Synergetic effect of electrochemical doping and long-range charge transport in solution-processed organic/inorganic hybrid chemiresistors for ultrasensitive NO2 detection

• A hybrid approach combines polymer electrolytes, solid-state ionic liquids (SILs) and 2D MXene for ultrasensitive NO 2 detection. • SILs enable molecular-level electrochemial doping, while MXene supports long-range charge transport at low bias and room temperature. • Chemiresistors based on the hybrid system achieve high sensitivity (ΔR/R 0 = 48 % at 10 ppm) and ultralow detection limit (∼53 ppb). • The chemiresistors also demonstrate excellent reliability over 1000 bending cycles, promising flexible sensing applications. Molecular-level electrochemical doping of solution-processed conjugated polymers (CPs) with solid-state ionic liquids (SILs) has emerged as a key technology for obtaining highly selective and sensitive chemiresistors. However, their responsivity and signal-to-noise ratio (SNR) still need to be significantly improved before commercialization. Herein, we demonstrate highly selective, sensitive, and flexible organic/inorganic hybrid chemiresistors for nitrogen dioxide (NO 2 ) detection, exploiting the synergetic effects of: 1) the electrochemical doping of a polymer electrolyte by a SIL, and 2) the long-range charge transport by a two-dimensional (2D) MXene. The SIL with a long alkyl chain enables the molecular-level electrochemical doping of the polymer electrolyte, while the 2D MXene provides a long-range charge transport pathway, facilitating the operation of the device under low-bias conditions (≤ 1 V). Notably, during NO 2 exposure, additional electrochemical doping can be selectively and sensitively carried out in the hybrid chemiresistors owing to the presence of [NO 2 ] − anions. Therefore, the hybrid chemiresistors exhibit outstanding sensing capabilities, including an excellent sensitivity (Δ R / R 0 = 48 % at 10 ppm) and ultralow limit of detection (∼ 53 ppb). Based on the excellent reliability of the hybrid chemiresistor over 1000 bending cycles, our approach shows promising potential for achieving stable electrochemical reactions in emerging flexible sensing technologies.