Dielectric Screening Enabled Ultrastable Luminescence in CsPbBr3 Perovskite Crystal Encapsulated by Ferroelectric Poly(vinylidene fluoride)

Metal halide perovskites nanocrystals (NCs) are emerging as competitive alternatives for semiconductor NCs in the fields of consumer optoelectronic devices; however, boosting their long-term stability still needs extensive study. Encapsulation of perovskite NCs with polymer becomes a promising strategy, yet the dielectric screening effect on the excitons of perovskites from the polymer matrix has seldom been considered. Here, we demonstrated this effect in high-permittivity poly(vinylidene fluoride) (PVDF) encapsulated CsPbBr3 (CPB) crystals CPB/PVDF composites films. The in situ nonuniform growth mechanism of CPB crystal with respect to its concentration in the precursor was revealed from multiscale structure observations. Comprehensive physical properties of CPB/PVDF composites with varying CPB concentrations were thoroughly investigated. Composite films made from precursors with CPB concentration increasing to saturation all showed bright luminescence, and an exceptional long fluorescence lifetime up to tau(avg) = 731 ns was observed, much superior to other polymers with lower permittivity encapsulated CPB composites. The stable luminescence is understood from the strong interplay between electron-hole Coulomb interactions in CPB and its surrounding high-permittivity PVDF. Meanwhile, the interfacial interaction between CPB and PVDF greatly influenced the crystallization behavior of PVDF polymer at nanoscale, thus altered the dielectric and mechanical properties of CPB/PVDF composite films accordingly. Finally, a warm white light-emitting diode device was assembled based on green light emitting CPB/PVDF film, positively implying its potential application in high-performance optoelectronic devices.