Synthesis of wittichenite Cu3BiS3 thin films by sulfurizing thermally evaporated Cu-Bi metallic stacks

Wittichenite Cu3BiS3 thin films have received significant interest as light harvesters owing to their suitable optoelectronic properties and presence of earth-abundant, and non-toxic elements. We have synthesized Cu3BiS3 thin films by a two-stage process; in which, Cu/Bi/Cu metallic stacks were thermally evaporated and then sulfurized at 400 degrees C for 10-60 min in a quartz tubular furnace. The influence of sulfurization time on the structural, microstructural, compositional, optical, and electrical properties of the films was investigated. The results revealed that the films were orthorhombic Cu3BiS3 with the following lattice parameters: a = 0.768 nm; b = 1.043 nm; and c = 0.674 nm. Films uniformity, compactness, and crystal grain size increased upon increasing the sulfurization duration. On increasing the sulfurization time, the elemental stoichiometry of the films improved, and the direct optical bandgap increased from 1.38 to 1.40 eV. Additionally, Cu3BiS3 films exhibited p-type electrical conductivity and the electrical resistivity decreased with the increasing sulfurization time. Consequently, the Cu3BiS3 films synthesized at 30-and 60-min sulfurization durations can be applied to thin-film solar cells.