Correlative transmission Kikuchi diffraction and atom probe tomography study of Cu(In,Ga)Se2 grain boundaries

Torsten Schwarz, Guillaume Stechmann, Baptiste Gault, Oana Cojocaru-Mirédin, Roland Wuerz, Dierk Raabe

Index: 10.1002/pip.2966

Full Text: HTML

Abstract

We combined transmission Kikuchi diffraction and atom probe tomography techniques to investigate the relationship between the structure and chemistry of grain boundaries in Cu(In,Ga)Se2 thin films. Kikuchi patterns with the tetragonal structure of Cu(In,Ga)Se2 were simulated to emphasize the pseudosymmetry issue in this material system and, hence, the orientation determination ambiguity in case of indexing with a cubic zinc-blende structure. We compared these patterns with experimental data. We detect an elemental redistribution at random high-angle grain boundaries but no chemical fluctuations at Σ3 twin boundaries. The atom probe tomography analyses reveal Cu depletion as well as In and Se enrichment at random grain boundaries and, at some random grain boundaries, a slight Ga depletion. This In on Cu scenario is accompanied by cosegregation of Na and K originating from the soda-lime glass substrate. The amount of impurity segregation does vary not only from one grain boundary to another but also along an individual grain boundary. Hence, our results suggest that the degree of passivation of detrimental, nonradiative recombination centers does differ not only between Σ3 twin boundaries and random grain boundaries but also within the same random grain boundary. We combined transmission Kikuchi diffraction and atom probe tomography to investigate the relationship between the structure and chemistry of grain boundaries in Cu(In,Ga)Se2 thin films. We detect an elemental redistribution at random high-angle grain boundaries but no chemical fluctuations at Σ3 twin boundaries. We observe Cu and a slight Ga depletion as well as In and Se enrichment at random grain boundaries. This In on Cu scenario is accompanied by cosegregation of Na and K impurities.