Quenching of excitons at grain boundaries in C60 thin films

TL;DR

This study reveals that grain boundaries in C60 thin films significantly shorten exciton lifetimes due to local dielectric changes, emphasizing the importance of structural control for device performance.

Contribution

It demonstrates how grain boundaries and disorder in C60 films affect exciton dynamics, providing insights into the role of film quality in optoelectronic efficiency.

Findings

Shorter exciton lifetimes at grain boundaries

Evidence of exciton-exciton annihilation in disordered films

Local dielectric constant reduction at grain boundaries

Abstract

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 evidence of exciton-exciton annihilation, even when one domain predominates. Scanning tunneling microscopy (STM) measurements reveal electronic structure changes resulting from a locally reduced dielectric constant at grain boundaries, providing 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 optimize the performance of organic optoelectronic devices.