Design and Optimization of Photonic Crystal Diffraction Grating Based Efficient Light Trapping Structure for GaAs Thin Film Solar Cell

The paper presents a design optimization for an efficient light-trapping structure to significantly increase the efficiency of thin-film GaAs solar cells. The light trapping structure (LTS) includes single planar Anti-Reflection coating (ARC) layer at the top assisted by 2D Photonic Crystals (PhC) diffraction grating and Distributed Bragg Reflector (DBR) at the back. Dielectric 2D PhC between the active layer and DBR diffracts light at oblique angles within the absorber and provides lossless diffraction of photons, and hence increasing the photon path length within the active layer. As a representative example, the LTS geometry for 500 nm GaAs active layer is optimized to obtain maximum absorption. We have also shown two material combinations possible for the back trapping structure keeping electrical conductivity in mind. The paper also reports the enhancement in optical absorption for the proposed structure as compared to the solar cell structure consist only ARC and DBR.