PhD thesis
Simulation-assisted experimental study of excitonic processes in OLEDs:
dissociation and quenching
Abstract
Organic light-emitting diodes (OLEDs) are widely used in modern display technologies due to their high efficiency, flexibility, and compatibility with low-temperature fabrication processes. However, their performance is often limited by exciton loss processes that reduce device efficiency, particularly at high brightness. Understanding and quantifying these processes is therefore essential for the development of OLEDs with improved performance. This thesis presents a simulation-assisted experimental study of excitonic processes in OLEDs, focusing on exciton dissociation and triplet-polaron quenching.
The research combines optical and electrical experiments with three-dimensional kinetic Monte Carlo (3D-KMC) simulations and quantum-chemical calculations. This integrated approach enables an interpretation of experimental observations at the molecular and device levels and provides quantitative insight into exciton dynamics and energy levels in OLED materials.
The first part of the thesis (Chapter 3 and 4) discusses field-induced dissociation (FID) of excitons in OLED materials. By combining field-dependent photoluminescence measurements with 3D-KMC simulations, exciton binding energies are determined for phosphorescent and thermally activated delayed fluorescent (TADF) emitters. Exciton binding energies in the range of 1.0 − 1.3 eV are obtained for the studied OLED materials, dependent on the specific TADF material.
The second part of the thesis (Chapter 5 and 6) focuses on triplet-polaron quenching (TPQ), an important loss mechanism in phosphorescent OLEDs. Through a combination of device experiments and simulations, the mechanisms and rates of TPQ are analyzed for different emitter and host systems. The results provide insight into the role of charge transport, trap states, and material combinations in determining quenching behavior.
Overall, the results demonstrate that simulation-assisted experiments provide a powerful framework for quantitatively understanding excitonic processes in OLEDs. The insights obtained contribute to improved modeling approaches and provide guidance for the design of OLED devices with reduced efficiency roll-off and enhanced performance.