Yu Buyang, Chen Lan, Qu Zhengkang, Zhang Chunfeng, Qin Zhengyuan, Wang Xiaoyong, Xiao Min
National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China.
Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States.
J Phys Chem Lett. 2021 Jan 14;12(1):238-244. doi: 10.1021/acs.jpclett.0c03350. Epub 2020 Dec 16.
The lifetimes of hot carriers have been predicted to be prolonged in small nanocrystals with an inter-level spacing larger than phonon energy. Nevertheless, whether such a phonon bottleneck is present in perovskite semiconductor nanocrystals remains highly controversial. Here we report compelling evidence of a phonon bottleneck in CsPbI nanocrystals with marked size-dependent relaxation of hot carriers by using broadband two-dimensional electronic spectroscopy (2DES). By combining high resolutions in both the time (<10 fs) and excitation energy domains, 2DES allows the clear disentanglement of the thermalization and cooling processes. The lifetime is over doubled for hot carriers when the average edge length of the nanocrystals decreases from 8.2 nm down to 4.6 nm. The confirmation of the phonon bottleneck effect suggests the feasibility of controlling hot carrier dynamics in perovskite semiconductors with nanocrystal size for potential applications of hot carrier devices.
据预测，在能级间距大于声子能量的小纳米晶体中，热载流子的寿命会延长。然而，钙钛矿半导体纳米晶体中是否存在这种声子瓶颈仍然存在很大争议。在此，我们通过使用宽带二维电子光谱（2DES）报告了CsPbI纳米晶体中声子瓶颈的有力证据，其中热载流子具有明显的尺寸依赖性弛豫。通过在时间（<10 fs）和激发能域都具有高分辨率，2DES能够清晰地区分热化和冷却过程。当纳米晶体的平均边长从8.2 nm减小到4.6 nm时，热载流子的寿命增加了一倍多。声子瓶颈效应的证实表明，通过控制纳米晶体尺寸来控制钙钛矿半导体中的热载流子动力学，对于热载流子器件的潜在应用是可行的。
