Enabling multidimensional fine-tuning of large-sized BiOI films using ultrasonic spray pyrolysis

Bismuth oxyiodide (BiOI) has emerged as a prominent oxide semiconductor for applications in optoelectronic conversion and energy catalysis. However, the fabrication of uniform, tunable, and large-sized BiOI thin films remains challenging, limiting their versatility across diverse application scenarios. Ultrasonic spray pyrolysis (USP) deposition offers inherent scalability for thin-film production, yet its practical application is hindered by a limited mechanistic understanding and the absence of multidimensional control strategies. In this study, we elucidate the deposition mechanism of BiOI via USP and develop comprehensive methods for its multidimensional control, achieving modulation of the growth orientation, size and thickness of the BiOI nanoflakes and the uniformity of BiOI films. Notably, BiOI photoelectrodes with a (102) orientation exhibited exceptional photoelectrochemical performance. Through optimized spraying conditions, we successfully fabricated a uniform large-area BiOI film measuring 25 × 25 cm² for the first time. Furthermore, utilizing BiOI as an intermediate template, we transformed its morphology into Bi₂O₃ and BiFeO₃, paving the way for intermediate conversion methods of bismuth-based materials. This study advances the mechanistic understanding of BiOI growth via USP and establishes a multidimensional approach for the scalable synthesis of BiOI, thereby expanding the potential applications of large-area bismuth-based materials in energy and optoelectronic technologies.