Large‐Area Bi ₂ O ₂ Se Nanosheets With Enhanced Optoelectronic Performance for Flexible Electronics

The rapid progress of flexible electronics demands materials that simultaneously offer outstanding electrical and optoelectronic performance with mechanical durability. Bismuth oxyselenide (Bi 2 O 2 Se) has emerged as a promising candidate due to its high carrier mobility and excellent optoelectronic properties. However, realizing large‐area, high‐quality Bi 2 O 2 Se nanosheets suitable for device fabrication remains a challenge, as conventional low‐pressure chemical vapor deposition (LPCVD) offers limited scalability and narrow growth conditions. This study presents the synthesis of millimeter‐scale Bi 2 O 2 Se nanosheets using atmospheric pressure chemical vapor deposition (APCVD), achieving domain sizes up to 0.4 mm. Systematic investigation of the growth parameters and mechanisms accompanied by COMSOL simulations to study the adatom diffusion on the substrate surface reveals the key factors that enable such large‐domain formation. The resulting nanosheets exhibit excellent electronic transport properties, with average carrier mobilities of 110 cm 2 V −1 s −1 at room temperature and more than 3700 cm 2 V −1 s −1 at 2.3 K. Devices fabricated on flexible substrates maintain stable performance under repeated mechanical bending, underscoring their robustness and durability. These results establish APCVD‐grown Bi 2 O 2 Se as a scalable platform for next‐generation flexible electronic and optoelectronic technologies.