Molecular understanding of π-conjugated polymer/solid-state ionic liquid complex as a highly sensitive and selective gas sensor

An electric-field driven chemical doping modulation in a blend of solution-processed organic semiconductors (OSC) and solid-state ionic liquids (SSIL) in response to volatile organic compounds (VOC) provides a new exciting opportunity to facilitate printable and low-power chemical gas sensors (chemiresistors). In order to fully exploit this opportunity, fundamental understanding of the molecular-level interactions among the OSC, SSIL, and VOC components during device operation is urgently needed. Herein, we demonstrate a highly sensitive and selective VOC gas sensor using π-conjugated polymer (here, P3HT as a model homopolymer) and SSIL blends. A newly developed SSIL forms a semi-crystalline solid at room temperature. High molecular weight and high regioregularity P3HT allows an extremely well-interconnected network in blends desirable for efficient charge transport. In P3HT/SSIL blends, we identify electric-field driven strong chemical interactions between π-CP and SSIL to tune electrical conductivity of π-CPs. The enlarged interfacial areas in blends and the solid-state nature of SSIL ensure highly tuneable electrochemical interactions between them, efficiently modulating π-CPs’ electrical conductivity further upon exposure to different polar and non-polar VOCs. Our results demonstrate the π-conjugated polymer/SSIL complex as a new highly sensitive and selective gas sensor and provide a key scientific understanding of its molecular-level operational mechanism critical for developing molecular sensors towards next generation noninvasive diagnostics.