Cesium-based perovskite nanocrystals (PNCs) possess alluring optical and electronic properties via compositional and structural versatility, tunable bandgap, high photoluminescence quantum yield and facile chemical synthesis. Despite the recent progress, origins of the photoluminescence emission in various types of PNCs remains unclear. Here, we study the photon emission from individual three-dimensional and zero-dimensional cesium lead bromide PNCs. Using photon antibunching and lifetime measurements, we demonstrate that emission statistics of both type of PNCs are akin to individual molecular fluorophores, rather than traditional semiconductor quantum dots. Aided by density functional modelling, we provide compelling evidence that green emission in zero-dimensional PNCs stems from exciton recombination at bromide vacancy centres within lead-halide octahedra, unrelated to external confinement. These findings provide key information about the nature of defect formation and the origin of emission in cesium lead halide perovskite materials, which foster their utilization in the emerging optoelectronic applications.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was financially supported by King Abdullah University of Science and Technology (KAUST). Y.Z. is grateful to the seeding fund from University of Jinan, China. Work of UT Dallas group (T.G., R.B. and A.V.M.) was supported by U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-SC0010697. A.V.M. gratefully acknowledges travel support from CRDF Global at early stages of the work. We thank Dr. J.A. Hollingsworth from Los Alamos National Lab for CdSe/CdS samples.