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 Cu(3)MCh(3) (M = Sb, Bi; Ch = S, Se) family of materials. Cu3BiS3 contains bismuth, a nontoxic heavy metal that has a 6s(2) electronic structure akin to halide perovskites that have demonstrated excellent properties, and the sulfosalt crystallizes in the P2(1)2(1)2(1) 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 (similar to 10(5) cm(-1)), carrier mobilities in the range of 0.4-90 cm(2) (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.