arXiv subjects

Reinder Coehoorn

Publications and source records attributed to Reinder Coehoorn.

3 recordsLinked to original sources

arXiv2025

Dipole-quadrupole coupling in triplet exciton-polaron quenching in a phosphorescent OLED emission layer

Improving the efficiency and stability of organic light-emitting diodes (OLEDs) will further expand their present success in display applications. Triplet exciton-polaron quenching (TPQ) is an important cause of limited efficiency and stability in modern phosphorescent OLEDs, where triplet excitons are the emitting species. Lack of understanding of the TPQ mechanism in these OLEDs impedes the development of more efficient and stable OLEDs. We investigate the TPQ mechanism for triplet excitons on a phosphorescent guest interacting with hole polarons on a host. Our quantum-chemical calculations show that at distances relevant for TPQ the Förster approximation for the TPQ rate fails and that dipole-quadrupole coupling is dominant. This resolves a discrepancy between estimates of the TPQ rate obtained from an OLED device study and from the overlap between the emission spectrum of the emitter and absorption spectrum of the charged host. Equivalently to the Förster radius for dipole-dipole TPQ, the dipole-quadrupole TPQ rate can be quantified by a dipole-quadrupole radius obtained from the overlap between the emission spectrum of the emitter and the quadrupolar absorption spectrum of the charged host. The findings of this work are expected to have a broad relevance and to be useful in developing phosphorescent emitter-host combinations with reduced TPQ.

physics.atm-clus↗

arXiv2019

Quantitative Predictions of Photoelectron Spectra in Amorphous Molecular Solids from Multiscale Quasiparticle Embedding

We present a first-principles-based multiscale simulation framework for quantitative predictions of the high-energy part of the Ultraviolet Photoelectron Spectroscopy (UPS) spectra of amorphous molecular solids. The approach combines a deposition simulation, many-body Green's Function Theory, polarizable film-embedding, and multimode electron-vibrational coupling and provides a molecular-level view on the interactions and processes giving rise to spectral features. This insight helps bridging the current gap between experimental UPS and theoretical models as accurate analyses are hampered by the energetic disorder, surface-sensitivity of the measurement and the complexity of excitation processes. In particular this is relevant for the unambiguous determination the highest occupied molecular orbital energy (HOMO) of organic semiconductors, a key quantity for tailoring and engineering new opto-electronic devices. We demonstrate the capabilities of the simulation approach studying the spectrum of two isomers of 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as archetypical materials showing a clearly separated HOMO peak in experiment. The agreement with experiment is excellent, suggesting that our approach provides a route for determining the HOMO energy with an accuracy better than 0.1eV.

cond-mat.mtrl-sci↗

arXiv2009

First-principles study of the dipole layer formation at metal-organic interfaces

We study the dipole layer formed at metal-organic interfaces by means of first-principles calculations. Interface dipoles are monitored by calculating the work function change of Au, Ag, Al, Mg and Ca surfaces upon adsorption of a monolayer of PTCDA (3,4,9,10-perylene-tetra-carboxylic-di-anhydride), perylene or benzene molecules. Adsorption of PTCDA leads to pinning of the work function for a range of metal substrates. It gives interface dipoles that compensate for the difference in the clean metal work functions, leading to a nearly constant work function. In contrast, adsorption of benzene always results in a decrease of the work function, which is relatively constant for all metal substrates. Both effects are found in perylene, where adsorption on low work function metals gives work function pinning, whereas adsorption on high work function metals gives work function lowering. The work function changes upon adsorption are analyzed and interpreted in terms of two competing effects. If the molecule and substrate interact weakly, the molecule pushes electrons into the surface, which lowers the work function. If the metal work function is sufficiently low with respect to the unoccupied states of the molecule, electrons are donated into these states, which increases the binding and the work function.

cond-mat.mtrl-sci↗