How grain boundaries in Cu(In,Ga)Se2 thin films are charged: Revisit

Potential measurements on Cu(In,Ga)Se2 thin films using scanning Kelvin probe force microscopy have been reported extensively to address grain-boundary (GB) recombination by examining GB charging. However, the results are highly inconsistent. We revisit this issue by measuring high- and low-quality wide-bandgap films and using a complementary method of scanning capacitance microscopy. Our results show consistent positively charged GBs in our high-quality films with minimal surface defects, except for the Σ3[112] GBs, which are charge neutral. We discuss possible artifacts due to surface defects when examining the GB charging and the role of GBs in the device performance.