Star polymer–TiO2 nanohybrids to effectively modify the surface of PMMA dielectric layers for solution processable OFETs

Abstract

Solution processable dielectric nanomaterials were prepared by the polymer-templated synthesis of hybrid nanoparticles containing TiO₂. Well defined poly(styrene-co-acrylonitrile)-b-poly(acrylic acid)-poly(divinylbenzene) (PSAN-b-PAA-PDVB) star-shaped copolymers were prepared using activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and then used as templates for the synthesis of nanoconfined TiO₂. Unexpectedly, even very low inorganic loadings significantly modified the surface of the poly(methyl methacrylate), (PMMA), layers. Relatively thick (with a thickness of 0.6 μm, affordable for the inkjet printing method) PMMA layers comprising merely 0.4% wt. of the hybrid TiO₂ nanoparticles were applied as gate dielectrics for organic field effect transistors (OFETs). Such a low content of hybrid nanoparticles, which essentially did not affect the dielectric properties of the PMMA layer, significantly improved the efficiency of the obtained OFETs, as compared with OFETs based on pure PMMA as gate dielectrics, e.g. charge carrier mobility has increased nearly 10-fold from ca. 0.06 to ca. 0.5 cm² V⁻¹ s⁻¹. The improvement of OFET parameters may be explained by a significant decrease of roughness (root mean square roughness of the dielectric layer was reduced from 15.3 nm to 0.43 nm) and change of surface energy (from 32.4 to 45.5 mN m⁻¹) of the gate dielectric layer induced by hybrid nanoparticles. OFETs with novel dielectric layers showed current–voltage characteristics with high drain currents and negligible hysteresis. The presented results showed that the physicochemical properties of the surface of the polymer layer may be easily modified by the addition of small amounts of new hybrid nanoparticles.