Eco-Friendly AgBiS2 Nanocrystal/ZnO Nanowire Heterojunction Solar Cells with Enhanced Carrier Collection Efficiency

AgBiS2 nanocrystals (NCs) are nontoxic, lead-free, and near-infrared absorbing materials. Eco-friendly solar cells were constructed using interdigitated layers of ZnO nanowires (NWs) and AgBiS2 NCs, with the aim of elongating the otherwise short carrier diffusion length of the AgBiS2 NC assembly. AgBiS2 NCs were uniformly infiltrated into the ZnO NW layers using a low-cost and easily scalable dip coating method. The resulting ZnO NW/AgBiS2 NC interdigitated structures provided efficient carrier pathways in constructed nanowire solar cells (NWSCs), composed of a transparent electrode/ZnO NW/AgBiS2 NC interdigitated layer/P3HT hole transport layer/Au. The photocurrent external quantum efficiency (EQE) in the visible to near-infrared regions was enhanced compared to those of the control solar cells made with ZnO/AgBiS2 tandem layered structures. The maximum EQE for the NWSCs reached 82% in the visible region, which is higher than the EQE values previously reported for solar cells fabricated with ZnO/AgBiS2 NCs. Air stability tests on unsealed NWSCs demonstrated that 90% or more of the initial power conversion efficiency was maintained even after 6 months.