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ReviewJ. Jpn. Soc. Colour Mater., 96〔4〕，141–146（2023）

Synthesis and Optical Properties of Water-Durable Lead Halide Perovskite Nanocrystals
Norio Saito＊,†＊Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae, Kofu, Yamanashi 400-8511, Japan†Corresponding Author, E-mail: n-saito@yamanashi.ac.jp(Received November 30, 2022; Accepted February 1, 2023 )Abstract
Metal halide perovskite nanocrystals (MHP NCs) show promise as next-generation optical and electronic materials. Surface passivation ofMHP NCs to improve polar solvent stability is essential for exploiting their optoelectronic properties. Our group sought to develop novelsurface modification methods to improve the chemical and dispersion stabilities of MHP NCs. This short review summarizes our recent
reports on the synthesis and optical properties of lead-based perovskite CsPbBr3 NCs passivated with a cationic oligomeric (gemini, 12-n-12;trimeric, 12-n-12-n-12 ) ligand. Dynamic light scattering experiments revealed excellent dispersion properties following surface passivation
using 12-n-12 ligands with longer spacer groups more than hexylmethylene; other ligands allowed aggregation and precipitation ofnanoparticles. Fluorescence spectroscopy showed that CsPbBr 3 NCs passivated with 12-n-12 had fluorescence efficiency comparable tothat of didodecyldimethylammonium bromide (DDAB), and that they exhibited water stability. We also elucidated the surface chemistry ofCsPbBr 3 NCs passivated with the oligomeric ligands using hard X-ray photoemission spectroscopy (HAXPES).
Key-words: Perovskite, Nanocrystal, Luminescence, Water durability, Ligands

1．Introduction
Organic-inorganic hybrid crystals featuring intriguing
optoelectronic properties and compositional modularity are
emerging replacements for traditional ceramics in functional
materials. In particular, metal halide perovskites (MHPs) 1-3 )with the general formula of ABX 3 (A is a monovalent cation,
B is a divalent cation, and X is a halogen anion) demonstrate
exceptional optoelectronics. MHPs offer excellent lightabsorption, band gap tunability, intriguing excitation
behavior, and efficient photoluminescence quantum yields( PLQYs) . 4 , 5 ) In addition, MHPs can crystallize readily
from solution under ordinary temperatures 6 ) to form bulk
single crystals, 7 ) thin films, 8,9 ) and colloidal nanocrystals(NCs). 10-12 ) Near-unity PLQYs of MHP NC light emitters 13 )foreshadowed advances in various photophysical fields, suchas color filters for light-emitting diodes (LEDs), 14 ) lasers, 15 )photovoltaics, 16 ) and photocatalysis. 17 )〔氏名〕 さいとう のりお〔現職〕 山梨大学大学院総合研究部附属クリスタル科学研究センター 助教〔趣味〕 マラソン，サイクリング，動画編集〔経歴〕 2017 年東京工業大学博士後期課程修了。博士（工学）。同年物質・材料研究機構電子セラミックスグループポスドク研究員。2018年 東 京 理 科 大 学 工 学 部 工 業 化 学 科 助 教。
2022 年より現職。

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Colloidal nanoparticle surface chemistry can control
their photophysical properties, dispersion, and chemical
stability, because of their large surface area-to-volume ratios.
X or A-type ions dissociate from strongly ionic MHP NC
surfaces to yield ionic defects 18 ) responsible for excited statedeactivation. In addition, strong surface ionicity promotes
the incorporation of strongly polar solvent molecules suchas water, 19 ) dimethylformamide (DMF), 20 ) and dimethyl
sulfoxide (DMSO ), 20 ) which decompose the perovskite
three-dimensional framework.
To passivate surface defects and prevent the decompositionof MHP NCs, various types of surface modifications havebeen investigated. 18 ) Our group also investigated new
surface modification methods applicable to lead-based halide
perovskite (e.g., CsPbX 3 and (CH 3 NH 3 )PbX 3 , X = Cl, Br, I)
NCs and recently reported some successful results from theviewpoint of the surface and ligand chemistry. 21,22 ) In thismanuscript, we overview our recent studies on the synthesis
and properties of polar- and water-durable colloidal MHP
NCs, particularly focusing on the ligand chemistry-based
approach.

2．Surface modification of MHP NCs
2.1 Ligand exchange
Fig. 1 shows the origin of the surface defects in MHP
NCs with the general formula ABX 3 and their passivation
with surface-capping ligand molecules. The major origin ofthe surface defects in MHP NCs is assumed to be the ionicvacancies formed by the dissociation of the A- and X-sites,18)－15－© 2023 Journal of the Japan Society of Colour Material