Photon-Assisted Oxygen Diffusion and Oxygen-Related Traps in Organic Semiconductors

摘要

Organic molecular crystals represent an excellent platform for fundamental studies of optoelectronic properties of organic semiconductors. Rubrene, in particular, has attracted significant attention due to a very low density of charge traps, record-high charge carrier mobility, and a very large micrometer-scale exciton diffusion length. In this study, using rubrene as a model compound questions related to the interaction of crystalline organic semiconductors with oxygen are addressed. Although the chemistry of photo-oxidation of rubrene in solution and gas phases is understood based on self-sensitized photo-oxidation (see for example, Ref.), the mechanism of oxygen incorporation and its effect on the photophysical properties of crystalline rubrene still remain controversial. Mitrofanov et al. identified an oxygen-related in-gap band in photo-oxidized rubrene by means of a two-photon photoluminescence excitation spectroscopy and showed that oxygen is concentrated near the surface of the crystals. Krellner et al. revealed that an oxygen-related impurity forms an acceptor-like in-gap state in rubrene with an energy ≈0.28 eV above the highest occupied molecular orbital (HOMO). X. Song et al.