Organic field-effect transistor and its photoresponse using a benzo[1,2-b: 4,5-b′] difuran-based donor-acceptor conjugated polymer

Organic field-effect transistors (OFETs) were fabricated through a solution process with a donor-acceptor (D-A) conjugated polymer poly{4,8-bis(2'-ethylhexylthiophene) benzo [ 1,2-b; 3,4-b'] difuran-alt-5,5-(4',7'-di-2-thienyl- 5',6'-dioctyloxy-2',1',3'-benzothiadiazole)} (PBDFTDTBT) as the active layer, which is a highly efficient D-A conjugated polymer as a donor in polymer solar cells with a power conversion efficiency (PCE) over 6.0%. The OFET devices showed a hole mobility of 0.05 cm(2)/Vs and an on/off ratio of 4.6 x 10(5). Those are one of the best performance parameters for OFETs based on wD-A conjugated polymers including benzo[ 1,2-b: 4,5-b'] dithiophene (BDT) or benzo[ 1,2-b: 4,5-b'] difuran (BDF) unit. The photoresponse of OFETs was investigated by modulating light with various intensities. The devices produced a photosensitivity (I-light/I-dark) of 1.2 x 10(5) and a photoresponsivity of 360 mAW (1) under white light illumination. The drain current in saturation region increases gradually with increasing illumination intensity. The threshold voltage exhibited a positive shift from -15.6 V in darkness to 27.8 V under illumination, which can be attributed to the well-known photovoltaic effect resulting from the transport of photogenerated holes and trapping of photogenerated electrons near the source electrode in organic phototransistors. Meanwhile, the devices showed good stability and with no obvious degeneration for 3 months in air. The study suggests that D-A conjugated polymers including BDF unit can be potentially applied in OFETs and organic phototransistors in addition to highly efficient polymer solar cells. (C) 2014 Elsevier B.V. All rights reserved.