Using thin film transistors to quantify carrier transport properties of amorphous organic semiconductors

The hole transport properties of two phenylamine-based compounds were evaluated by thin film transistor (TFT) measurement and time-of-flight (TOF) technique. The compounds were N, N′ -diphenyl- N, N′ -bis(1-naphthyl) (1, 1′ biphenyl) -4, 4′ diamine (NPB) and 4, 4′, 4″ -tris[n-(2-naphthyl)-n-phenyl-amino] triphenylamine (2TNATA). With tungsten oxide/gold as the charge injecting electrode, the field effect mobility of NPB was found to be 2.4× 10-5 cm2 V s at room temperature, which was about one order of magnitude smaller than that obtained from independent TOF experiments (3× 10-4 cm2 V s). Similar observations were found for 2TNATA. Temperature dependent measurements were carried out to study the energetic disorder of the materials. It was found that the energetic disorder was increased in the neighborhood of a gate dielectric layer.