Energy Frontiers Research Center for Excitonics, ‡Department of Physics, §Department of Chemical Engineering, ∥Department of Chemistry, and ⊥Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
Nano Lett. 2014 Jun 11;14(6):3556-62. doi: 10.1021/nl501190s. Epub 2014 May 13.
Colloidal quantum dots (QDs) are promising materials for use in solar cells, light-emitting diodes, lasers, and photodetectors, but the mechanism and length of exciton transport in QD materials is not well understood. We use time-resolved optical microscopy to spatially visualize exciton transport in CdSe/ZnCdS core/shell QD assemblies. We find that the exciton diffusion length, which exceeds 30 nm in some cases, can be tuned by adjusting the inorganic shell thickness and organic ligand length, offering a powerful strategy for controlling exciton movement. Moreover, we show experimentally and through kinetic Monte Carlo simulations that exciton diffusion in QD solids does not occur by a random-walk process; instead, energetic disorder within the inhomogeneously broadened ensemble causes the exciton diffusivity to decrease over time. These findings reveal new insights into exciton dynamics in disordered systems and demonstrate the flexibility of QD materials for photonic and optoelectronic applications.
胶体量子点 (QDs) 是在太阳能电池、发光二极管、激光和光电探测器中应用的有前途的材料，但 QD 材料中激子输运的机制和长度还不是很清楚。我们使用时间分辨光学显微镜来空间可视化 CdSe/ZnCdS 核/壳 QD 组装体中的激子输运。我们发现，激子扩散长度可以通过调整无机壳层厚度和有机配体长度进行调节，在某些情况下超过 30nm，这为控制激子运动提供了一种强大的策略。此外，我们通过实验和动力学蒙特卡罗模拟表明，QD 固体中的激子扩散不是通过随机行走过程发生的；相反，不均匀展宽的激子在各向同性的能带上的扩散导致激子扩散率随时间降低。这些发现揭示了无序系统中激子动力学的新见解，并展示了 QD 材料在光子学和光电应用中的灵活性。
