Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays

Exciton transport in most organic materials is based on an incoherent hopping process between neighboring molecules. This process is very slow, setting a limit to the performance of organic optoelectronic devices. In this Article, we overcome the incoherent exciton transport by strongly coupling localized singlet excitations in a tetracene crystal to confined light modes in an array of plasmonic nanoparticles. We image the transport of the resulting exciton-polaritons in Fourier space at various distances from the excitation to directly probe their propagation length as a function of the exciton to photon fraction. Exciton-polaritons with an exciton fraction of 50% show a propagation length of 4.4 mu m, which is an increase by 2 orders of magnitude compared to the singlet exciton diffusion length. This remarkable increase has been qualitatively confirmed with both finite-difference time-domain simulations and atomistic multiscale molecular dynamics simulations. Furthermore, we observe that the propagation length is modified when the dipole moment of the exciton transition is either parallel or perpendicular to the cavity field, which opens a new avenue for controlling the anisotropy of the exciton flow in organic crystals. The enhanced exciton-polariton transport reported here may contribute to the development of organic devices with lower recombination losses and improved performance.

Automated summary

In this study, the limitations of incoherent exciton transport in organic materials were overcome by strongly coupling localized singlet excitations with confined light modes. The resulting exciton-polaritons exhibited significantly longer propagation lengths compared to singlet exciton diffusion. The anisotropy of exciton flow in organic crystals was also found to be modulated by the dipole moment of the exciton transition. These findings are important for the development of high-performance organic devices with lower recombination losses.