A thin-film transistor, such as a top-gate thin-film transistor, is provided herein. The thin-film transistor has a performance-enhancing layer, such as a performance-enhancing bottom layer, comprising a polymer other than a polyimide. In specific embodiments, the polymer is selected from the group consisting of polysiloxane, polysilsesquioxane, and mixtures thereof. In other embodiments, it is a self-assembling polymeric monolayer of a silane agent and an organophosphonic acid. The performance-enhancing layer directly contacts the substrate. The layer improves the carrier mobility and current on/off ratio of the thin film transistor.