Graphene Quantum Dots Band Structure Tuned by Size for Efficient Organic Solar Cells

The electronic states of graphene quantum dots (GQDs) can be tuned by varying the lateral size and edge structure, which further influence their optoelectronic properties and the applications. Herein, three kinds of GQDs with different lateral size are prepared by photon-Fenton reaction and separated through gel column chromatography, and their effects on the photovoltaic performances of inverted organic solar cells based on the poly(3-hexylthiophene) (P3HT) and poly(3-hexylthiophene)/(6,6)-phenyl-C61 butyric acid methylester (PCBM) blend films are studied systematically. In comparison with P3HT:PCBM cells, the power conversion efficiency of the P3HT:PCBM solar cells containing 0.8% of GQDs-blue, GQDs-green, and GQDs-orange can be increased from 3.06% to 3.54%, 4.43%, and 3.73% with a short-circuit current density of 10.3, 13.34, and 11.19 mA cm(-2). It is illustrated also that the band structures (electronic energy states) tuned mainly by their lateral size of GQDs are the crucial factor to dominate their photovoltaic preferences as additives in conventional P3HT:PCBM solar cells.