Self-stratified semiconductor/dielectric polymer blends: vertical phase separation for facile fabrication of organic transistors

Abstract

Semiconducting/insulating polymer blends are promising materials for use in organic thin film transistor (OTFT) applications. Here, vertically phase-separated poly(3-hexylthiophene) (P3HT)-top and poly(methyl methacrylate) (PMMA)-bottom blend films were developed for the facile fabrication of OTFTs with excellent electrical properties. The microstructures of the blend films could be adjusted simply by altering the film processing conditions, which impacted the electrical properties of the OTFTs based on the blend films. A decrease in the P3HT content of the blend film significantly reduced the interface roughness between the semiconductor (P3HT) and dielectric (PMMA) layers, which reduced charge trapping or scattering, thereby increasing the field-effect mobility. A higher solution concentration tended to increase the drying time during film deposition, which allowed the P3HT molecules to self-organize over a long period of time. This led to an increase in the ordering of the phase-separated P3HT film, which significantly improved the device performance. TFTs based on a P3HT/PMMA (1/39 w/w) film prepared from a 4 wt% blend solution showed the best field-effect performance with a saturated field-effect mobility of 0.022 cm² V⁻¹ s⁻¹ and an I_on/I_off current ratio of 2 × 10⁵. The vertically stratified P3HT/PMMA films were also suitable for the fabrication of all-polymer TFT devices on flexible substrates.