Antireflective properties of Al2O3/SiO2 multilayer stacks for GaAs solar cells

Abstract

Multilayer (ML) thin films are an optical engineering strategy to address reflectivity losses in GaAs photovoltaic devices, enhancing the power conversion of light around a single wavelength. Inspired by the enhanced response of periodic ML Bragg mirrors, the authors introduce quite simple antireflective designs based on two periods and single periods of Al2O3/SiO2 bilayer stacks. The reflectivity losses of the systems are evaluated with the aid of numerical simulations, and their dimensions are optimized to enhance the transmission of plane waves towards GaAs substrates. Reflectivity losses are evaluated at angles off the normal for s- and p-polarized light, exhibiting gains at broader angles and the quenching of undesired s-to-p optical anisotropy, inherent to GaAs substrates. ML stacks were fabricated by RF sputtering deposition on GaAs-n and p+ type substrates and characterized by UV-Vis spectroscopy techniques to evaluate the role of carriers on coating performance.