18th European School on Molecular Nanoscience (ESMolNa2025) 18th-22nd May 2025

Scientific Summary

This study presents a detailed investigation into the degradation mechanisms of organic light-emitting diodes (OLEDs), specifically those employing a phosphorescent Ir(MDQ)2(acac) emitter. The main goal was to simultaneously analyse electronic and excitonic changes in OLEDs under constant current stress, combining intermittent electro-optical characterization with device simulation. Key findings include evidence for the generation of trap states during operation, detected via capacitance-voltage (C-V), capacitance-frequency (C-f), and current-voltage (I-V) measurements. While electroluminescence (EL) showed the expected decrease in luminance, modulated photoluminescence spectroscopy (MPLS) revealed a complex evolution of exciton quenching. Below 2.5 V, degradation suppressed photoluminescence (PL) due to increasing non-radiative recombination, but above 2.5 V, degradation counter-intuitively enhanced PL. These observations highlight a complex interplay between trap characteristics, charge injection, and exciton interactions during OLED degradation.

Why it Matters

Understanding these complex and often counter-intuitive degradation mechanisms is crucial for improving the operational lifetime of OLEDs, especially in high-luminance applications where stability remains a significant challenge. By elucidating the interplay between electronic and excitonic changes, this research provides vital insights that can guide the rational design of materials and device architectures to mitigate degradation and ultimately lead to more durable and efficient OLED technology.

Publication Details

Stanzani, E., Georgakopoulos, V., Zeder, S., Ruhstaller, B., Jenatsch, S. (2025), Excitonic Mechanisms Evolution during OLEDs degradation. Abstract 21-2, 18th European School on Molecular Nanoscience (ESMolNa2025) Book of Abstracts, Santa Pola (Alicante, Spain), May 18-22, 2025..

Fluxim Tools Used

The commercial software Setfos (Fluxim AG) was employed for electro-optical simulations of the OLED device. Setfos was utilized to assess the impact of different degradation processes within the device, which helped in explaining the observed experimental changes in both electronic and excitonic mechanisms. This simulation capability also allowed researchers to propose modifications to the device that could lead to improved operational lifetimes.