Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 13-3057, Cambridge, Massachusetts 02139, USA.
Queens College and Graduate Center, Department of Physics, The City University of New York, 6530 Kissena Boulevard, Flushing, New York 11367, USA.
Nat Commun. 2014 Apr 16;5:3646. doi: 10.1038/ncomms4646.
Transport of nanoscale energy in the form of excitons is at the core of photosynthesis and the operation of a wide range of nanostructured optoelectronic devices such as solar cells, light-emitting diodes and excitonic transistors. Of particular importance is the relationship between exciton transport and nanoscale disorder, the defining characteristic of molecular and nanostructured materials. Here we report a spatial, temporal and spectral visualization of exciton transport in molecular crystals and disordered thin films. Using tetracene as an archetype molecular crystal, the imaging reveals that exciton transport occurs by random walk diffusion, with a transition to subdiffusion as excitons become trapped. By controlling the morphology of the thin film, we show that this transition to subdiffusive transport occurs at earlier times as disorder is increased. Our findings demonstrate that the mechanism of exciton transport depends strongly on the nanoscale morphology, which has wide implications for the design of excitonic materials and devices.
纳米尺度激子能量的输运是光合作用的核心，也是各种纳米结构光电设备（如太阳能电池、发光二极管和激子晶体管）运行的核心。特别重要的是激子输运与纳米尺度无序之间的关系，这是分子和纳米结构材料的固有特性。在这里，我们报告了分子晶体和无序薄膜中激子输运的空间、时间和光谱可视化。我们使用并五苯作为典型的分子晶体，成像结果表明激子输运是通过随机漫步扩散进行的，随着激子被捕获，激子输运会转变为亚扩散。通过控制薄膜的形态，我们表明随着无序度的增加，这种向亚扩散输运的转变会更早发生。我们的发现表明，激子输运的机制强烈依赖于纳米尺度形态，这对激子材料和器件的设计具有广泛的影响。
