Role of Electron--Electron Interactions on Spin Effects in Electron--Hole Recombination in Organic Light Emitting Diodes

Details Role of Electron--Electron Interactions on Spin Effects in Electron--Hole Recombination in Organic Light Emitting Diodes Role of Electron--Electron Interactions on Spin Effects in Electron--Hole Recombination in Organic Light Emitting Diodes

2004-11-18

arxiv.org/abs/cond-mat/0411466v1

Physics

Condensed Matter

Strongly Correlated Electrons

29 pages, 10 figures. To appear in 'Organic Light Emitting Diodes' Ed. J. Shinar, JohnWiley

Scientific paper

We extend our theory of electron--hole recombination in organic light emitting diodes to investigate the possibility that high energy singlet and triplet excited states with large electron--hole separations are generated in such processes, over and above the lowest singlet and triplet excitons. Our approach involves a time-dependent calculation of the interchain / intermolecular charge--transfer within model Hamiltonians that explicitly include electron-electron interactions between the $\pi$-electrons. We show that the electron--hole recombination reaction can be viewed as a tunneling process whose cross section depends on both the matrix element of the interchain part of Hamiltonian and the energy difference between the initial polaron--pair state and the final neutral states. There occurs a bifurcation of the electron--hole recombination path in each of the two spin channels that leads to the generation of both the lowest energy exciton and a specific high energy charge-transfer state, with the matrix elements favoring the lowest energy exciton and the energy difference factor favoring the higher energy state. The overall effect of the electron--electron interactions is to enhance the singlet:triplet yield ratio over the value of 0.25 predicted from statistical considerations that are valid only within noninteracting models.

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