Nanostructured Ni-doped CuS thin film as an efficient counter electrode material for high-performance quantum dot-sensitized solar cells

High electrocatalytic activity and low charge transfer resistance are the key factors of coutner electrodes (CEs) for high-performance quantum dot-sensitized solar cells (QDSSCs). Hence, it is challenging and highly deisrable to fabricate the CEs with high catalytic activity and low charge transfer resistance for QDSSCs. To address these issues, here, we design and prepare a new catalytic electrode by doping of nickel (Ni) ion in CuS for use as CEs in QDSSCs. The Ni-doped CuS CEs are fabricated via a facile chemcial bath deposition method. Scanning electron microscope study reveals that the Ni-doped CuS exhibits the surface morphology of nanoparticles over nanoflake structrues, while the CuS delivers the nanoflake structures. The Ni-doped CuS provides abundant active sites for reduction of polysulfide redox couple, higher electrical conductivity and offers excellent pathways for electron transfer, which yields the high electrocatalytic activity and delivers the lower charge transfer resistance at the interface of CE/electrolyte. As a result, the TiO2/CdS/CdSe QDSSCs with Ni-CuS yield a power conversion efficiency (eta) of 4.36% with short circuit current density (J(SC)) of 13.78 mA cm(-2), open-circuit voltage (V-OC) of 0.567 V, and fill factor (FF) of 0.558, which are much superior to that of device with CuS CE (eta = 3.24%; J(SC) = 10.63 mA cm(-2); V-OC = 0.567; FF = 0.546) under one sun illumination (AM 1.5G, 100 mW cm(-2)). Present work determines that Ni-doped CuS could be a promising CE material for QDSSCs due to its high electrical conductivity, excellent electrocatalytic activity, and lower charge transfer resistance.