Quantum molecular dynamics study of polaron recombination in conjugated polymers

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Abstract
We examine the dynamics of polaron recombination in conjugated polymer systems using mixed quantum classical molecular dynamics. The model treats the particle-hole pair as a fully correlated two-particle quantum mechanical wave function interacting with a one-dimensional classical vibrational lattice. This description allows a natural evolution of the particle-hole wave function from the polaron limit to the exciton limit, and we have performed real-time simulations of the coupled nuclear and electronic dynamics associated with the scattering of polarons into exciton states. We use these simulations to calculate cross sections for exciton formation as a function of spin state, and explore the variation of these cross sections with respect to changes in the magnitude of the particle-hole Coulomb interaction and the effective masses of the quasiparticles. Our results indicate that for an optimal choice of parameters the electroluminescence quantum yield may be as high as 59%, substantially greater than the 25% predicted by simple spin statistics. We interpret these results in a diabatic framework, and suggest strategies for the design of organic systems for use in electroluminescent devices.