Highly Sensitive Flexible <scp>NO</scp> ₂ Resistive Gas Sensor Based on Polythiophene/Multi‐Walled Carbon Nanotubes/ <scp>SnO</scp> ₂ Ternary Composite

ABSTRACT This study tackles the challenges of low sensitivity and slow response/recovery in polythiophene (PTh)‐based NO 2 sensors by integrating multi‐walled carbon nanotubes (MWCNTs) and tin metal–organic framework (Sn‐MOF)‐derived tin dioxide (SnO 2 ) nanoparticles, resulting in a PTh/MWCNT/SnO 2 ternary composite flexible gas sensor. The composite, prepared via chemical oxidative polymerization, hydrothermal synthesis, and mechanical blending, is fabricated into a multi‐layered sensing structure on a polyimide substrate using flexible electronics printing. Doped with 3% MWCNT and 6% SnO 2 , the sensor significantly outperforms pure PTh. At 150°C, it achieves a 76.8% response to 100 ppm NO 2 , with response/recovery times dramatically reduced to 23 and 75 s, respectively. Simultaneously, the sensor's response to a low concentration of 500 ppb NO 2 was 1.28%. The sensor exhibits excellent NO 2 selectivity (3.9 times higher than for C 3 H 6 O), good repeatability (less than 5% deviation over 8 cycles), and strong long‐term stability (82.4% initial response over 40 days). Mechanistic analysis indicates enhanced performance from a dual approach: p–n heterojunctions optimize interface depletion layer regulation and charge transfer, while the MWCNT's 3D conductive network accelerates electron transport and gas diffusion. This research offers a new avenue for high‐performance, flexible environmental monitoring.