Optical properties of transparent conducting oxide sculptured thin films for application in thin film silicon photovoltaics

Oxide thin films serving dual roles of transparent conductor and optical filter have been proposed on the basis of the sculptured thin film (STF) concept. This concept entails variations in the polar and azimuthal angles (Θ, Φ) of the deposited flux with respect to the substrate normal, that are performed step-wise or continuously during film growth in order to achieve step-wise or continuous variations in the principal dielectric tensor components. If these variations are sufficient in magnitude, then multilayered or graded films can be designed as optical filters and integrated into thin film photovoltaic (PV) structures to minimize reflection and absorption losses. In this initial report, we demonstrate the potential effectiveness of multilayered, index-modulated ZnO as an improved back-reflecting dielectric for thin film silicon PV structures. We also describe the structure and optical properties of SnO₂ prepared by electron-beam evaporation, demonstrating that the ordinary index of refraction variation required for multilayer filters is achievable in practice.