Collaborative Research: Quasiparticle Transport in Organic Materials: Vibrational Dressing, Static Disorder, Nanoscale Confinement, and Quantum Effects

Missouri University Of Science And Technology, Rolla MO

Investigators

Abstract

0097210 Parris This is a Collaborative Research Project between the University of New Mexico and the University of Missouri at Rolla. The research performed is theoretical, employ analytic and computer methods, and deals with fundamental issues of quasiparticle transport in organic materials on the one hand, and applications to technologically important systems and devices on the other hand. Among the fundamental issues it addresses are dynamic disorder, static disorder, intense applied fields, carrier-carrier interactions, and quantum effects arising from variation in the characteristic size of the systems under study. Breaking the translational invariance by strong interactions of quasiparticles, such as electrons, with vibrations and other oscillatory motions of molecules, constitutes dynamic disorder. Some of the issues to be addressed are very new, while others are longstanding but unresolved: What is the nature of the fundamental carriers of charge and enegy in organic solids? To what extent are they localized or extended in space, free or associated with distortions around them (polaronic), coherent or incoherent in their motion? What new effects on dynamics may be expected as a result of system size variation from the mesoscale to the nanoscale? Theoretical investigations to be performed will seek to determine conditions under which transport is normal or (and to what quantitative extent) anomalous in the sense of dispersive, so that application of ordinary equilibrium statistical mechanics may not mislead quantitative assessment of experiment. Investigations will also address the possibility of formation, as well as the effects on experiments, of composite particles: electron-photon (e.g., polaron), exciton-phonon (e.g., excimer), phonon-phonon (e.g., vibron), and exciton-photon (e.g., polariton) in limits in which the characteristic motion times of the constituent elements are disparate. Static disorder, both spatial and energetic, arises in organic materials from random molecular packings, chemical impurities, charge-dipole interactions, and orientational and spatial inhomogeneities. Such mechanisms can, and often do, lead to static disorder chacterized by substantial spatial correlations. Research will focus on the sources and possible control of such correlations and their effects on quasiparticle transport. Studies will be performed of the interplay and competition that occurs between correlated and uncorrelated sources of disorder, and a variety of effects, such as rate inversion in polaronic systems, that can arise from a combination of high fields, the polaronic nature of charge, and disorder. On the basis of insights gained through this work on fundamental aspects of quantum transport of quasiparticles, the research will focus on a number of practical device issues and phenomena including the screening of charge-dipole interactions, the mutual interaction of charges during injection, interfacial effects in organic light-emitting diodes and field effect transistors, recombination, and photogeneration. It will also address special device features such as geometrical constraints, reduced dimensionality, reduced phase space, and particularly the nanoscale (more appropriately the meso-micro-nano-scale) transition. %%% This is a Collaborative Research Project between the University of New Mexico and the University of Missouri at Rolla. The research performed is theoretical, employ analytic and computer methods, and deals with fundamental issues of quasiparticle transport in organic materials on the one hand, and applications to technologically important systems and devices on the other hand. ***