Cavendish Laboratory, University of Cambridge, Cambridge, UK.
Department of Emerging Materials Science, DGIST, Daegu, Republic of Korea.
Nat Mater. 2022 May;21(5):533-539. doi: 10.1038/s41563-022-01204-6. Epub 2022 Mar 7.
Quantum dot (QD) solids are an emerging platform for developing a range of optoelectronic devices. Thus, understanding exciton dynamics is essential towards developing and optimizing QD devices. Here, using transient absorption microscopy, we reveal the initial exciton dynamics in QDs with femtosecond timescales. We observe high exciton diffusivity (10 cm s) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (10-1 cm s). QD solids with larger interdot distances exhibit higher initial diffusivity and a delayed transition to the slower regime, while higher QD packing density and heterogeneity accelerate this transition. The fast transport regime occurs only in materials with exciton Bohr radii much larger than the QD sizes, suggesting the transport of delocalized excitons in this regime and a transition to slower transport governed by exciton localization. These findings suggest routes to control the optoelectronic properties of QD solids.
量子点 (QD) 固体是开发一系列光电设备的新兴平台。因此，了解激子动力学对于开发和优化 QD 器件至关重要。在这里，我们使用瞬态吸收显微镜，在飞秒时间尺度上揭示了 QD 中的初始激子动力学。我们观察到在光激发后的最初几百飞秒内，铅硫属化物 QD 中的激子具有很高的扩散率（10 cm s），随后过渡到较慢的状态（10-1 cm s）。具有较大点间距离的 QD 固体表现出更高的初始扩散率和较慢状态的延迟转变，而更高的 QD 堆积密度和异质性会加速这种转变。快速输运状态仅发生在激子玻尔半径远大于 QD 尺寸的材料中，这表明在该状态下传输离域激子，并过渡到由激子局域化控制的较慢输运。这些发现为控制 QD 固体的光电特性提供了途径。
