Screen-printed Cu₃BiS₃-polyacrylic Acid Composite Coatings

A technique for preparing electrically conductive coatings of Cu₃BiS₃ powder in polyacrylic acid matrix is presented. Bi₂S₃ powder obtained by chemical precipitation was introduced into a freshly prepared CuS chemical deposition bath. After the initial nucleation period, CuS started to deposit on the Bi₂S₃ surface. The as-obtained CuS–Bi₂S₃ powder was mixed with polyacrylic acid aqueous solution, and the resulting mixture was used as a paste to form a screen-printed composite coating. Up to 200 °C the film behaves like a simple CuS film; the sheet resistance is around 100 and the crystallized phase in the composite is CuS (Covellite). When the temperature is equal or higher than 250 °C, atomic diffusion at the CuS–Bi₂S₃ interface is promoted, leading to the formation of the ternary compound Cu₃BiS₃ (Wittichenite) in the composite film. The formation of the compound depends on the temperature, relative abundance of the Bi₂S₃ and CuS components in the CuS–Bi₂S₃ pigment, as well as on the annealing atmosphere.