Photoresponse of organic field-effect transistors based on conjugated polymer/fullerene blends

Results on photoresponsive organic field-effect transistors (photOFETs) based on conjugated polymer/fullerene solid-state mixtures as active semiconductor layer and poly-vinyl-alcohol (PVA) or divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) as gate dielectrics are presented. With LiF/A1 top source-drain contacts all devices show dominantly n-type transistor behaviour. Devices fabricated with PVA as gate insulator reveal gate voltage induced saturation upon illumination but low photostability. Contrary, devices fabricated with BCB as gate insulator show transistor amplification in a wide range of illumination intensities. The increase of the drain-source current by more than two orders of magnitudes upon illumination is explained by the generation of a large carrier concentration due to photoinduced charge transfer at the conjugated polymer/fullerene bulk heterojunction upon illumination (photodoping). After illumination, a change of the dark transfer characteristics with respect to the initial transfer characteristics was observed. The initial dark state is achieved either by applying a large negative gate bias or by annealing. (c) 2006 Elsevier B.V. All rights reserved.