Enhanced exciton separation through negative energy band bending at grain boundaries of Cu2ZnSnSe4 thin-films

Abstract

Local surface potential of Cu2ZnSnSe4 thin-films was investigated by Kelvin probe force microscopy. The surface potential profile across grain boundaries (GBs) shows a rise of 200-600 meV at GBs in a Cu-poor and Zn-poor film with 3.8 efficiency, which means positively charged GBs. In contrast, the GBs in a Cu-poor and Zn-rich film with 2 efficiency exhibit lowering of surface potential by 40 meV. The results indicate that GBs of Cu2ZnSnSe4 films play a role for exciton separation and governing defects for high efficiency could be not only CuZn but also VCu as explained theoretical predictions. © 2011 American Institute of Physics.