Scavenging of excess Cu atoms in CuInS2 films by sulphur annealing

We have investigated Cu-In-S films with positive non-molecularity Delta m = ([Cu]/[ln]) - 1 grown by different preparation techniques such as coevaporation, sulphurization of stacked elemental layers, and spray pyrolysis. Using X-ray diffraction and electron spectroscopy, we have looked for the formation of Cu chalcogenide secondary phases. It was found that films grown by coevaporation and sulphurization establish a CuS overlayer at the front surface of the films. The CuS segregation is missing for films which are grown by spray pyrolysis, however it can be induced for these films by annealing in H2S. It is shown that the sulphur acts as scavenger for excess Cu atoms in the CuInS2 matrix. Furthermore, we prove that the induced CuS segregation promotes the recrystallization of the films.