Dual-Phase CsPbCl₃-Cs₄PbCl₆ Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl₃-Cs₄PbCl₆ films. It is achieved by spin-coating of a certain dose of CH₃NH₃Cl/CsCl solution onto a CsI-PbBr₂-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl₃-Cs₄PbCl₆ film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl₃-Cs₄PbCl₆ film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W^-1, an exceptional specific detectivity (D*) maximum of 1.35 × 10¹² Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.