Vapor-Deposited Tungsten Carbide Nano-Dendrites As Sulfur-Tolerant Electrocatalysts For Quantum Dot-Sensitized Solar Cells

Recent advances in optoelectronic properties of quantum dots (QDs) have led to significant improvement in QD-sensitized solar cells (QDSCs); however, for practical utilization of these devices, performance of the constituent electrocatalytic counter electrodes (CEs) needs to be further enhanced. Pt CEs are prone to severe sulfur poisoning by polysulfide redox electrolytes in QDSCs, and Cu2S CEs with state-of-the-art activity are vulnerable to light-induced degradations. In this study, for the first time, tungsten carbide (W2C) films were used as CEs for QDSCs. Instead of the conventional methods of carbide nanomaterial synthesis that involve thermal treatments in toxic/explosive atmospheres, room-temperature vapor deposition was employed for the preparation of W2C electrodes, and dendritic nanostructures with large surface areas were obtained. Although the electronic structures of Pt and W2C are highly similar, W2C was completely inert to sulfur poisoning. This led to a substantial improvement in the electrocatalytic performance for polysulfide reduction, and similar to 27% enhancement in power conversion efficiency was achieved when Pt CEs were replaced with W2C CEs in QDSCs. Moreover, QDSCs comprising W2C CEs manifested excellent photostability, and they showed performances superior to those of QDSCs comprising state-of-the-art Cu2S electrodes within 40 min of operation, without any sign of drop in efficiency. (C) 2018 The Electrochemical Society.