open access

https://doi.org/10.14943/doctoral.k15137

https://hdl.handle.net/2115/90557

ハロゲン化物ペロブスカイト膜と単一粒子における光誘起電子移動と励起子ダイナミクスの研究

英語

2022-09-26

Hokkaido University

ix, 119p.

Lead halide perovskites have become the most promising semiconductor materials for light-harvesting and light-emitting applications. These materials in the nanocrystalline forms, obtained by reliable colloidal synthesis approaches, show high photoluminescence quantum yield, high charge carrier mobilities, long photoluminescence lifetimes, and high photostability. However, their exciton, charge carrier properties, and interfacial electron transfer dynamics need optimization for next-generation perovskite devices. This thesis mainly focuses on the electron donor-acceptor systems involving perovskite nanocrystal films or single-particles, including the exciton, charge carrier, and electron-transfer dynamics. It is summarized in five chapters. In chapter 1, I discuss the general properties and significance of lead halide perovskites. First, I introduce their structure, chemical compositions, and stability factors. Subsequently, I explain various perovskite nanocrystal synthesis methods to control the shape and dimensionality. The preparation methods for self-assembled perovskite nanocrystal thin films and different characterization techniques are discussed in the second section of this chapter. In the third section, I present the bandgap and fundamental optical properties of perovskite nanomaterials as functions of their halogen compositions, size, and shape. Also, I describe the charge carrier properties and quantum confinement in perovskite nanocrystals and films. In the final section, I explain the applications of halide perovskites to solar cells, photodetectors, and light-emitting diodes, summarizing my research motivation and objectives. In chapter 2, I provided complete details about the materials, synthesis methods, samples, and instrumentation techniques in this thesis. Perovskite nanocrystals are synthesized using hot injection, ligand-assisted reprecipitation, and a modified spray technique. Next, I explain the theoretical bases, working principles, and instrumental setups of various spectroscopic (UV-vis absorption, steady-state and time-resolved fluorescence spectroscopy, and transient absorption spectroscopy) and microscopic (single-particle fluorescence microscopy, transmission electron microscopy, and scanning electron microscopy) techniques. In chapter 3, I summarize the extent of carrier diffusion, the degree of radiative loss, and the rate of diffusion-controlled interfacial electron transfer in heterojunction films of cesium or formamidinium lead bromide nanocrystals and C60 or TiO2. Electron transfer and charge separation were confirmed by measuring the photoluminescence decays, intensities, and transient absorption spectra. By measuring the distance-dependent photoluminescence lifetimes and photocounts in samples containing halide perovskite-C60 or halide perovskite-TiO2 donor-acceptor junctions, I find long-range (>100 μm) carrier diffusion and distance-dependent (>800 μm) interfacial electron transfer. In chapter 4, I demonstrate the electron transfer dynamics at the single-particle level by analyzing the photoluminescence blinking of single perovskite nanocrystals with or without tetracyanoquinodimethane or tetracyanobenzene. The Gibbs free energy changes of electron transfer are estimated to be negative, using the donors and acceptors' redox potentials and the HOMO-LUMO gaps/bandgaps. The electron transfer rates are determined from time-resolved photoluminescence measurements. Further, the statistical analysis of >450 single perovskite nanocrystals and the ON-time and OFF-time probability distributions help understand the photoluminescence blinking to the electron transfer relationship. In chapter 5, I investigated exciton-plasmon interactions for perovskite nanocrystals on Au plasmonic nanogaps. I find a huge photoluminescence intensity enhancement for perovskite single nanoparticles directly synthesized in Au nanogaps. Here, the Au nanogaps are created by the controlled Au sputter-coating on glass substrates, followed by the spray-synthesis of perovskite nanocrystals on the Au-coated substrates. The radiative exciton recombination rate of perovskite nanocrystals in the Au substrate is dramatically increased by coupling with the localized surface plasmon, obvious from a drastic decrease in the photoluminescence lifetime and an increase in the photocounts. The increased radiative recombination rate is attributed to the chemical and electromagnetic coupling of the Au plasmon with perovskite nanocrystals. Finally, I summarize the thesis and provide the prospect of the work embodied in this thesis.

2022-09-26

甲第15137号

博士(環境科学)

(主査) 教授 BIJU VASUDEVAN PILLAI, 教授 中村 貴義, 教授 八木 一三

環境科学院（環境物質科学専攻）

博士論文

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