期刊
ACS Nano
卷 10, 期 7, 页码 7208-7215出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.6b03700
关键词
energy transfer; femtosecond transient absorption spectroscopy; pump-probe microscopy; exciton diffusion; quantum dot solids
类别
资金
- National Science Foundation [NSF-CHE-1555005]
- Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-FC02-04ER15533]
- Materials Science of Actinides, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science [DE-SC0001089]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1555005] Funding Source: National Science Foundation
Long-range charge and exciton transport in quantum dot (QD) solids is a crucial challenge in utilizing QDs for optoelectronic applications. Here, we present a direct visualization of exciton diffusion in highly ordered CdSe QDs superlattices by mapping exciton population using ultrafast transient absorption microscopy. A temporal resolution of similar to 200 fs and a spatial precision of similar to 50 nm of this technique provide a direct assessment of the upper limit for exciton transport in QD solids. An exciton diffusion length of similar to 125 nm has been visualized in the 3 ns experimental time window and an exciton diffusion coefficient of (2.5 +/- 0.2) x 10(-2) cm(2) s(-1) has been measured for superlattices constructed from 3.6 nm CdSe QDs with center-to-center distance of 6.7 nm. The measured exciton diffusion constant is in good agreement with FOrster resonance energy transfer theory. We have found that exciton diffusion is greatly enhanced in the superlattices over the disordered films with an order of magnitude higher diffusion coefficient, pointing toward the role of disorder in limiting transport. This study provides important understandings on energy transport mechanisms in both the spatial and temporal domains in QD solids.
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