Determination of the density of trap states in organic thin film transistors

Polymer thin-film transistors based on poly(9,9-dioctylfluorene-co- bithiophene) (F8T2) have been studied in the temperature range from 130 to 300K. In this temperature range both the field effect mobility and the drain current show thermally activated behaviour. The channel current at low gate voltage (|Vgs|< |Vth|) can be fitted with a power function of gate voltage. We deduce the presence of an exponential distribution of localized states above the dominant transport level from the gate bias and temperature dependence of the drain current.