Soluble P3HT-Grafted Graphene for Efficient Bilayer-Heterojunction Photovoltaic Devices

CH2OH-terminated regioregular poly(3-hexylthiophene) (P3HT) was chemically grafted onto carboxylic groups of graphene oxide (GO) via esterification reaction. The resultant P3HT-grafted GO sheets (G-P3HT) are soluble in common organic solvents, facilitating the structure/property characterization and the device fabrication by solution processing. The covalent linkage and the strong electronic interaction between the P3HT and graphene moieties in G-P3HT were confirmed by spectroscopic analyses and electrochemical measurements. A bilayer photovoltaic device based on the solution-cast G-P3HT/C-60 heterostructures showed a 200% increase of the power conversion efficiency (eta = 0.61%) with respect to the P3HT/C-60 counterpart under AM 1.5 illumination (100 mW/cm(2)).