Few-layered graphene quantum dots as efficient hole-extraction layer for high-performance polymer solar cells

In this study, we demonstrate that few-layered graphene quantum dots (F-GQDs) can be used as hole-extraction layer (HEL) for high efficiency polymer solar cells (PSCs). As a new class of HEL material, graphene oxide (GO) is not suitable for polymer solar cells (PSCs) based on highly efficient donor polymers due to the relatively low work function and the poor film-forming property of GO. To circumvent these two problems, we develop F-GQDs with a small size of about 4 nm and high content of periphery COOH groups. The small size of F-GQD ensures an excellent film-forming capability and the abundant COOH groups increase the work function of F-GQD to 5.26 eV from 5.01 eV of GO. As the result, when used as HEL in high efficiency PSC devices with PTB7:PC71BM or PCDTBT:PC71BM as the active layer, F-GQDs outperforms GO and the state-of-the-art HEL, PEDOT:PSS. These results demonstrate the great potential of F-GQD as efficient HELs to achieve high-performance PSCs. (C) 2015 Published by Elsevier Ltd.