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.
Bibliographical noteFunding Information:
This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea (No. 10037233), by KRCF (Korea Research Council of Fundamental Science & Technology), and KIER (Korea Institute of Energy Research) for “NAP (National Agenda Project) program.” This work was supported in part by MEST and DGIST (10-BD-0101, Convergence Technology with New Renewable Energy and Intelligent Robot).