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 similar to 1-mu m-thick intrinsic layer, we obtained a short-circuit current density J(sc) = 24.6 mA/cm(2) and conversion efficiency E-ff = 9.47%. By increasing the nc-Si:H layer to similar to 3.1 mu m, we attained a J(sc) > 30 mA/cm(2). 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/cm(2) and high-cell efficiency of 8.8% were attained using a 2.5-mu m-thick nc-Si:H cell with an nc-SiOx:H n-layer.