open access

https://doi.org/10.14943/doctoral.k16235

https://hdl.handle.net/2115/97669

ハロゲン化物ペロブスカイト系における励起子の再結合、移動、および転移の探求

英語

2025-03-25

Hokkaido University

xiv, 133p.

Lead halide perovskites have emerged as promising semiconductors for a broad spectrum of applications, such as solar cells, lasers, light-emitting diodes, and photodetectors. Their prominence stems from their outstanding characteristics, including facile synthesis, strong light absorption capabilities, tunable bandgaps, and exceptional charge carrier mobility. Bulk perovskite has a high carrier diffusion length, making it promising for optoelectronic applications. However, it is difficult to fabricate into a thin film which is necessary for increasing device performance. In contrast, a perovskite nanocrystal (PNC) film can be easily fabricated with a desired thickness. However, these PNCs often face instability due to defects, low carrier diffusion due to high quantum confinement, and reduced carrier extraction at the interface, hindering their overall efficiency. The basic aim of this thesis is to improve the stability of PNCs through defect passivation, enhance carrier diffusion via assembly formation, and increase carrier extraction into the transport layers using multiwall carbon nanotubes (MWCNTs) as acceptors. The thesis is structured into five chapters. Chapter 1 provides an introduction to perovskites, focusing on their structures, photoluminescence (PL) behavior, and carrier diffusion dynamics across different perovskite sample types. Special emphasis is placed on the use of PNC films with an optimal thickness to maximize carrier diffusion. This chapter also explores various carrier extraction strategies and potential applications of perovskites. Chapter 2 details the synthesis methodologies for PNCs and perovskite quantum dots (PQDs) using the hot-injection method. The functionalization process of MWCNTs is also detailed here. It also includes microscopic and spectroscopic tools, such as steady-state absorption spectroscopy, steady-state fluorescence spectroscopy, time-resolved single-photon counting, transient absorption spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning transmission electron microscopy, and single-particle microscopy. Chapter 3 focuses on the defect passivation of CsPbBr3 PNCs, which is mainly responsible for the nonradiative recombination and instability. STEM-EDX analysis of CsPbBr3 PNCs synthesized using the hot injection method reveals the presence of Br ? vacancies, leading to a low PL quantum yield (QY) and a short PL lifetime. The PNCs were post-treated with various inorganic halide sources including CsBr, NaBr, and KBr. PLQY, PL lifetime, and intensity trajectories after vacancy filling were measured. Among various halide salts I tested for defect passivation, NaBr was identified as the most effective, increasing the PLQY from 58% to 98%. The PL lifetime also increases from 11.6 ns to 13.8 ns. Single-particle blinking studies show that suppressed blinking supports the vacancy filling in CsPbBr3 PNCs. Defect passivation significantly reduces nonradiative recombination, improving the photophysical properties of the PNCs. For a longer carrier diffusion length, assembly formation of low dimensional perovskite is necessary. In Chapter 4, I demonstrated the polymer-induced assembly formation of FAPbBr3 PQDs. The solvent evaporation and polybutadiene polymer shrinkage during drying help to assemble the PQDs within a polymer, resulting in a redshifted PL spectral maximum and a longer PL lifetime. This can be attributed to the wave function overlap of the PQDs and miniband formation. Temperature-controlled carrier diffusion was also demonstrated in this chapter. An increase in the temperature of the assembly resulted in a PL spectral blueshift and lifetime decrease, both indicating thermal dissociation of the assembly. Cooling the assembly to room temperature partially restored the optoelectronic properties. These findings underscore the potential of such assemblies for use in optoelectronic devices responsive to external stimuli. Although increased carrier diffusion helps the carrier to reach the charge transport layer, interfacial electronic coupling, and carrier transportation to the electron and hole transport layers are critical for accomplishing efficient carrier extraction. In Chapter 5, I focus on the rapid extraction of charge carriers from CsPbBr3 PNCs using MWCNTs as the electron acceptor layer. The MWCNTs were first functionalized with terminal phenylamine groups to facilitate binding with the PNCs. PNC-MWCNT interface samples were prepared using both post-mixing and in situ hot-injection methods. The resulting PNC-MWCNT conjugates exhibit hot-carrier transfer from the PNCs to the MWCNTs, a reduction in biexciton-mediated nonradiative Auger recombination, and reduced radiative recombination at the band edge. Overall, this thesis outlines methods to enhance PNC quality through halide vacancy filling, enhance the diffusion or transportation of photogenerated charge carriers through assemblies, and extract the carriers across PNC-MWCNT interfaces by hot-electron transfer. These improvements are beneficial for developing more efficient and durable optoelectronic devices.

2025-03-25

甲第16235号

博士(環境科学)

(主査) 教授 Biju Vasudevan Pillai, 教授 小西 克明, 准教授 髙野 勇太

環境科学院（環境物質科学専攻）

博士論文

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