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The effects of molecular packing on the field-effect mobility and external quantum efficiency of polymer light-emitting transistors based on films composed of a donor–acceptor polymer, poly(9,9-dioctylfluorene- al t-benzothiadiazole) (F8BT), are investigated. The molecular packing structures of F8BT films are modified by annealing at different temperatures, such that large grains in a mesophase are formed. In the case of F8BT films in the mesophase, highly crystalline three-dimensional configurations with adjacent chains result in effective electron transport. The electron mobility, μ e , in a device in which the F8BT film is in the mesophase is approximately ten times greater than that for F8BT films annealed at other temperatures, and is estimated to be approximately 3.4 × 10 −3 cm 2 V −1 s −1 . This same device exhibits the highest hole and electron mobilities along with the highest maximum external quantum efficiency (approximately 1.4%) due to improved electron transport and carrier balance. [ABSTRACT FROM AUTHOR]

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: In order to obtain phosphorescent emission from organic field-effect transistors, thermal diffusion of a phosphorescent dye at the interface between the active layer and gate insulator was controlled by utilizing the fact that liquid-crystalline semiconducting polymers self-organize due to reorientation of the molecules and increase in the size of the crystalline regions during thermal annealing. For top-gate type devices using poly(alkylfluorene) doped with a red emissive phosphorescent material, ambipolar characteristics and red emission from the phosphorescent material were clearly observed. We demonstrate the possibility of producing phosphorescent organic light-emitting transistors using a liquid-crystalline semiconducting polymer doped with phosphorescent emissive dopants by the thermal diffusion method. [Copyright &y& Elsevier]

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]