Effects of film morphology on ambipolar transport of top- gate-type polymer light-emitting transistors utilizing ambipolar polymer-blend films

The effects of film morphology on ambipolar transport of top-gate-type polymer light-emitting transistors utilizing blended fluorene-type polymers of poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) were investigated. All devices based on ambipolar polymer-blend films with various blend ratios as the active layer exhibited the ambipolar and light-emitting characteristics. The morphology of blended films changed markedly with the blend ratio and annealing temperature. Hole mobilities of the devices with F8:F8BT blended films are independent of film morphology. The difference of behavior of electron mobility in the F8:F8BT devices resulted from the major morphological differences of surface structure that the channel can be considered to be formed. F8BT molecules in F8 act as electron trap sites owing to the wide gap between F8 and F8BT LUMO levels.