Self-Assembled Lead Halide Perovskite Nanocrystals in a Perovskite Matrix

Abstract

Hybrid metal halide perovskite materials are produced with facile routes, but their morphology is sensitive to water, oxygen, temperature, and exposure to light. While phase separation and self-assembly of perovskite nanostructures have been demonstrated, the realization of controlled perovskite–perovskite heterostructures has been limited up to now. We demonstrate here the growth of stable CH3NH3PbI3–xBrx nanocrystals in a CH3NH3PbBr3 matrix. Optical emission from the nanocrystals can be reversibly activated upon illumination through a photobrightening process. Optical microscopy images show that nanocrystals are stable in time, through several illumination cycles. Ultrafast photoluminescence measurements imply that optical excitations are funneled from the matrix into the lower bandgap nanocrystals. Because the nanocrystals represent <2% of the materials volume, the local carrier concentration is higher in the nanocrystals than in the matrix, leading to an increase in the photoluminescence quantum yield, highlighting the promise of such self-assembled heterostructures for efficient light-emitting device

Perovskite Excitonics: Primary Exciton Creation and Crossover from Free Carriers to a Secondary Exciton Phase

“…Trap saturation strategies may allow longer excited state lifetime and therefore more time for exciton formation . Quantum confinement strategies on the other hand may produce materials with increased exciton formation rates, such as 2D layered perovskite materials, dot‐in‐matrix or nanocrystalline composites, by enhancing the exciton binding energy E b , and therefore the Langevin coefficient B L which is proportional to E b , and at the same time increase local concentration by funnelling optical excitations …”

Phase Stability and Diffusion in Lateral Heterostructures of Methyl Ammonium Lead Halide Perovskites

“…Hysteresis in the current-voltage characteristics of solar cells is attributed to halide migration. 18,19 Mixed bromide-iodide perovskites can phase separate into I-rich and Brrich domains upon light exposure, [20][21][22][23][24][25][26][27][28][29][30][31] leading to instabilities in the performance of Br-rich perovskite solar cells. [32][33][34][35][36][37] A thorough understanding of halide movement in mixed-halide perovskites is therefore desirable for future design of efficient devices.…”

“…While much progress has been made towards understanding the mechanisms and kinetics of light-induced phase separation, [20][21][22][23][24][25][26][27][28][29][30][31] the diffusion of halides in MAPb(BrxI1−x)3 without illumination is not as well understood. Many studies have focused on ion/vacancy movement in response to an electric field, 18,38-48 rather than on ion/vacancy movement down a concentration gradient.…”

“…Despite the success of alloys, halides can diffuse in hybrid perovskites, which negatively impacts the performance of devices. Hysteresis in the current–voltage characteristics of solar cells is attributed to halide migration. , Mixed bromide–iodide perovskites can phase-separate into I-rich and Br-rich domains upon light exposure, − leading to instabilities in the performance of Br-rich perovskite solar cells. − A thorough understanding of halide movement in mixed halide perovskites is therefore desirable for future design of efficient devices.…”

Single-crystalline hybrid halide perovskites : heterostructure growth and electroluminescence characteristics

“…The mixed halide materials where two halide ions are in a perovskite structure also pose a stability concern related to phases segregation which creates more stable forms such as lead halide (PbX2) triggered by external sources such as light or heat [65,66].…”