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

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

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