Advances in Light Trapping for Hydrogenated Nanocrystalline Silicon Solar Cells

We optimized Ag/ZnO back reflectors (BR) for hydrogenated nanocrystalline silicon (nc-Si:H) solar cells by independently changing the textures of the Ag and ZnO layers. We found that Ag/ZnO with textured Ag and thin ZnO provides the highest nc-Si:H solar cell efficiency. Optimized Ag texture with an rms = 40 nm effectively scatters light without seriously degrading the nc-Si:H material quality. Using this type of BR and nc-Si:H cells with ~1-μm-thick intrinsic layer, we obtained a short-circuit current density J_sc = 24.6 mA/cm² and conversion efficiency Eff = 9.47%. By increasing the nc-Si:H layer to ~3.1 μm, we attained a J_sc >;30 mA/cm². In order to increase the J_sc further, we increased the texture of the ZnO layer. With highly textured Ag/ZnO BRs, the J_sc was increased. However, the high textures caused poor fill factors, and hence, relatively low efficiency. By using nanocrystalline silicon-oxide (nc-SiOx:H) to replace both the n-layer and dielectric layer, the texture-induced deterioration of nc-Si:H material quality was suppressed and the cell structure was simplified by removing the ZnO, conventional n-layer, n/i buffer layer, and the seed layer. A high J_sc over 27 mA/cm² and high-cell efficiency of 8.8% were attained using a 2.5-μm-thick nc-Si:H cell with an nc-SiOx:H n-layer.