Theory and models for electronic dynamics in organic type II semiconductors

休斯顿大学的Eric Bittner获得了化学系化学理论、模型和计算方法计划以及材料研究部凝聚态物质和材料理论计划的支持，以在太阳能转换的感兴趣的光激发材料中进行电荷和能量传输方面的研究。这项工作的目标是了解电子、核和光在有机聚合物中相互作用的行为，特别是那些聚合物的重复部分具有小缺陷或强烈无序或与其他材料接触的聚合物。这项工作是为了洞察和推进能源应用和设备的材料设计，例如利用阳光发电的塑料设备。虽然这些系统中的量子力学过程发生在超短(10^-15 S)时间尺度上，但它们直接影响出现在较长时间尺度(介观尺度)上的器件行为。然而，到目前为止，由于缺乏对这些中尺度过程的详细了解和控制，研究人员无法充分利用这些影响。为此，这项研究试图了解更长时间和更长时间尺度上的相互作用是如何产生紧急现象的。Bittner小组在这一领域的工作是发展先进的理论方法来研究由光子吸收引发的电荷和能量转移过程。共轭大分子的电学和光学性质是由于有机半导体中含有强电子关联和电子与分子结构耦合的离域电子体系。这个项目探索了量子相干和量子纠缠如何影响光激发后的初始电荷分离，并有助于抑制随后形成的电荷复合。理论方法结合使用晶格模型描述聚合物/富勒烯体相异质结界面的介观结构--用从头算和实验数据进行参数化--和描述声子驱动的非绝热态间电子跃迁的无时间卷积主方程方法。这一方法是以一系列模型供体-桥-受体分子为基准的，这些分子最初是由克洛斯和米勒在他们的经典工作中研究的，证实了马库斯倒置制度。其他组成部分包括开发有机聚集体中激子/声子极化子的理论模型。J-聚集体中的极化玻色凝聚的工作仍在继续，特别是考虑到麻省理工学院布拉维奇小组最近的实验。这项工作的另一个方面是在受限几何中的激子的光物理中，人们可以利用珀塞尔效应来制备实验探测器无法获得的状态。

Eric Bittner from the University of Houston is supported in an award by the Chemical Theory, Models and Computational Methods program in the Division of Chemistry and by the Condensed Matter and Materials Theory program in the Division of Materials Research to conduct research in charge and energy transport in photo-excited materials of interest for solar energy conversion. The goal of this work is to understand the behavior of electrons, nuclei, and light interacting in organic polymers, particularly those where the repeating parts of the polymers have small defects or are strongly disordered or come into contact with other materials. This work is to gain insight and advance materials design in energy applications and devices, e.g., plastic devices that generate electricity from sunlight. While quantum mechanical processes in these systems occur on an ultra short (10^-15 s) time scale, they directly influence device behavior emerging on longer time scales (mesoscales). However, lack of detailed understanding and control of these mesoscale processes has thus far prevented researchers from fully exploiting these effects. To this end, this research seeks understanding of how emergent phenomena arise due to interactions beyond on longer time and length scales.The Bittner group's work in this field is the development of advanced theoretical methods for studying charge and energy transfer processes initiated by the absorption of photons. The electronic and optical properties of conjugated macromolecules are due to the delocalized pi-electron systems involving strong electron correlations and coupling of electrons to molecular structure in oorganic semiconductors. This project explores how quantum coherence and quantum entanglement both impact the initial charge separation following photoexcitation and help to suppress subsequent recombination of charges once they have formed. The theoretical approach combines the use of lattice models to describe the mesoscale structure of polymer/fullerene bulk heterojunction interafaces -- parameterized using ab initio and experimental data -- and time-convolutionless master equation methods to describe non-adiabatic interstate electronic transition as driven by phonons. This approach is being benchmarked against a series of model donor-bridge-acceptor molecules originally studied by Closs and Miller in their classic work that confirmed the Marcus inverted regime. Other components include developing theoretical models for excitons/phonon polaritons in organic aggregates. Work is continuing in polariton Bose Condensation in J-aggregatea, especially in light of recent experiments by Bulovic's group at MIT. An additional aspect of the work is in the photophysics of excitons in confined geometries, where one can exploit the Purcell effect to prepare states that are otherwise inaccessible to experimental probes.