Stability enhancement of CuS against Cu vacancy formation by Ag alloying.

As a potential solar absorber material, CuS has proved its importance in the field of renewable energy. However, almost all the known minerals of CuS suffer from spontaneous Cu vacancy formation in the structure. The Cu vacancy formation causes the structure to possess very high p-type doping that leads the material to behave as a degenerate semiconductor. This vacancy formation tendency is a major obstacle for this material in this regard. A relatively new predicted phase of CuS which has an acanthite-like structure was found to be preferable than the well-known low chalcocite CuS. However, the Cu-vacancy formation tendency in this phase remained similar. We have found that alloying silver with this structure can help to reduce Cu vacancy formation tendency without altering its electronic property. The band gap of silver alloyed structure is higher than pristine acanthite CuS. In addition, Cu diffusion in the structure can be reduced with Ag doped in Cu sites. In this study, a systematic approach is presented within the density functional theory framework to study Cu vacancy formation tendency and diffusion in silver alloyed acanthite CuS, and proposed a possible route to stabilize CuS against Cu vacancy formations by alloying it with Ag.