分子与半导体界面的电荷分离动力学理论研究

To understand all details of charge separation kinetics at an interface formed by molecules placed at a semiconductor surface is of particular interest for photovoltaic devices. The photoinduced exciton formation and the subsequent charge and energy transfer are essential for free carrier formation. The focus of the studies shall be on a typical hybrid system formed by a single molecule or a molecular aggregate attached to semiconductor nanostructures. photoinduced exciton formation, separation into an electron-hole pair across the interface and finally the motion of uncorrelated carriers will be investigated. Based on the specificity of the photoinduced excitation different schemes of electronic level alignment will be studied. The type of photoinduced excitation will be varied. Dissipative processes due to electron - vibrational coupling are accounted for. Plasmon effects of metal nano-particles placed close to the interface are considered, too. Moreover, the prospective work shall elucidate exciton separation at the interface, a possible formation of hybridized quantum states, the change of energy levels related to the oxidized or reduced molecular states, the description of Coulomb-correlated electron-hole pairs, the treatment of nonlinear exciton kinetics and so on. The development of this project will be helpful for illustrating the physical mechanisms of energy and charge transfer at the molecule-semiconductor interface also with a particular impact on the development not only on photovoltaic devices but also on light-harvesting materials and related applications.

分子和半导体界面中的电荷分离过程是决定分子光伏器件光电性质的中心问题，其中光激发作用下激子态的形成及相应的电荷转移和能量转移过程对自由载流子的形成至关重要。项目针对分子或分子聚集体与半导体组成的异质结，通过调节光激发频率与半导体或分子能级之间的关系在界面的不同位置产生激子，研究在界面处分离成电子-空穴对的过程及随后的非相干载流子的运动过程。对影响其动力学过程的因素，如分子和半导体间的能级匹配，外场的激发种类，分子振动引起的耗散过程，金属纳米粒子的表面等离激元效应等进行了考虑和设计。项目关注界面中激子分离所涉及的科学问题如杂化量子态的形成，分子氧化态或还原态引起的能级变化，库仑相关电子-空穴对的描述，非线性激子态的处理等，从而揭示不同能级匹配场景中的分子和半导体界面中的能量转移和电荷转移规律，为合成新型光捕获材料提高光伏器件的效率提供理论基础和指导。

分子聚集体中的多激子效应、激子-激子湮灭效应，分子系统与金属纳米粒子、金属纳米腔或皮米腔中等离激元的相互作用是有机光伏电池和光化学反应等过程的核心问题.对分子体系中的激子及其相关的能量转移、电荷转移以及其与半导体、金属纳米粒子的相互作用的量子层面的研究是本项目的研究重点。 本项目应用原创的算符算术平均场近似方法对分子体系的多激子动力学过程和激子-激子相干过程以及相关的能量转移进行微观理论描述，得到分子激子动力学过程的规律性认识。同时我们结合宏观量子电动力学理论和开放量子系统理论，提出了半经典理论讨论等离激元皮米腔中单个分子的荧光特性，得到了与相关实验一致的结果，深入理解了分子发射体在金属纳米腔和皮米腔中的相互作用。电子损失能谱作为一种近场探测方法，可以更加有效地用于分子体系与等离激元的强耦合的研究，我们研究了不同纳米棒和分子介电层强耦合导致的电子损失能谱的拉比劈裂，探讨了近场方法激发暗模式的独特优势，深入研究了表面等离激元导致的近场对分子层元激发信号的增强作用，得到了规律性的认识，为提高光伏器件的能量转换效率提供理论基础和设计指导。