Defect segregation at grain boundary and its impact on photovoltaic performance of CuInSe2

Defect segregations at grain boundaries (GBs) of polycrystalline thin-film absorber are crucial to solar cell performance. The Sigma 3(114) GBs in CuInSe2 (CIS) have been studied through first-principle calculations. We reveal that the intrinsic CIS GBs produce deep gap states, which act as nonradiative recombination centers. However, the segregation of Cu-In and O-Se at GBs can clean the gap states and lead to electrically benign behavior. Our results suggest that the defect segregation at GBs could be an important feature for high efficiency CIS-based photovoltaic solar cells and it provides a general guidance for engineering GBs in other chalcogenide polycrystalline devices. (C) 2013 AIP Publishing LLC.