Exciton-exciton annihilation in organic polariton microcavities

We investigate the incoherent diffusion of excitons in thin films (5.1±0.1nm thick) of a highly absorbing J-aggregated cyanine dye material (106 cm^-1 absorption constant) as the excitonic component of a polariton microcavity. Under high-intensity pulsed laser excitation, the J-aggregated molecular films exhibit significant exciton-exciton annihilation, indicating a large exciton diffusion radius of more than 100 nm. When the material is strongly coupled to a cavity, the polaritonic structure also shows exciton-exciton annihilation, which is a competing process against the establishment of a threshold population of polaritons needed for polariton lasing. This study suggests that exciton-exciton annihilation is a loss process which can significantly increase the lasing threshold in polariton microcavities.