Light Trapping in Thin Film Polycrystalline Silicon Solar Cell using Diffractive Gratings

We report on an investigation of a periodic diffractive Si grating structure used to enhance the absorption in thin film Si cells with an active layer 2 μm by modelling. The media of the grating can be air (n=1.0) with detached back reflector or coated with a layer of dielectric material, SiO2 (n=1.4) as a buffering layer. Gratings with periods of 500, 800 and 1200 nm were located on the rear side of the cell, with depths from 150 nm to 300 nm. The reason to use a shallow grating depth is to ensure smallest material loss. The influence of the grating period, depth and surrounding media on the short circuit was investigated and the optimal grating parameters were obtained. A structure which has a 500 nm period, 150 nm depth, in air media gives the best light trapping, with 76.5% enhancement of short current density (Jsc).