Buffer layer of PEDOT:PSS/graphene composite for polymer solar cells.

High-efficiency polymer solar cells were made with a hydrophilic graphene oxide (GO) doped in poly(ethylene dioxythiophene) (PEDOT)-polystyrene sulfonic acid (PSS) composites using a structure of indium tin oxide/PEDOT:PSS:GO (40 nm)/poly(3-hexylthiophene-1,3-diyl) (P3HT)-[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:0.6, 100 nm)/LiF (1 nm)/Al (70 nm). The energy conversion efficiency eta was enhanced from 2.1 to 3.8% by doping GO into the PEDOT:PSS buffer layer under AM1.5G 100 mW cm(-2) illumination in air. The pre-annealing of GO makes energy conversion efficiency 1.8 times that of the device based on a pristine PEDOT:PSS buffer layer. Because of the low price and ease of preparation, soluble graphene will be a promising buffer layer used in photovoltaic applications. Furthermore, it can be used in other electronic applications.