Australian Centre for Advanced Photovoltaics, School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia.
Centre for Micro-Photonics, Swinburne University of Technology, Melbourne, Victoria 3122, Australia.
Nat Commun. 2017 Jan 20;8:14120. doi: 10.1038/ncomms14120.
The hot-phonon bottleneck effect in lead-halide perovskites (APbX) prolongs the cooling period of hot charge carriers, an effect that could be used in the next-generation photovoltaics devices. Using ultrafast optical characterization and first-principle calculations, four kinds of lead-halide perovskites (A=FA/MA/Cs, X=I/Br) are compared in this study to reveal the carrier-phonon dynamics within. Here we show a stronger phonon bottleneck effect in hybrid perovskites than in their inorganic counterparts. Compared with the caesium-based system, a 10 times slower carrier-phonon relaxation rate is observed in FAPbI. The up-conversion of low-energy phonons is proposed to be responsible for the bottleneck effect. The presence of organic cations introduces overlapping phonon branches and facilitates the up-transition of low-energy modes. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material also increases the overall up-conversion efficiency. This result also suggests a new and general method for achieving long-lived hot carriers in materials.
卤铅钙钛矿（APbX）中的热声子瓶颈效应延长了热载流子的冷却时间，这一效应可用于下一代光伏器件中。本研究采用超快光学特性和第一性原理计算，对四种卤铅钙钛矿（A=FA/MA/Cs，X=I/Br）进行了比较，以揭示其内部的载流子-声子动力学。结果表明，混合钙钛矿中的声子瓶颈效应强于其无机对应物。与基于铯的系统相比，在 FAPbI 中观察到载流子-声子弛豫速率慢 10 倍。提出低能声子的上转换是导致瓶颈效应的原因。有机阳离子的存在引入了重叠的声子支，促进了低能模式的上跃迁。与材料极低热导率相关的声子传播阻断也增加了整体上转换效率。该结果还为在材料中实现长寿命热载流子提供了一种新的通用方法。
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