Melianas Armantas, Kemerink Martijn
Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden.
Adv Mater. 2019 May;31(22):e1806004. doi: 10.1002/adma.201806004. Epub 2019 Feb 4.
The performance of organic optoelectronic devices, such as organic photovoltaic (OPV) cells, is to a large extent dictated by their ability to transport the photogenerated charge, with relevant processes spanning a wide temporal (fs-µs) and spatial (1-100 nm) range. However, time-resolved techniques can access only a limited temporal window, and often contradict steady-state measurements. Here, commonly employed steady-state and time-resolved techniques are unified over an exceptionally wide temporal range (fs-µs) in a consistent physical picture. Experimental evidence confirmed by numerical simulations shows that, although various techniques probe different time scales, they are mutually consistent as they probe the same physical mechanisms governing charge motion in disordered media-carrier hopping and thermalization in a disorder-broadened density of states (DOS). The generality of this framework is highlighted by time-resolved experimental data obtained on polymer:fullerene, polymer:polymer, and small-molecule blends with varying morphology, including recent experiments revealing that low donor content OPV devices operate by long-range hole tunneling between non-nearest-neighbor molecules. The importance of nonequilibrium processes in organic electronic materials is reviewed, with a particular focus on experimental data and understanding charge transport physics in terms of material DOS.
诸如有机光伏（OPV）电池等有机光电器件的性能在很大程度上取决于其传输光生电荷的能力，相关过程跨越很宽的时间范围（飞秒至微秒）和空间范围（1至100纳米）。然而，时间分辨技术只能获取有限的时间窗口，并且常常与稳态测量结果相矛盾。在此，常用的稳态和时间分辨技术在一个异常宽广的时间范围（飞秒至微秒）内，以一致的物理图景实现了统一。经数值模拟证实的实验证据表明，尽管各种技术探测的时间尺度不同，但它们相互一致，因为它们探测的是控制无序介质中电荷运动的相同物理机制——在无序展宽的态密度（DOS）中的载流子跳跃和热化。通过对具有不同形态的聚合物：富勒烯、聚合物：聚合物和小分子共混物获得的时间分辨实验数据突出了该框架的通用性，包括最近的实验揭示低施主含量的OPV器件通过非最近邻分子之间的长程空穴隧穿运行。本文综述了有机电子材料中非平衡过程的重要性，特别关注实验数据以及从材料态密度角度理解电荷输运物理。
