Nakazawa Naoki, Zhang Yaohong, Liu Feng, Ding Chao, Hori Kanae, Toyoda Taro, Yao Yingfang, Zhou Yong, Hayase Shuzi, Wang Ruixiang, Zou Zhigang, Shen Qing
Faculty of Informatics and Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan.
Nanoscale Horiz. 2019 Mar 1;4(2):445-451. doi: 10.1039/c8nh00341f. Epub 2018 Dec 4.
Understanding the behaviour of multiple exciton dissociation in quantum dot (QD) solid films is of fundamental interest and paramount importance for improving the performance of quantum dot solar cells (QDSCs). Unfortunately, the charge transfer behaviour of photogenerated multiple exciton in QD solid films is not clear to date. Herein, we systematically investigate the multiple exciton charge transfer behaviour in PbS QD solid films by using ultrafast transient absorption spectroscopy. We observe that the multiple exciton charge transfer rate within QD ensembles is exponentially enhanced as the interparticle distance between the QDs decreases. Biexciton and triexciton dissociation between adjacent QDs occurs via a charge transfer tunneling effect just like single exciton, and the charge tunneling constants of the single exciton (β: 0.67 ± 0.02 nm), biexciton (β: 0.68 ± 0.05 nm) and triexciton (β: 0.71 ± 0.01 nm) are obtained. More importantly, for the first time, the interparticle distance limit (≤4.3 nm) for multiple exciton charge transfer between adjacent QDs is found for the extraction of multiple excitons rapidly before the occurrence of Auger recombination. This result points out a vital and necessary condition for the use of multiple excitons produced in PbS QD films, especially for their applications in QDSCs.
了解量子点（QD）固体薄膜中多激子解离行为对于改善量子点太阳能电池（QDSCs）的性能具有根本意义且至关重要。遗憾的是，迄今为止，量子点固体薄膜中光生多激子的电荷转移行为尚不清楚。在此，我们通过超快瞬态吸收光谱系统地研究了PbS量子点固体薄膜中的多激子电荷转移行为。我们观察到，随着量子点之间的粒子间距减小，量子点集合体内的多激子电荷转移速率呈指数增强。相邻量子点之间的双激子和三激子解离通过电荷转移隧穿效应发生，就像单激子一样，并且获得了单激子（β：0.67±0.02 nm）、双激子（β：0.68±0.05 nm）和三激子（β：0.71±0.01 nm）的电荷隧穿常数。更重要的是，首次发现了相邻量子点之间多激子电荷转移的粒子间距限制（≤4.3 nm），以便在俄歇复合发生之前快速提取多激子。这一结果指出了使用PbS量子点薄膜中产生的多激子的一个至关重要且必要的条件，特别是对于它们在量子点太阳能电池中的应用。
