Bipolar transport observed through extraction currents on organic photovoltaic blend materials

Both electron and hole mobilities have been simultaneously measured through charge extraction by linearly increasing voltage on polymer heterojunction solar cells with varying stoichiometry of polymer and acceptor. The polymer is a low band gap copolymer of fluorene, thiophene, and electron accepting groups named APFO-Green 5, and the acceptor is [6,6]-phenyl-C-61-butyric acid methylester. Results are correlated to field effect transistor measurements on the same material system. A monotonous increase in mobility for both carrier types is observed with increased acceptor loading. (c) 2006 American Institute of Physics.