High-Performance, Flexible NO₂ Chemiresistors Achieved by Design of Imine-Incorporated n-Type Conjugated Polymers

Flexible and mechanically robust gas sensors are the key technologies for wearable and implantable electronics. Herein, the authors demonstrate the high-performance, flexible nitrogen dioxide (NO₂ ) chemiresistors using a series of n-type conjugated polymers (CPs: PNDIT2/IM-x) and a polymer dopant (poly(ethyleneimine), PEI). Imine double bonds (C = N) are incorporated into the backbones of the CPs with different imine contents (x) to facilitate strong and selective interactions with NO₂ . The PEI provides doping stability, enhanced electrical conductivity, and flexibility. As a result, the NO₂ sensors with PNDIT2/IM-0.1 and PEI (1:1 by weight ratio) exhibit outstanding sensing performances, such as excellent sensitivity (ΔR/R_b = 240% @ 1 ppm), ultralow detection limit (0.1 ppm), high selectivity (ΔR/R_b < 8% @ 1 ppm of interfering analytes), and high stability, thereby outperforming other state-of-the-art CP-based chemiresistors. Furthermore, the thin film of PNDIT2/IM-0.1 and PEI blend is stretchable and mechanically robust, providing excellent flexibility to the NO₂ sensors. Our study contributes to the rational design of high-performance flexible gas sensors.