Intermediate Phase Halide Exchange Strategy toward a High-Quality, Thick CsPbBr₃ Film for Optoelectronic Applications

Inorganic halide perovskite CsPbBr₃ is emerging as one of the promising alternatives to the hybrid counterparts for optoelectronic applications owing to its upgraded stability. Yet, the inherently low solubility of a CsBr precursor material restricts the quality and especially the thickness of a solution-processed CsPbBr₃ film, thus hindering the further optimization of device performance. Herein, we report a facile intermediate phase halide exchange reaction that can break the thickness limit of a solution-processed CsPbBr₃ film, since it avoids the use of low-solubility CsBr. Furthermore, the CH₃NH₃I byproduct after halide exchange could trigger a beneficial Ostwald ripening process to promote grain coarsening in the film. Hence, the uniformly flat, pure-phase, and compact CsPbBr₃ film composed of [100] preferential, microsized grains can be achieved. As a demonstration of its excellent optoelectronic features, the carbon-based, all-inorganic photodetector with such a favorable film yields a maximum photoresponsivity of 0.35 A W^-1 and a specific detectivity of 1.94 × 10¹³ Jones coupled with a response time of 0.58 μs.