. The structural and optical properties were also analysed using Micro-Raman spectroscopy, X-ray Diffraction (XRD), UV-VIS-NIR spectrophotometer and ellipsometry. The films were found to be amorphous, hydrogenated, compact, presents high deposition rates and needs lesser thermal budget. In order to demonstrate their multifaceted application potential, we have fabricated multilayer anti-reflection coatings (ARC), novel Rugate ARC, dielectric Bragg mirrors using SiOxNy/SixNy multi layers as back reflectors for thin crystalline silicon (c-Si) wafers as well as the passivation of c-Si. The novel bilayer passivation stack over CZ p-type c-Si wafers using SiOxNy/SixNy presented a minority carrier lifetime of 169 μs with an implied Voc of 673 mV.