Impact of silicon wafer thickness on photovoltaic performance of crystalline silicon heterojunction solar cells

The impact of Si wafer thickness on the photovoltaic performance of hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells was examined from the optical and electrical points of view. Optical characterization of c-Si wafers of various thicknesses showed that a realistic light-trapping scheme, i.e., pyramidally textured Si wafers with a dielectric antireflection coating and a back reflector, realizes an efficient quasi-Lambertian light absorption enhancement, even for very thin wafers. This indicates that high photocurrent densities are achievable by using the realistic light-trapping scheme, assuming that the parasitic absorption loss is minimized. The potentials of open-circuit voltage (VOC) and the fill factor (FF) of thin c-Si cells were investigated using thin c-Si wafers passivated with intrinsic/doped amorphous silicon film stacks. It was experimentally confirmed that the implied VOC increases steadily with decreasing wafer thickness down to 30 µm, while the implied FF weakly depends on the thickness. As a result of the trade-off between light absorption and implied VOC, a high implied efficiency is expected for a wide range of wafer thicknesses. The VOC increase by thinning the wafer was also experimentally confirmed in an a-Si:H/c-Si heterojunction cell with a thickness below 60 µm, resulting in a conversion efficiency of 21.0%.