Transient localization of charge carriers in organic semiconductors

在这个合作研究项目中，我们希望阐明有机半导体中的电荷输运机制及其内在局限性。重点将放在最近提出的动态分子无序控制光学性质和载流子输运的建议上，并对注入或激发的载流子的直流迁移率和低频光吸收进行非常具体的预测。分子无序的动力学性质阻碍了载体的长时间定位；即，无序势的涨落破坏了导致安德森局域化的量子干涉。我们的团队由三个知名团队组成，涵盖了从材料纯化和晶体生长、样品表征、器件制造、光谱学、载流子动力学研究、建模和理论描述等各个方面。预计的实验将在高质量的分子单晶上进行，这些单晶显示出优选的空穴（rubrene， pentacene等）或电子传导（二氯萘二胺等），并且可以通过场效应或光激发来掺杂电荷载流子。我们计划测量光学电导率，场效应管迁移率以及噪声谱密度作为晶体方向，温度，频率，载流子密度和掺杂诱导的静态无序的函数。该实验将为分子半导体电子输运中瞬态局域化的发生提供定量证据，从而使我们能够改进和推进这类材料中动态载流子运动的理论概念和建模。

In this collaborative research project we want to elucidate the charge-transport mechanisms in organic semiconductors and their intrinsic limitations. The focus will be on the recent suggestion that dynamical molecular disorder governs the optical properties and charge-carrier transport, with very specific predictions on the dc mobility and low-frequency optical absorption of the charge carriers injected or excited across the energy gap. The dynamical nature of molecular disorder prevents localization of the carriers at long times; i.e. fluctuations of the disorder potential destroy the quantum interferences responsible for Anderson localization.Our team of three high-profile groups completely covers the full range from material purification and crystal growth, sample characterization, device fabrication, optical spectroscopy, investigations of the charge-carrier dynamics, modelling and theoretical description. The projected experiments will be performed on high-quality molecular single crystals showing preferred hole (rubrene, pentacene, etc.) or electron conduction (dichloro-naphthalene-diimde, etc.) and which can be charge carrier-doped by either field-effect or photo-excitations. We plan to measure the optical conductivity, the FET mobility as well as the noise spectral density as a function of crystallographic direction, temperature, frequency, carrier density and doping-induced, static disorder. The experiments will provide quantitative evidence for the occurrence of transient localization in the electronic transport of molecular semiconductors and thus will allow us to improve and advance theoretical concepts and modelling of the dynamical charge carrier motion in this material class.