PVDF-directed synthesis, stability and anion exchange of cesium lead bromide nanocrystals

Photoluminescent perovskite nanocrystals are mostly used along with base materials such as polymers for material processing and large-scale production purpose. However, the role of polymer in crystal structure engineering and thereby dictating the emission properties of lead halide perovskite nanocrystals has been poorly understood. First, we have developed a polymer-directed antisolvent method for synthesis of halide perovskite crystals at room temperature and observed that the thermodynamic stabilities of crystals drive the formation of perovskite composite crystal of orthorhombic Cs₄PbBr₆and monoclinic CsPbBr₃. Surprisingly, hydrophobic polyvinylidene fluoride (PVDF) can reduce the size of perovskite crystals to nano dimensions even at room temperature. On the other hand, perovskite nanocrystals, CsPbBr₃synthesized by modified hot-injection method undergo rapid encapsulation in PVDF matrices. The size of the encapsulated nanocrystal in PVDF matrices ranges in 88 ± 32 nm. We have illustrated that there are three types of radiative recombination predominantly operative in nanocrystals-doped polymer- (i) surface defect caused radiative recombination (0.6-3 ns), (ii) exciton recombination (3-15 ns), and (iii) shallow trap assisted recombination (10-50 ns). The interface created at nanocrystal and polymer plays a decisive role in populating the shallow trap states in perovskite-polymer nanocomposite. These nanocomposites undergo fast halide exchange in aqueous hydroiodic acid solution and possess remarkable enhancement of water-/photo-stability. This research would pave way for their greater use in hydrogen production and light-emitting devices.