Using coherent dynamics to quantify spin-coupling within triplet-exciton/polaron complexes in organic diodes

TL;DR

This paper presents a combined theoretical and experimental approach to quantify spin interactions in organic semiconductors, revealing weak polaron-exciton coupling and distinguishing different coupling regimes.

Contribution

It introduces a spectroscopic method to measure spin-coupling in triplet-exciton/polaron complexes, advancing understanding of their magnetic properties.

Findings

Polaron:exciton exchange is less than 170 MHz, much weaker than intra-exciton coupling.

Triplet-exciton:polaron pairs are identified in organic diodes.

The method distinguishes between different spin-coupling regimes.

Abstract

Quantifying the spin-spin interactions which influence electronic transitions in organic semiconductors is crucial for understanding their magneto-optoelectronic properties. By combining a theoretical model for three spin interactions in the coherent regime with pulsed electrically detected magnetic resonance experiments on MEH-PPV diodes, we quantify the spin-coupling within complexes comprising three spin-half particles. We determine that these particles form triplet-exciton:polaron pairs, where the polaron:exciton exchange is over 5 orders of magnitude weaker (less than 170 MHz) than that within the exciton. This approach providing a direct spectroscopic approach for distinguishing between coupling regimens, such as strongly bound trions, which have been proposed to occur in organic devices.