Compositionally induced valence-band offset at the grain boundary of polycrystalline chalcopyrites creates a hole barrier

Abstract

First-principles calculations of modelgrain boundaries (GBs) in CuInSe 2 and CaGaSe 2 show that cation-terminated GBs have a valence-band offset with respect to the grain interior (GI). This offset repels holes from the GBs, thus depriving electrons there from recombination at the GB defects. Anion-terminated GBs have no such valence offset. CuGaSe 2 has, in addition, a conduction-band offset at the GB/GI interface, attracting electrons to the GBs. These features explain how polycrystalline chalcopyrite solar cells could outperform their crystalline counterparts.