Phase Separation of P3HT/PMMA Blend Film for Forming Semiconducting and Dielectric Layers in Organic Thin-Film Transistors for High-Sensitivity NO₂ Detection

Formation of the semiconductor/dielectric double-layered films via vertical phase separations from polymer blends is an effective method to fabricate organic thin-film transistors (OTFTs). Here, we introduce a simple one-step processing method for the vertical phase separation of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends in OTFTs and their applications for high-performance nitrogen dioxide (NO2) sensors. Compared to the conventional two-step coated OTFT sensors, one-step processed devices exhibit a great enhancement of the responsivity from 116 to 1481% for 30 ppm NO2 concentration and a limit of detection of ∼0.7 ppb. Studies of the microstructures of the blend films and the electrical properties of the sensors reveal that the devices formed by the one-step vertical phase separation have better capability for the adsorption of NO2 molecules. Moreover, a careful adjustment of the blend ratio between P3HT and PMMA can further improve the performance of the NO2 sensors, ranging from sensitivity to selectivity and to the ability of recovery. This simple one-step processing method demonstrates a potential possibility for developing high-performance, low-cost, and large-area OTFT gas sensors.