Simulating the Role of TCO Materials, their Surface Texturing and Band Gap of Amorphous Silicon Layers on the Efficiency of Amorphous Silicon Thin Film Solar Cells

In this work, through modeling we propose how the choice of the TCO material, its texturing and optimization of band gap of a-Si:H layers help to increase the efficiency of a-Si:H solar cells. While selecting plane and textured indium tin oxide (ITO) and zinc oxide (ZnO) as TCOs, the solar cell parameters and performance are examined as a function of band gap of different a-Si:H layers. The optimum band gap values of 2.1 eV, 1.9 eV and 1.85 eV are obtained for p, i and n-layers of a-Si:H with maximum efficiencies of similar to 15.5 % and 17.7 % using plane ITO and ZnO contacts respectively. Interestingly, the conversion efficiency is further increased to similar to 16.3 % and 18.6 % when textured ITO and textured ZnO are used as TCOs. Moreover the higher efficiencies with ZnO-based contact than ITO-based contact can be explained due to slightly higher drift velocity of holes nearer to the junction and little improved optical properties which may also attributes to the enhanced trapping of the light. These results are very encouraging and may help in developing a-Si:H based solar cell technology for thin films