Precise Control Light Emission of PVDF-CH₃NH₃PbBr_3-xCl_x Nanocrystalline Films Using a Cl^-(CH₃OH)_n System

Methylammonium lead halide perovskites with highly efficient pure-color or white-light generation have gained increasing scientific interest and promote the development of a great commercial opportunity in displays, lighting, and other applications. However, the poor stabilities, lead toxicity, and unfriendly solvents and ligands in the growth process severely restrict their commercial application. Here, we proposed a green method for preparing uniform and stable polymer-encapsulated photoluminescence (PL) tunable CH₃NH₃PbBr_3-xCl_x NC thin films at room temperature. Utilizing the swelling effect between alcohol compounds and organic polymers and the ionization of NaCl in methanol solution, the anion exchange process can be achieved rapidly within 7 min. Moreover, the PL wavelengths of the CH₃NH₃PbBr_3-xCl_x NCs films were precisely tuned with steps as fine as 2 nm. Experimental results showed that NaCl dissolved in methanol solution can form Cl^-(CH₃OH)_n, which brings ionized Cl into the polymer-encapsulated CH₃NH₃PbBr₃ NCs film for CH₃NH₃PbBr_3-xCl_x NCs film growth. Based on the swelling and anion exchange dynamics, a modified NaCl-CH₃OH-MABr solution system was developed to trigger CH₃NH₃PbBr_3-xCl_x NCs film PL emission tuning from 528 to 463 nm with several-fold intensity enhancement. The realization of precisely controlled photoluminescence from the perovskite nanocrystal film would have wide applications in the optical and imaging fields.