In-situ fabricated anisotropic halide perovskite nanocrystals in polyvinylalcohol nanofibers : Shape tuning and polarized emission

We report an in-situ fabrication of halide perovskite (CH₃NH₃PbX₃, CH₃NH₃ = methylammonium, MA, X= Cl, Br, I) nanocrystals in polyvinylalcohol (PVA) nanofibers (MAPbX₃@PVA nanofibers) through electrospinning a perovskite precursor solution. With the content of the precursors increased, the resulting MAPbBr₃ nanocrystals in PVA matrix changed the shape from ellipsoidal to pearl-like, and finely into rods-like. Optimized MAPbBr₃@PVA nanofibers show strong polarized emission with the photoluminescence quantum yield of up to 72%. We reveal correlations between the shape of in-situ fabricated perovskite nanocrystals and the polarization degree of their emission by comparing experimental data from the single nanofiber measurements with theoretical calculations. Polarized emission of MAPbBr₃@PVA nanofibers can be attributed to the dielectric confinement and quantum confinement effects. Moreover, nanofibers can be efficiently aligned by using parallel positioned conductor strips with an air gap as collector. A polarization ratio of 0.42 was achieved for the films of well-aligned MAPbBr₃@PVA nanofibers with a macroscale size of 0.5 cm x 2 cm, which allows potential applications in displays, lasers, waveguides, etc.