Ultralong‐Range Energy Transport in a Disordered Organic Semiconductor at Room Temperature Via Coherent Exciton‐Polariton Propagation

Abstract

Amorphous molecular solids are inherently disordered, exhibiting strong exciton localization. Optical microcavities containing such disordered excitonic materials have been theoretically shown to support both propagating and localized exciton‐polariton modes. Here, the ultrastrong coupling of a Bloch surface wave photon and molecular excitons in a disordered organic thin film at room temperature is demonstrated, where the major fraction of the polaritons are propagating states. The delocalized exciton‐polariton has a group velocity as high as 3 × 107 m s–1 and a lifetime of 500 fs, leading to propagation distances of over 100 µm from the excitation source. The polariton intensity shows a halo‐like pattern that is due to self‐interference of the polariton mode, from which a coherence length of 20 µm is derived and is correlated with phase breaking by polariton scattering. The demonstration of ultralong‐range exciton‐polariton transport at room temperature promises new photonic and optoelectronic applications such as efficient energy transfer in disordered condensed matter systems.Long‐range excitation energy transport over 100 µm is demonstrated in an amorphous organic thin film on a distributed Bragg reflector. The exciton exhibits ultrastrong coupling with a Bloch surface wave photon, overcoming the short exciton diffusion lengths of disordered material systems. The halo‐like polariton propagation pattern is explained by self‐interference.