CAREER: Solid State Solvation in Doped & Nanostructured Organic Thin Films: A Novel Method for Tailoring Energy Level Structure of Organic Materials in Active Optoelect. Devic

Vladimir Bulovic教授最近展示了一种新的通用方法，通过分子间偶极子-偶极子相互作用来调节有机膜内局部电场的强度，从而调节有机材料的能级结构。他的团队现在将应用这种“固态溶剂化”（SSS）效应来演示实用、高效的有机光电器件，如有机led、激光器和太阳能电池，并对这一现象进行理论理解。SSS效应存在于每一种有机固体分子中，但在强极性材料和复合材料中最明显。它起源于相邻分子之间的偶极子-偶极子相互作用，产生强大的局部电场，拉伸分子内键的长度并使分子上的电荷分布变形。这种分子结构的物理变化表现在分子的能级结构的改变上，我们可以利用它来优化有机光电器件的性能。Bulovic先前证明，在固体薄膜中极性有机分子之间的偶极子-偶极子相互作用中产生的局部电场可以导致分子能级的移动超过0.25 eV，调整相同分子物种的发光从黄色到橙色再到红色。在这个项目中，他的团队将扩展最初的研究，并利用偶极子-偶极子相互作用来调整有机异质结界面的载流子注入特性，修改混合有机层中从宿主到掺杂的激子能量转移率，并在高效磷光有机材料中获得三重态能级。这些效应将被优化，以提高有机发光二极管的发光效率，降低有机激光器的激光阈值，提高有机太阳能电池的发光效率。定量分子有机薄膜中分子间相互作用的理论框架目前尚不清楚，将在本计划内发展。在这个项目中发现的发现本质上是基础性的，并将对分子有机固体在光电器件中的实际应用产生强烈的影响。他们将增强对分子有机材料广阔领域的理解和适用性，影响有机薄膜、异质结、多层、量子阱和纳米有机材料的处理。这些发现将被纳入研究生“有机光电子学研讨会”中，Vulovic教授目前正在为麻省理工学院的研究生课程做准备。

Professor Vladimir Bulovic recently demonstrated a new general method for tuning theenergy level structure of organic materials by adjusting the strength of the local electricfield inside the organic films with intermolecular dipole-dipole interactions. His groupwill now apply this "solid state solvation" (SSS) effect to demonstrate practical, efficientorganic optoelectonic devices such as organic LEDs, lasers, and solar cells, and develop atheoretical understanding of this phenomenon. The SSS effect is present in everymolecular organic solid, but is most clearly observed in strongly polar materials andcomposites. It originates from dipole-dipole interactions between neighboring moleculesthat generate strong local electric fields, stretching the intramolecular bond lengths anddeforming charge distributions on molecules. This physical change in the molecularstructure is manifested in the modified energy level structure for the molecule, which wecan utilize to optimize performance of organic optoelectronic devices.Prof. Bulovic previously demonstrated that local electric fields generated in dipole-dipoleinteractions between polar organic molecules in a solid thin film can result in a shift ofmolecular energy levels by more than 0.25 eV, tuning the luminescence of the samemolecular species from yellow to orange to red. In this program his group will extend theinitial studies and utilize dipole-dipole interactions to tune the carrier injection propertiesat organic heterojunction interfaces, modify exciton energy transfer rates from the host tothe dopant in mixed organic layers, and access triplet energy levels in efficientphosphorescent organic materials. These effects will be optimized to improveluminescence efficiencies of organic LEDs, lower lasing thresholds of organic lasers, andincrease photogeneration efficiency of organic solar cells. The theoretical frameworkquantifying intermolecular interactions in molecular organic thin films is not presentlyknown and will be developed within this program.Findings discovered in the course of this program are fundamental in nature and will havea strong impact on practical applications of molecular organic solids in optoelectronicdevices. They will enhance the understanding and the applicability of the vast field ofmolecular organic materials, influencing treatment of organic thin films, heterojunctions,multilayers, quantum wells, and nano-patterned organic materials. These findings will beincorporated in the graduate "Seminar on Organic Optoelectronics" that Prof. Vulovic ispresently preparing for the MIT graduate curriculum.