Effects of molecular packing on the field-effect mobility and external quantum efficiency of ambipolar polymer light-emitting transistors incorporating a donor–acceptor polymer.

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]