Exciton Quenching at Grain Boundaries in C₆₀ Thin Films

Exciton lifetimes play a critical role in the performance of organic optoelectronic devices. In this work, we investigate how the presence of multiple rotational domains and therefore grain boundaries impacts exciton dynamics in thin films of C₆₀/Au(111) using time- and angle-resolved photoemission spectroscopy (TR-ARPES). We find that films with multiple rotational domains exhibit shorter exciton lifetimes and higher susceptibility to exciton-exciton annihilation, even when one domain dominates. Scanning tunneling microscopy (STM) measurements reveal electronic structure changes resulting from a locally reduced dielectric constant at grain boundaries, suggesting a mechanism for lifetime reduction through exciton funneling and other additional decay channels. These findings highlight the critical role of film quality in determining intrinsic exciton lifetimes and show that minuscule amounts of disorder that are nearly undetectable by ensemble measurements can significantly impact dynamics. These results imply that precise structural control is essential for optimizing the performance of organic optoelectronic devices.