Abstract
Organic nanofibers have found various applications in optoelectronic devices. In such devices, exciton diffusion is a major aspect concerning their efficiency. In the case of singlet excitons, Förster transfer is the mechanism responsible for this process. Temperature and morphology are factors known to influence exciton diffusion but are not explicitly considered in the expressions for the Förster rate. In this work, we employ a Kinetic Monte Carlo (KMC) model to investigate singlet exciton diffusion in para-hexaphenyl (P6P) and α-sexithiophene (6T) nanofibers. Building from previous experimental and theoretical studies that managed to obtain temperature dependent values for Förster radii, exciton average lifetimes and intermolecular distances, our model is able to indicate how these parameters translate into diffusion coefficients and diffusion lengths. Our results indicate that these features strongly depend on the coordination number in the material. Furthermore, we show how all these features influence the emitted light color in systems composed of alternating layers of P6P and 6T. Finally, we present evidence that the distribution of exciton displacements may result in overestimation of diffusion lengths in experimental setups.
Highlights
Among the materials employed in optoelectronic applications, organic nanofibers have received considerable attention thanks to their capacity to self-assemble and the tunability of their optical properties[8,9,10]
We argue that the distribution of exciton displacements may lead to overestimation in exciton diffusion lengths under experimental conditions
Our results show that exciton diffusion coefficients and diffusion lengths may be considerably affected by the coordination number found in the morphology of the system, if a change in this number corresponds to an increase in the average intermolecular distance
Summary
Among the materials employed in optoelectronic applications, organic nanofibers have received considerable attention thanks to their capacity to self-assemble and the tunability of their optical properties[8,9,10]. The mechanism responsible for singlet exciton diffusion is the Förster resonance energy transfer[14,15,16] This is a non-radiative transition that requires the existence of an overlap between the emission and absorption spectra of the donor and acceptor molecules, respectively. To take into account these more complex issues, Kinetic Monte Carlo (KMC) models are often employed in the study of exciton diffusion[7,18,23,24,25,26] These models must be able to calculate Förster rates and probabilities to decide the behavior of each exciton at every step of the simulation. In the two dimensional case, the distances between a site and all its neighbors are not equal This affects the transfer rates, the recombination probability and the diffusion length. Analytical models are impractical when studying systems composed by more than one material, since the Förster radii are different, resulting in an asymmetry between the possibility of Förster transfers from one material to the other
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