Control of the interfacial charge transfer resistance to improve the performance of quantum dot sensitized solar cells with highly electrocatalytic Cu-doped SnS counter electrodes

Abstract High charge transfer resistance at the interface between counter electrodes (CEs) and sulfide/polysulfide based electrolytes is responsible for the low photoelectrochemical performance of quantum dot sensitized solar cells (QDSSCs). Here, for the first time, we fabricated highly electrocatalytic and stable Cu-doped SnS CEs by inexpensive chemical bath deposition (CBD) method, to control the interfacial charge transfer resistance in QDSSCs and increase their photovoltaic performance. TiO2/CdS/CdSe/ZnS photoanodes and an aqueous polysulfide electrolyte were used to fabricate the QDSSCs with CEs. The QDSSCs with a 10%-Cu-doped SnS CE achieved an outstanding conversion efficiency of 4.07% under standard simulated AM 1.5 illumination, exceeding that of a cell with an undoped SnS CE (2.80%). The surface morphologies of SnS CEs with different Cu contents were significantly different. The voids between SnS nanoparticles deposited on fluorine-doped tin oxide (FTO) substrate were reduced upon the uniform distribution of Cu dopants. The Cu-doped SnS CE had significantly improved electrocatalytic activity for catalysis during the reduction of electrolyte, low charge transfer resistance at the CE/electrolyte interface, and fast electron transport from SnS surface to the electrolyte to regenerate the redox couple. These findings may inspire the design of efficient CEs for the large-scale production of next-generation QDSSCs.