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The influence of ultraviolet (UV) irradiation on carrier conduction and emission characteristic of the top-gate-type ambipolar organic field-effect transistors (OFETs) utilizing crystallized poly(9,9-dioctylfluorene) (F8) films were investigated. For a device with irradiated UV light, only p-type conduction was exhibited and the hole field-effect mobility was almost the same as that without UV irradiation. As a result, the EL emission was not observed owing to the decrease of n-type conduction after UV irradiation. It is suggested that the quenching center which is generated in F8 film by UV irradiation is greatly related to the electron trap site of OFETs. [ABSTRACT FROM PUBLISHER]

Abstract: The effects of film morphology on ambipolar transport in solution-processed top-gate-type organic field-effect transistors (OFETs) utilizing poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) films were investigated. All the F8T2 OFETs without toluene-vapor treatment showed ambipolar characteristics. In contrast, for toluene-vapor-treated F8T2 films at below 250°C, which were observed to have a small fibrillar structure and a large number of grain boundaries, electron conduction decreased remarkably. Structure ordering in F8T2 films has a strong influence on ambipolar charge transport in OFETs. With an increase in the annealing temperature, the electron transport characteristics were improved. Improving the interface geometry of the F8T2 film, which is related with the decrease of grain boundaries, led to an increase in mobility, and the appearance of ambipolar characteristics. These results suggest that the appearance of electron conduction results not only from the increase in grain size but also from improvements in the connections between grain boundaries in F8T2. Ambipolar F8T2 OFETs exhibited yellow EL emissions, hole and electron field-effect mobilities of approximately 10−3 cm2 V−1 s−1, and maximum external quantum efficiency of approximately 0.2%. [Copyright &y& Elsevier]

Abstract: The properties of polymer light-emitting transistors with Ag-nanowire (AgNW) source/drain electrodes fabricated on a polymer substrate are investigated. Organic field-effect transistors (OFETs) based on poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) with AgNW source/drain electrodes exhibit ambipolar characteristics. For an ambipolar F8BT OFET, yellow-green light emission is observed. The maximum external quantum efficiency is 0.6%. We demonstrate the possibility of producing flexible polymer light-emitting transistors using AgNW electrodes. [Copyright &y& Elsevier]

Highlights: [•] Indium tin oxide (ITO) and Ag are used as source/drain (S/D) electrodes. [•] Influence of S/D electrodes on external quantum efficiency (EQE). [•] Exciton quenching by Ag electrodes results in a low EQE. [•] A relatively high EQE of 1% regardless of the emission site for the device with ITO. [•] Lower exciton quenching at the interface of S/D electrodes for the device with ITO. [ABSTRACT FROM AUTHOR]

Abstract: The effects of adding solution-processed polyfluorene derivatives as buffer layers between the polymer insulator and active layer of n-channel organic field-effect transistors (OFETs) containing a carbonyl-bridged bithiazole derivative were investigated. The surface free energy was modified by the polyfluorene derivatives. A poly(9,9-dioctylfluorene) (F8) buffer layer, which has a hydrophobic nature, a low surface free energy, and consists almost entirely of a dispersion component, improved the growth morphology of the OFET active layer. An OFET with an F8 buffer layer exhibited n-channel characteristics, and an electron field-effect mobility of 0.025cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of solution processed top-gate-type organic field-effect transistors (OFETs) with indium–tin oxide (ITO) drain/source electrodes using polyfluorene derivatives were investigated. An OFET with poly(9,9-dioctylfluorene) (F8) as an active layer, which contains only a fluorene backbone, exhibited ambipolar characteristics with hole and electron field-effect mobilities of approximately 10−3 cm2 V−1 s−1. All OFETs with fluorene derivatives exhibited ambipolar characteristics because the value of the work function of the ITO electrode is approximately in the middle between the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of fluorene derivatives. Fluorene derivatives can conduct both holes and electrons. Ambipolar OFETs with F8 and a fluorene derivative doped in F8 can be applied to various color tunable light-emitting devices. [Copyright &y& Elsevier]