Interfacial Engineering of PdSe ₂ /GaSe Heterostructures for Applications as a Light-Activated Ultrafast NO ₂ Sensor at Room Temperature

Achieving rapid recovery kinetics in room-temperature (RT) gas sensors remains a bottleneck for practical environmental monitoring. Herein, we demonstrate a high-performance NO 2 sensor based on the n -PdSe 2 / p -GaSe vertical heterojunction, precisely assembled via a dry-transfer technique. Under 405 nm illumination, the nanodevice exhibits exceptional sensing properties at RT, featuring ultrafast response and recovery times of 25 and 82 s, respectively─a remarkable enhancement compared to its dark-state performance. Beyond its fast-response characteristics, the sensor maintains high selectivity toward NO 2 against common interfering gases and reliable long-term stability. Mechanistically, in situ Kelvin probe force microscopy (KPFM) revealed a 23 mV surface potential change upon NO 2 exposure, providing direct spatial evidence of work-function modulation and a downward Fermi-level shift, consistent with NO 2 -induced p -type doping. This phenomenon underscores a synergistic interplay between the p–n junction’s built-in field and photoexcited carrier dynamics, which effectively suppresses the activation energy barrier for gas–solid interactions at the nanomaterial interface, thereby markedly expediting NO 2 adsorption/desorption kinetics. This work highlights the efficacy of interfacial barrier engineering in 2D nanostructures, offering a promising strategy for the realization of ultrafast, room-temperature, and energy-efficient optoelectronic gas-sensing technologies.