Improvement of the chemical and physical gas adsorption ability of poly(3-hexylthiophene) thin films by ultraviolet-ozone exposure

Abstract

Organic semiconductors are emerging as replacements for inorganic semiconductors, which are too rigid and heavy to be utilized in next-generation devices such as electronic skins (e-skins). However, organic sensors display a lower reactivity and selectivity with target gases than inorganic semiconductor-based gas sensors. In particular, organic sensors face critical limitations in that they have low charge density and surface energy. To address these limitations, we applied ultraviolet-ozone (UV-O₃) treatment to modify the surface of poly(3-hexylthiophene) (P3HT) thin films with the aim of enhancing their gas-sensing performance. Among the gas sensor devices, the P3HT sensor treated with UV-O₃ for 30 s exhibited remarkable sensing characteristics, achieving a sensitivity of 1.5%/ppm and a limit of detection of 21.5 ppb for NO₂ gas. The UV-O₃ treatment induces two primary effects: oxidation of the polymer surface and etching of the polymer chains. These changes have a profound impact on the P3HT film's physical and chemical properties. The oxidation and chain scission of the P3HT film induced by UV-O₃ increased the hydrophilicity and free volume of the active layer. These modifications were observed to enhance the sensitivity and selectivity of the sensor toward NO₂ gas by improving the interaction between gas molecules and the permeability in the channel region.