Timmerman Dolf, Matsubara Eiichi, Gomez Leyre, Ashida Masaaki, Gregorkiewicz Tom, Fujiwara Yasufumi
Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
National Institute of Technology (KOSEN), Asahikawa College, Shunkodai 2-2-1-6, Asahikawa, Hokkaido 071-8142, Japan.
ACS Omega. 2020 Aug 19;5(34):21506-21512. doi: 10.1021/acsomega.0c02067. eCollection 2020 Sep 1.
Multiple exciton generation (MEG) takes place in competition to other hot carrier cooling processes. While the determination of carrier cooling rates is well established, direct information on MEG dynamics has been lacking. Here, we present a methodology to obtain the MEG rate directly in the initial ultrafast transient absorption dynamics. This method is most effective to systems with slow carrier cooling rates. Perovskite quantum dots exhibit this property and are used to illustrate this approach. They show a delayed carrier concentration buildup following an excitation pulse above the MEG threshold energy, which is accompanied by a faster carrier relaxation, providing a direct evidence of the MEG process. Numerical modeling within a simple framework of two competing cooling mechanisms allows us to extract the MEG rate and carrier energy cooling rates for this material. The presented methodology could provide new insights in carrier generation physics and valuable information for MEG investigations.
多激子产生（MEG）与其他热载流子冷却过程相互竞争。虽然载流子冷却速率的测定已经很成熟，但关于MEG动力学的直接信息一直缺乏。在此，我们提出一种方法，可在初始超快瞬态吸收动力学中直接获得MEG速率。该方法对载流子冷却速率较慢的系统最为有效。钙钛矿量子点具有这一特性，并被用于说明该方法。在高于MEG阈值能量的激发脉冲之后，它们显示出载流子浓度的延迟积累，同时伴随着更快的载流子弛豫，这为MEG过程提供了直接证据。在两种相互竞争的冷却机制的简单框架内进行数值建模，使我们能够提取该材料的MEG速率和载流子能量冷却速率。所提出的方法可为载流子产生物理学提供新的见解，并为MEG研究提供有价值的信息。
