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.

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.