Photo‐enhanced catalytic activity of spray‐coated Cu 2 SnSe 3 nanoparticle counter electrode for dye‐sensitised solar cells

Cu 2 SnSe 3 nanoparticles are synthesised using oleylamine as both a solvent and capping agent and spray coated to form dye‐sensitised solar cell (DSSC) counter electrodes (CEs) using earth‐abundant elements. The film requires annealing at only 400 °C in nitrogen, which is a lower temperature than previous reports of both Cu 2 SnSe 3 and Cu 2 ZnSnSe 4 films, also avoiding the use of Se gas. The composition and phase of the material is confirmed to be kesterite Cu 2 SnSe 3 . DSSCs using Cu 2 SnSe 3 CEs give a power conversion efficiency of 4.87%, compared to 5.35% when using Pt. Electrochemical impedance spectroscopy indicates that the performance of the Cu 2 SnSe 3 CE is enhanced under illumination, leading to a drop in the charge transfer resistance. This illumination‐induced enhancement of the catalytic activity provides a novel mechanism for the enhancement of CE performance in DSSCs.Photo‐excitation of the nanostructured Cu 2 SnSe 3 counter electrode provides a higher overpotential for electrolyte reduction, giving improved catalytic performance.