Graphene quantum dots-incorporated cathode buffer for improvement of inverted polymer solar cells

Graphene quantum dots (GQDs) are an emerging class of nanomaterials with unique photonic and electric properties. In this study, GQDs were prepared by a facile, inexpensive and high-yield hydrothermal method and were further used as a cathode buffer additive for inverted polymer solar cells due to a wide band gap (~3.3 eV) and well-matched energy level between GQDs-cesium carbonate (GQDs-Cs2CO3) modified indium tin oxide (3.8 eV) and high occupied molecular orbit of [6,6]-phenyl-C61-butyric acid methyl ester (3.7 eV). In comparison to inverted polymer solar cells using cesium carbonate (Cs2CO3) buffer layer, the power conversion efficiency of GQDs-Cs2CO3 based device showed 22% enhancement from 2.59% to 3.17% as a result of enhanced exciton dissociation and suppressed free charge recombination at cathode/polymer active layer interface by GQDs. This work provides a new application of GQDs in organic electronic devices.