Composition‐Dependent Hot Carrier Relaxation Dynamics in Cesium Lead Halide (CsPbX3, X=Br and I) Perovskite Nanocrystals
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Abstract Cesium‐based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot‐carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot‐carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs‐based perovskite (CsPbX 3 with X=Br, I, or their mixtures) NCs on the hot‐carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot‐carrier relaxation dynamics with following order: CsPbBr 3 (310 fs)>CsPbBr 1.5 I 1.5 (380 fs)>CsPbI 3 NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI 3 NC compared to CsPbBr 3 NC.Keywords:
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Organo-lead halide perovskites (OHPs) have recently emerged as a new class of exceptional optoelectronic materials, which has been used in many applications, including solar cells, light emitting diodes, and photodetectors. However, despite the thorough studies into lead halide perovskites during over past 10 years, there are still many unknowns concerning both the device performance and the stability, which are strongly related to their crystal quality as well as their optoelectronic properties. This thesis reports on the study of perovskite crystal growth and the mechanism of light induced phase segregation and ion migration in mixed halide perovskite materials.
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Halide perovskite nanocrystals have attracted more and more attention, because of their facile synthesis and outstanding optical and electronic properties. It has been shown that the halide perovskite nanocrystals exhibit size-dependent optical and electric properties distinct from their bulk counterparts due to strong quantum confinement effects. In this chapter, the recent development of synthesis methods of halide perovskite nanocrystals is first introduced, and the photophysics of halide perovskite nanocrystals such as exciton generation and charge extraction as well as the strategy to improve the quality of halide perovskite nanocrystals are well summarized and discussed. Finally, the application of halide perovskite nanocrystals in solar cells field is deeply discussed.
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The performance of perovskite solar cells is strongly influenced by the composition and microstructure of the perovskite. A recent approach to improve the power conversion efficiencies utilized mixed-halide perovskites, but the halide ions and their roles were not directly studied. Unraveling their precise location in the perovskite layer is of paramount importance. Here, we investigated four different perovskites by using X-ray photoelectron spectroscopy, and found that among the three studied mixed-halide perovskites, CH3 NH3 Pb(I0.74 Br0.26 )3 and CH3 NH3 PbBr3-x Clx show peaks that unambiguously demonstrate the presence of iodide and bromide in the former, and bromide and chloride in the latter. The CH3 NH3 PbI3-x Clx perovskite shows anomalous behavior, the iodide content far outweighs that of the chloride; a small proportion of chloride, in all likelihood, resides deep within the TiO2 /absorber layer. Our study reveals that there are many distinguishable structural differences between these perovskites, and that these directly impact the photovoltaic performances.
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Abstract Despite the exciting progress on power conversion efficiencies, the commercialization of the emerging lead (Pb) halide perovskite solar cell technology still faces significant challenges, one of which is the inclusion of toxic Pb. Searching for Pb‐free perovskite solar cell absorbers is currently an attractive research direction. The approaches used for and the consequences of Pb replacement are reviewed herein. Reviews on the theoretical understanding of the electronic, optical, and defect properties of Pb and Pb‐free halide perovskites and perovskite derivatives are provided, as well as the experimental results available in the literature. The theoretical understanding explains well why Pb halide perovskites exhibit superior photovoltaic properties, but Pb‐free perovskites and perovskite derivatives do not.
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Lead bromide perovskite nanoparticles are fabricated in the water, which has been recognized previously as a severe source of damage to halide perovskite materials and devices. The perovskite nanoparticles exhibit a high photoluminescence quantum yield and excellent material stability.
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Organolead-halide-perovskite-based solar cells have recently received significant attention due to their excellent photovoltaic performance and low cost. The general formula of this perovskite light harvester is RPbX3, where R and X stand for a monovalent organic cation and halide anion, respectively. Structures of the perovskite solar cell are designed based on the function of the perovskite. Organolead halide perovskites can be used either as sensitizers or n- or p-type light harvesters. Rapid progress has been made over the past year since the first report on long-term, durable, 9.7% efficiency perovskite solar cells based on CH3NH3PbI3-sensitized TiO2 in 2012. As a result, power conversion efficiencies as high as 16% have been achieved. Further improvement is expected from this material in terms of understanding charge accumulation and transport properties. Organolead halide perovskite is now regarded as a promising solar cell material, opening new horizons in solar cell research.
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