On the chemistry of grain boundaries in CuInS2 films

We conducted correlated transmission Kikuchi diffraction and atom probe tomography measurements to investigate the relationship between the structure and chemistry of grain boundaries in Cu-rich and Cu-poor sulfide chalcopyrite CuInS2 thin-films. We detect different elemental redistributions at random high-angle grain boundaries, Sigma 9 twin boundaries and stacking faults in the Cu-rich and Cu-poor film but no chemical fluctuations at Sigma 3 twin boundaries. For the Cu-rich CuInS2 thin-film, our atom probe tomography analyses reveal Cu enrichment as well as In and S depletion at random grain boundaries, Sigma 9 twin boundaries and stacking faults. Hence, we may observe a 'Cu on In' scenario, which is accompanied by co-segregation of Na and C. In contrast, for the Cu-poor CuInS2 thin-film, our analyses show Cu depletion and In enrichment at random grain boundaries and at the vast majority of stacking faults. For S we do not observe a clear trend. Therefore, for the Cu-poor CuInS2 thin-film we may observe a 'In on Cu' scenario, which is accompanied by co-segregation of Na, K and O at the random grain boundaries but not at stacking faults. The amount of impurity segregation varies from one grain boundary to another in both thin-films.