Ultrafast Exciton Dynamics and Charge Transfer at PTCDA/Metal Interfaces

Abstract

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.

Evidence for Hybrid Inorganic–Organic Transitions at the WS2/Terrylene Interface

“…The bare observation of new peaks in an absorption spectrum is not necessarily an unambiguous proof of the hybrid character of the transition, as differences in growth conditions and changes to the dielectric environment can simply cause optical resonances to (dis-)appear. One way to obtain additional information on the character of a new transition is the use of ultrafast spectroscopy, [26][27][28][29] which probes the changes of the sample properties under nonequilibrium conditions after photoexcitation and allows the educated choice of excitation energy that selectively excites different transitions and/or regions in the sample.…”

Hydrogen-bonded one-dimensional molecular chains on ultrathin insulating films: Quinacridone on KCl/Cu(111)

“…Lowenergy electron diffraction (LEED) and scanning tunneling microscopy (STM) studies have shown that the growth of such 1D molecular chains on metals can be controlled through the substrate temperature and the coverage rate. However, on * eric.le-moal@universite-paris-saclay.fr the one hand, hybridization of the molecular orbitals and the metal surface states due to direct adsorption on the metal strongly alters the excitonic properties of the molecules [35]. On the other hand, the use of insulating substrates prevents the use of surface science tools based on charged particles, such as LEED and STM.…”

Influence of N-introduction on the electronic structure and properties of polyacenes: experiment and quantum chemistry in concert

“…This includes electronattachment and electron-detachment levels of the interfaces (transport levels) as well as optical gaps and exciton binding energies. 21,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] The energies of singlet electronic transitions (e.g. S 0 -S 1 , optical gaps) have been investigated with HREELS, [41][42][43][44][45][46][47][48] Furthermore, HREELS opens up the opportunity to gain insight into the energetic position of triplet states, which are not accessible with conventional (linear) optical methods.…”