Dual‐Photosensitizer Synergy Empowers Ambient Light Photoactivation of Indium Oxide for High‐Performance NO₂ Sensing

Abstract Light‐activated chemiresistors offer a powerful approach to achieving lower‐temperature gas sensing with unprecedented sensitivities. However, an incomplete understanding of how photoexcited charge carriers enhance sensitivity obstructs the rational design of high‐performance sensors, impeding the practical utilization under commonly accessible light sources instead of ultraviolet or higher‐energy sources. Here, a rational approach is presented to modulate the electronic properties of the parent metal oxide phase, exemplified by this model system of Bi‐doped In₂O₃ nanofibers decorated with Au nanoparticles (NPs) that exhibit superior NO₂ sensing performance. Bi doping introduces mid‐gap energy levels into In₂O₃, promoting photoactivation even under visible blue light. Additionally, green‐absorbing plasmonic Au NPs facilitate electron transfer across the heterojunction, extending the photoactive region toward the green light. It is revealed that the direct involvement of photogenerated charge carriers in gas adsorption and desorption processes is pivotal for enhancing gas sensing performance. Owing to the synergistic interplay between the Bi dopants and the Au NPs, the Au‐Bi_xIn_2‐xO₃ (x = 0.04) sensing layers attain impressive response values (R_g/R_a = 104 at 0.6 ppm NO₂) under green light illumination and demonstrate practical viability through evaluation under simulated mixed‐light conditions, all of which significantly outperforms previously reported visible light‐activated NO₂ sensors.