Lead halide perovskite semiconductors have been studied intensively with respect to application as active layers in solar cells and light-emitting diodes, because of their excellent optoelectronic properties. Particularly, the solution-based synthesis method that became available for this material class, offers a cost-effective production of photonic devices with high-performance owing to a direct band-gap with strong radiative band-to-band recombination, a high crystal quality with extremely low defect/trap densities, and photon recycling [1-3]. In addition to solution-based growth of thin films and single crystals, colloidal synthesis enables preparation of novel perovskite nanocrystals. Their experimentally verified high photoluminescence quantum yields and wavelength-tunable luminescence that covers the entire visible spectrum make them promising candidates for light-emitting diodes, lasers, and single photon sources. A detailed knowledge about the exciton dynamics in single nanocrystals is essential to design such new devices. Here, we summarize optical properties of organic-inorganic hybrid perovskite FAPbBr3 and all-inorganic halide perovskite CsPbBr3 nanocrystals. Their exciton dynamics were studied by femtosecond transient-absorption and single-dot spectroscopy. From the simultaneous measurement of the second-order photon correlation g(2) and photoluminescence-decay curves of single nanocrystals , we evaluated the luminescence quantum yields of biexcitons. The exciton and charged-exciton lifetimes were determined as a function of the absorption cross-section of the single nanocrystals. We discuss the characteristic decay dynamics of excitons, charged excitons, and biexcitons in lead halide perovskite nanocrystals [5,6].
The author would like to thank many colleagues and his students for their contributions and discussions. Part of this work was supported by JST-CREST (Grant No. JPMJCR16N3).
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