Gate-voltage-dependent charge transport in multi-dispersed polymer thin films

In semiconductor polymers, charge transport usually occurs via hopping between localized states, which are generally multi-dispersed due to multi-dispersed chemical structures, crystallinities, and phase segregations. We report a combined modeling and experimental study to investigate gate-voltage-dependent charge transport in field-effect transistors based on multi-dispersed polymers including semiconductor:semiconductor and semiconductor:insulator blends. Film-depth-dependent charge accumulation and transport are correlated with vertical composition profiles and film-depth-dependent energetic distribution of localized states. Even low gate-voltage could accumulate charges in any depth of the films, greatly increasing charge density in some (sub-) components for effective charge transport. Therefore, neither overall high crystallinity nor molecular ordering near the semiconductor-dielectric interface is necessarily required for high field-effect mobility (μ_FET). This study not only proposes a model for high effective μ_FET recently reported in some nearly amorphous polymer films and the “bislope feature” in their transfer characteristics but also helps improve transistor performances and exploit transistor operations via manipulating charge distribution in multi-dispersed films.