Ultrastable Photoactive Halide Perovskite Nanocrystal‐Sensitized SnO ₂ Nanorods for Room‐Temperature NO ₂ Detection

ABSTRACT Metal oxide (MO x )‐based NO 2 gas sensors typically require high temperatures or ultraviolet light, limiting their practical use. To enable visible‐light activation at room temperature, efficient and stable photosensitizers should be integrated with nanostructured MO x hosts. Halide perovskites (HP) have gained attention as promising visible‐light photosensitizers due to their excellent optoelectronic properties. However, the structural stability of HP remains a critical barrier to practical implementation, necessitating robust passivation strategies that ensure both long‐term durability and efficient interfacial charge transport. Herein, we present a novel strategy in which CsPbBr 3 nanocrystals (NCs) are encapsulated with an ultra‐thin (∼2 nm) SiO 2 shell and integrated onto structurally engineered porous SnO 2 nanorods (NRs). The sensor exhibits 13‐fold and 30‐fold enhancement in response to 10 ppm NO 2 gas under green light, compared to dark conditions and planar SnO 2 , respectively. Furthermore, the SiO 2 encapsulation enables the CsPbBr 3 NCs to maintain long‐term stability as photosensitizers for over 5 weeks, which is an unprecedented duration among visible light‐activated gas sensors. Our results demonstrate the synergistic effect of surface defect passivation and nanostructure engineering, providing a robust design strategy for realizing highly stable and high‐performance gas sensors based on HP photosensitizers and nanostructured MO x hosts under visible light.