Ultrafast Exciton Dynamics and Charge Transfer at PTCDA/Metal Interfaces

The functionality of organic electronic devices is governed by the dynamics of charge carriers and excited states in organic semiconductors. In particular, the relaxation of excitons and the transfer of charge carriers at metal electrodes crucially determine the performance of organic optoelectronic devices. In a combined experimental study we apply time-resolved photoluminescence and two-photon photoemission to reveal the ultrafast exciton dynamics and charge transfer at prototype organic/metal contacts comprising thin molecular films on single-crystalline noble-metal surfaces. On the basis of experiments with systematically varied film thicknesses, we relate the strong quenching of Frenkel excitons and charge transfer excitons to the wave function overlap with the metal, indicating charge transfer as the dominant relaxation pathway. Moreover, the presence of an electronic interface state is found to facilitate the transfer of excited carriers across the organic/metal interface.