Solution-Processable Cu₃BiS₃ Thin Films: Growth Process Insights and Increased Charge Generation Properties by Interface Modification

Cu₃BiS₃ thin films are fabricated via spin coating of precursor solutions containing copper and bismuth xanthates onto planar glass substrates or mesoporous metal oxide scaffolds followed by annealing at 300 °C to convert the metal xanthates into copper bismuth sulfide. Detailed insights into the film formation are gained from time-resolved simultaneous small and wide angle X-ray scattering measurements. The Cu₃BiS₃ films show a high absorption coefficient and a band gap of 1.55 eV, which makes them attractive for application in photovoltaic devices. Transient absorption spectroscopic measurements reveal that charge generation yields in mesoporous TiO₂/Cu₃BiS₃ heterojunctions can be significantly improved by the introduction of an In₂S₃ interlayer, and long-lived charge carriers (t_50% of 10 μs) are found.