Balancing Surface Hydrophobicity and Polarizability of Fluorinated Dielectrics for Organic Field‐Effect Transistors with Excellent Gate‐Bias Stability and Mobility

Abstract

It is demonstrated that treating dielectrics with fluorinated polymers, which have excellent hydrophobicity, chemical inertness, and the lowest polarizability, yields a semiconductor‐compatible surface energy and excellent charge detrapping characteristics. Fluorocopolymers, polystyrene‐ random ‐poly(2,3,4,5,6‐pentafluorostyrene) (PS‐ r ‐PPFS) copolymers with different 2,3,4,5,6‐pentafluorostyrene (PFS) loadings, are synthesized to modify a SiO 2 gate dielectric using radical polymerization. Surface energy ( γ ) of the copolymer‐treated SiO 2 dielectrics decreases from 40.7 to 24.0 mJ m −2 with increasing PFS mol% in the copolymer. Pentacene organic field‐effect transistors (OFETs) show field‐effect mobility ( μ FET ) values ranging from 0.82 (for 0 mol% PFS) to 0.25 cm 2 V −1 s −1 (for 100 mol% PFS). Enhancing the bias stress stability without affecting the μ FET value is achieved via the introduction of a small mol% fluorocarbon segments onto the PS‐ r ‐PPFS backbone. 15 mol% PFS‐loaded fluorocopolymer‐coated SiO 2 substrate yields a γ value of 35 mJ m −2 , close to that (38 mJ m −2 ) of the lowest‐ γ crystal surface of pentacene, and the corresponding OFETs have μ FET values up to 0.81 cm 2 V −1 s −1 and excellent gate‐bias stress stability in comparison to the rich fluorinated dielectric systems, which has degraded μ FET values ranging from 0.2 to 0.4 cm 2 V −1 s −1 .