NO2-Affinitive Amorphous Conjugated Polymer for Field-Effect Transistor Sensor toward Improved NO2 Detection Capability

Abstract

Three conjugated polymers (CPs) containing indolocarbazole-based similar conjugated frameworks are designed to investigate the NO2 detection capability of field-effect transistor (FET) sensors. The partly linear aliphatic side chain strengthens the crystallization tendency of the CPs, but the crystallinity is critically degraded when introducing an ethylene oxide (EO)-modified side chain to the same conjugated framework. Although the highly crystalline morphology of the CP helps to achieve high hole mobility, the NO2 response rate of the CP-based FET sensor is severely deteriorated because of the suppression of NO2 diffusion into the CP matrix. The polar and flexible EO-modified side chain is helpful to improve the NO2-affinity of the CPs and induce favorable pathways for NO2 diffusion, ultimately providing enhanced detectivity with better NO2-response characteristics. As a result, despite low charge carrier mobility due to pure amorphous nature, the CP with EO-modified side chains provides an exceptional sensitivity of 180%/ppm upon NO2 (100 ppb) exposure for 50 s, including distinct detectivity toward other environmentally abundant harmful polar gases, such as SO2, NO, and NH3.