Spin-dependent polaron recombination in conjugated polymers

Abstract

We simulate the interchain polaron recombination process in conjugated polymer systems using a nonadiabatic molecular dynamics method, which allows for the coupled evolution of the nuclear degrees of freedom and multiconfigurational electronic wavefunctions. Within the method, the appropriate spin symmetry of the electronic wavefunction is taken into account, thus allowing us to distinguish between singlet and triplet excited states. It is found that the incident polarons can form an exciton, form a bound interchain polaron pair, or pass each other, depending on the interchain interaction strength and the strength of an external electric field. Most importantly, we found that the formation of singlet excitons is considerably easier than triplet excitons. This shows that in real organic light emitting devices, the electroluminescence quantum efficiency can exceed the statistical limitation value of 25%, in agreement with experiments.

Dynamics of exciton transfer in coupled polymer chains

“…The model Hamiltonian we have adopted is the Su-Schrieffer-Heeger+Pariser-Parr-Pople (SSH+PPP) model 15,18,19 with a Brazoskii-Kirova-type symmetrybreaking term. 20,21 This Hamiltonian can be written as…”

Dynamics of charge separation at an organic donor-acceptor interface

“…The system can, however, be considered as a model system which is able to grasp the essentials of most (nondegenerate) conjugated polymers. We adopt the parameters developed by Miranda et al [19,20], which also were used in our previous work [18,21,22]. Specific attention is given to three parameters: the interchain hopping t v and t DA , the screening of the Coulomb potential β, and the band offset E. Three sets of simulations are presented below; in each such simulation we vary one of these parameters and keep the other two at a fixed value.…”

“…The evolution of the system is obtained by time integration of the two sets of equations of motion. The numerical methods have been described previously [18,21].…”

Concentration effects on intrachain polaron recombination in conjugated polymers

“…Recently, Sun and Stafstro ¨m used the Su-Schrieffer-Heeger (SSH) model to simulate the recombination process between an oppositely charged polaron pair in two coupled conjugated polymer chains. 13 Their results show that the spin-dependent recombination mechanism can form an exciton or a bound interchain polaron pair depending on the interchain coupling and the external electric field strength. An et al 14 and Li et al 15 have also investigated the polaron recombination mechanism in the scope of a tight-binging approach.…”