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

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-pentafl uorostyrene (PFS) loadings, are synthesized to modify a SiO2 gate dielectric using radical polymerization. Surface energy (gamma) of the copolymer-treated SiO2 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 (mu(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 mu 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 SiO2 substrate yields a. value of 35 mJ m(-2), close to that (38 mJ m(-2)) of the lowest-gamma crystal surface of pentacene, and the corresponding OFETs have mu(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 mu(FET) values ranging from 0.2 to 0.4 cm(2) V-1 s(-1).