Solution Processing Cu₃BiS₃ Absorber Layers with a Thiol–Amine Solvent Mixture

There is a need to develop more Earth-abundant, less toxic, and more environmentally stable solar absorbers as the market demand for solar cells increases. Wittichenite (Cu3BiS3) is a sulfosalt mineral that belongs to the Cu3MCh3 (M = Sb, Bi; Ch = S, Se) family of materials. Cu3BiS3 contains bismuth, a nontoxic heavy metal that has a 6s2 electronic structure akin to halide perovskites that have demonstrated excellent properties, and the sulfosalt crystallizes in the P212121 space group with a near-optimal band gap for single-junction thin film solar cells. We report the utility of thiol–amine solvent mixtures to dissolve inexpensive bulk CuO and Bi2S3 precursors to produce a free-flowing semiconductor ink. Good quality and phase-pure Cu3BiS3 thin films were solution processed from this ink upon mild annealing. The p-type thin films possess a direct band gap of 1.47 eV with a high absorption coefficient through the visible (∼105 cm–1), carrier mobilities in the range of 0.4–90 cm2 (V·s)−1, and a strong photoelectrochemical current response. The optoelectronic properties of Cu3BiS3 thin films deposited using this thiol–amine chemistry suggest that it is a favorable candidate as a solution-processable solar absorber.