Photo-enhanced catalytic activity of spray-coated Cu₂SnSe₃ nanoparticle counter electrode for dye-sensitised solar cells

Cu₂SnSe₃ 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 Cu₂SnSe₃and Cu₂ZnSnSe₄ films, also avoiding the use of Se gas. The composition and phase of the material is confirmed to be kesterite Cu₂SnSe₃. DSSCs using Cu₂SnSe₃ 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 Cu₂SnSe₃ 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. (Figure presented.). Photo-excitation of the nanostructured Cu₂SnSe₃ counter electrode provides a higher overpotential for electrolyte reduction, giving improved catalytic performance.