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

Few-layered graphene quantum dots (F-GQD) with a small size of about 4 nm and high content of periphery COOH groups show excellent film-forming capability and high work function of 5.26 eV. When used as hole-extraction layer (HEL) in polymer solar cells (PSCs) based on high efficiency donor polymers, F-GQD outperforms graphene oxide and PEDOT:PSS.