Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Am Chem Soc. 2010 Apr 7;132(13):4858-64. doi: 10.1021/ja100106z.
Multiexciton generation in quantum dots (QDs) may provide a new approach for improving the solar-to-electric power conversion efficiency in QD-based solar cells. However, it remains unclear how to extract these excitons before the ultrafast exciton-exciton annihilation process. In this study we investigate multiexciton dissociation dynamics in CdSe QDs adsorbed with methylene blue (MB(+)) molecules by transient absorption spectroscopy. We show that excitons in QDs dissociate by ultrafast electron transfer to MB(+) with an average time constant of approximately 2 ps. The charge separated state is long-lived (>1 ns), and the charge recombination rate increases with the number of dissociated excitons. Up to three MB(+) molecules per QD can be reduced by exciton dissociation. Our result demonstrates that ultrafast interfacial charge separation can effectively compete with exciton-exciton annihilation, providing a viable approach for utilizing short-lived multiple excitons in QDs.
多激子的产生在量子点（QD）中可能提供一种新的方法来提高基于 QD 的太阳能电池的太阳能到电能的转换效率。然而，在超快激子-激子湮灭过程之前，如何提取这些激子仍然不清楚。在这项研究中，我们通过瞬态吸收光谱研究了吸附有亚甲基蓝（MB(+)）分子的 CdSe QD 中的多激子离解动力学。我们表明，QD 中的激子通过超快电子转移到 MB(+)上离解，平均时间常数约为 2 ps。电荷分离态的寿命很长（>1 ns），并且电荷复合速率随离解激子的数量增加而增加。通过激子离解可以还原一个 QD 中的多达三个 MB(+)分子。我们的结果表明，超快界面电荷分离可以有效地与激子-激子湮灭竞争，为利用 QD 中的短寿命多激子提供了一种可行的方法。
