Paradoxical Suppression of Exciton Diffusion by Long-Range Interactions: A Large-Scale Nonadiabatic Dynamics Study

Exciton diffusion is crucial for various optoelectronic applications of organic semiconductors, yet the underlying mechanisms remain to be fully elucidated. We here focus on the Frenkel exciton and make a systematic large-scale nonadiabatic dynamics study of exciton diffusion. It is found that long-range interactions could enhance exciton diffusion if the nearest-neighbor exciton coupling is relatively weak compared with the exciton-phonon coupling strength. When the nearest-neighbor coupling becomes strong enough, however, we uncover a paradoxical suppression of exciton diffusion (PSED) by long-range interactions. In general, both the temperature and interaction range could simultaneously change the energy distribution and delocalization strength of the exciton. The competition between these two effects results in the complex dynamics of PSED due to long-range interactions. These findings have deepened our understanding of exciton diffusion, which may facilitate the rational design of organic materials for improving the energy conversion efficiency of solar cells.