Field-effect bulk mobilities in polymer semiconductor films measured by sourcemeters

Semiconducting polymers inherently exhibit polydispersity in terms of molecular structure and microscopic morphology, which often results in a broad distribution of energy levels for localized electronic states. Therefore, the bulk charge mobility strongly depends on the free charge density. In this study, we propose a method to measure the charge-density-dependent bulk mobility of conjugated polymer films with widely spread localized states using a conventional field-effect transistor configuration. The gate-induced variation of bulk charge density typically ranges within ±1018 cm−3; however, this range depends significantly on the energetic dispersion width of localized states. The field-effect bulk mobility and field-effect mobility near the semiconductor–dielectric interface along with their dependence on charge density can be simultaneously extracted from the transistor characteristics using various gate voltage ranges.