Polymer photovoltaic cells based on solytion-processable graphene and P3HT

A soluble graphene, which has a one-atom thickness and a two-dimensional structure, is blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction (BHJ) polymer photovoltaic cells.. Adding graphene to the P3HT induces a great quenching of the photoluminescence of the P3HT, indicating a strong electron/energy transfer from the P3HT to the graphene. In the photovoltaic devices with an ITO/PEDOT:PSS/P3HT:graphene/LiF/Al structure, the device efficiency increases first and then decreases with the increase in the graphene content. The device containing only 10wt % of graphene shows the best performance with a power conversion efficiency of 1.1%, an open-circuit voltage of 0.72 V, a short-circuit current, density of 4.0mA cm², and a fill factor of 0.38 under simulated AM1.5G conditions at 100 mW cm ² after an annealing treatment at 160° C for 10 min. The annealing treatment at the appropriate temperature (160° C, for example) greatly improves the device performance; however, an annealing at overgenerous conditions such as at 210° C results in a decrease in the device efficiency (0.57%). The morphology investigation shows that better performance can be obtained with a moderate content of graphene, which keeps good dispersion and interconnection. The functionalized graphene, which is cheap, easily prepared, stable, and inert against the ambient conditions, is expected to be a competitive candidate for the acceptor material in organic photovoltaic applications.