In this article, we report on the 3D optical simulation for 1D, 2D Photonic Crystal (PC) structures such as distributed Bragg reflector (DBR) and flattened light-scattering substrate (FLiSS) and for micro-pyramid structure performed by using Finite Difference Time Domain (FDTD) method. These structures are used at the rear side of the solar cell to increase the absorption in the active medium. A reflectancetransmittance study has been performed for the above structures by varying the different parameters. The FLiSS structures are modelled for different oxide materials (ZnO:Al, ZnO, ITO) in combination with a-Si:H and the reflectance spectra are compared. In DBR, the reflectance was measured for both different layer thicknesses and different periods. For micro-pyramid structure, the reflectance studies were performed at different heights and compared with the planar substrate. To further examine the effect of above structures on solar cell performance, an absorption study has been done in p-i-n solar cell with FLiSS structure at the rear side and compared it with the p-i-n cell alone. A photocurrent study of the p-i-n cell on FLiSS structure gives a maximum current of 26 mA/cm2 for 200 nm thick FLiSS. © 2019 Elsevier Ltd. All rights reserved.