2019 Fiscal Year Annual Research Report
Defect-free, Highly-luminescent and Non-blinking Perovskite Nanocrystals
| Project/Area Number |
19H02550
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| Research Institution | Hokkaido University |
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Principal Investigator |
Biju V・Pillai 北海道大学, 電子科学研究所, 教授 (60392651)
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | Lead halide perovskites / Perovskite nanocrystals / Perovskite quantum dots / Perovskite microcrystals / Photoluminescence / Electroluminescence / Blinking / Defect passivation |
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| Outline of Annual Research Achievements |
Microcrystals (MCs), nanocrystals (NCs) and quantum dots (QDs) of lead halide perovskites with different photoluminescence (PL) color were synthesized. Also, their PL and electroluminescence (EL) properties were studied at the ensemble solution phase and single particle levels. The synthesis of rod- and cube-shaped MCs was carried out by the inverse temperature crystallization method, anti-solvent-assisted crystallization method, or laser trapping crystallization method. These MCs are methylammonium lead halide (MAPbX3; X=Cl, Br or I), and methylammonium lead mixed-halides. The synthesis of NCs or QDs were carried out by the hot injection method or ligand-assisted crystallization method. These NCs and QDs are formamidinium lead bromide (FAPbBr3), MAPbX3, and cesium lead bromide (CsPbBr3). The PL color of MCs and NCs were tuned in the blue-green-red region by the controlled exchange of halide ions. Also, the PL intensity of the crystals were improved by the halide exchange and halide saturation. The as synthesized NCs and QDs samples showed PL quantum yield (QY) as high as 60 to 80%, suggesting the presence of 40 to 20% defects. The PLQY was improved to 90 to 98% by the passivation of defects with halide donors and using controlled amounts of ligands, which also resulted in an increase in the PL lifetime of the samples. Also, the defects in the as synthesized NCs and QDs were obvious from PL and EL blinking in single particle PL studies. Such a blinking was removed by the passivation of defects and the suppression of the reaction of oxygen with the defects.
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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
The materials planned in this project were a few types of defect-free lead halide perovskite (LHP) nanocrystals (NCs). Also, the suppression of blinking by the evaluation and passivation of defects was another goal of the proposal. However, different synthesis methods were applied to various combinations of LHP precursors, which helped with the preparation of LHP microcrystals (MCs), NCs and quantum dots (QDs) with different compositions, sizes, and bandgaps. Importantly, a completely novel method for laser induced synthesis as well as bandgap tuning of different LHPs was demonstrated. This synthesis and bandgap tuning were beyond the expectations. Also, with the optimization of ligands on the surface of LHP NCs, this project demonstrated the controlled assembling of LHP NCs for light emitting devices (LEDs), which is an unexpected achievement. A patent application is filed on ligand-controlled assemblies of LHP NCs for LEDs. Yet another unexpected achievement is the development of highly photoluminescent LHPs with multicolor emission. Thus, in addition to the proposed preparation of defect-free LHP NCs and the passivation of defects in NCs, this project advanced beyond the plans by the development of (i) LHP MCs, NCs and QDs with multicolor emission, (ii) a new laser-induced synthesis method for LHP, and (iii) the ligand-assisted LHP assemblies for LEDs.
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| Strategy for Future Research Activity |
Towards the proposed plans, research in this year will be focused on the surface passivation of lead halide perovskite (LHP) nanocrystals (NCs) such as CsPbBr3, FAPbBr3, and MAPbI3 NCs, which will be carried out by doping LHPs with cations and electron donors. The effects of these passivating agents on the photoluminescence (PL) quantum yield (QY), PL lifetime and blinking of LHP NCs will be investigated by the ensemble and single-particle studies. Thus, as proposed, this project will continue to focus on the development of defect-free LHP NCs with high PL QYs, less blinking, and high stability. Furthermore, this research will focus on the electroluminescence (EL) properties of LHPs by focusing the research on the improvement of EL QY and suppression of EL blinking.
In addition to the development of the above LHP NCs, research in the past year helped with the development of LHP microcrystals (MCs) and quantum dots (QDs) with different PL color. LHP MCs were synthesized by a laser trapping method and LHP QDs were synthesized by the colloidal methods. This year, a part of the effort will be focused on the optimization of PL QY and bandgaps of these MCs and QDs. Also, the PL blinking of QDs and EL blinking of MCs will be studied and suppressed.
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