Ultrafast long-range energy transport via light-matter coupling in organic semiconductors*

Efficient energy transport over macroscopic length scales is highly desirable in organic semiconductors. Here, we show this can be achieved at room temperature in a range of chemically diverse, organic semiconductor thin films through strong light-matter coupling to form exciton-polaritons, despite the absence of an external cavity. We directly visualize energy transport via femtosecond transient absorption microscopy with sub-10 fs temporal and sub-10 nm spatial precision and find energy transport lengths of up to 270 nm at effective velocities of up to 5 x 10⁶ m s^-1. We find additional evidence of strong light-matter coupling via peak splittings in the reflectivity spectra and emission from collective polariton states. These results and the design rules that follow will enable a new generation of organic optoelectronic and light harvesting devices based on robust cavity-free exciton-polaritons.