Graphene quantum dots as the hole transport layer material for high-performance organic solar cells

We present an investigation of organic photovoltaic (OPV) cells with solution-processable graphene quantum dots (GQDs) as hole transport layers (HTLs). GQDs, with uniform sizes and good conductivity, are demonstrated to be excellent HTLs in both polymer solar cells (PSCs) and small-molecule solar cells (SMSCs) with the blend of poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT:PC61BM) and small molecule DR3TBDT:[6,6]-phenyl-C-71-butyric acid methyl ester (DR3TBDT:PC71M) as the active layer, respectively. The PSCs and SMSCs based on GQDs yield power conversion efficiencies of 3.51% and 6.82%, respectively, both comparable to those of solar cells with PEDOT:PSS as the HTLs. In addition, the cells with GQDs as HTLs exhibit much more reproducible performance and longer lifetime. In light of the high stability, low cost and easy processing, these results indicate that GQDs can be potentially used to replace PEDOT: PSS for producing high-performance and stable organic photovoltaic cells.