| Outline of Annual Research Achievements |
The research focused on defect passivation of lead halide perovskite nanocrystals (PNCs), quantum dots (PQDs), and microcrystals (PMCs), to develop defect-free LHPs. In this project, cesium (Cs)-, formamidinium (FA)-, and methylammonium (MA) lead bromide and iodide PNCs, PQDs, and PMCs with the visible-to-near infrared emission were synthesized by solution processing (colloidal synthesis), laser trapping (spatiotemporally controlled synthesis), or inverse temperature crystallization. The as-synthesized PNCs, PQDs, and PMCs showed short photoluminescence (PL) lifetimes, low PL intensities, and intense PL blinking. These poor characteristics are attributed mainly to ionic defects, forming deep traps in the bandgap and promoting nonradiative exciton recombination. Thus, this research focussed on the halide defect filling in PNCs, PQDs, and PMCs. Halide defect filling was carried out in single PNCs, single PQDs, and single PMCs by observing the PL lifetime, PL intensity, and PL blinking in real-time. The defect filling in single PNCs and PQDs provided PL quantum efficiency as high as 96% with near-complete blinking suppression. The defect filling in PMCs increased the PL lifetime and intensity, which further helped engineer the bandgap in perovskites. Thus, this research progressed to the realization of defect filling in halide perovskites and achievement of perovskite NCs, PQDs, and PMCs with longer PL lifetimes and higher PL intensities, or better quantum efficiencies than the as-synthesized halide perovskites.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
This research planned to develop defect-free, nonblinking lead halide perovskite nanocrystals (PNCs). In addition to the blinking suppression in real-time in PNCs, this research expanded to the controlled defect filling in microcrystals (PMCs) and quantum dots (PQDs), which suppressed the nonradiative recombination in PNCs, PQDs, and PMCs. Thus, photoluminescence (PL) lifetimes and intensities of these materials were enormously increased. Further, the defect filling helped us locally control halide exchange and bandgap engineering of PMCs. Also, this research progressed from the PL optimization to electroluminescence at the single-particle level. Thus, the studies progressed to results beyond the initial planning.
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| Strategy for Future Research Activity |
The plans include photoluminescence (PL) and electroluminescence (EL) optimization of halide perovskite structures such as quantum dots, platelets, nanocrystals, microplates, microcubes, and microrods. Here, the optimization will be by halide vacancy filling and in the presence of electron donors or acceptors. For this purpose, the above perovskite structures will be synthesized by solution processing. Then, single-particle and ensemble PL and EL studies will be conducted as functions of the defect density, defect filling, and electron donor/acceptor density. Further, SEM-EDX will be used for evaluating the defect filling. Halide defect density, electron transfer rate, PL blinking, and PL lifetime will be compared and optimized.
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