Analysis of thermal degradation of bis(2-phenylpyridine) (acetylacetonate)iridium(III) (Ir(ppy)2(acac)) using spectroelectrochemistry.

Abstract

Enhancing the lifespan of organic light-emitting diodes (OLEDs) is crucial for developing stable, high-performance devices. The operational lifetime and performance of OLEDs are reportedly primarily enhanced by the thermal and chemical stability of their constituent single molecules. Therefore, understanding the thermal and electrical stability of these organic molecules is essential for long-lifetime OLED fabrication. However, the degradation of these materials during thermal evaporation has not yet been evaluated. In this study, we investigated the thermal degradation of bis(2-phenylpyridine) (acetylacetonate)iridium(III) (Ir(ppy)₂(acac)), a widely used green phosphorescent dopant, using spectroelectrochemistry (SEC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectroscopy techniques. SEC measurements revealed the ability of the Ir(ppy)₂(acac) molecules to exhibit different polaron states before and after thermal aging. Gaussian fitting showed the presence of additional polaron absorption peaks in the SEC spectra, which indicated that degradation occurred gradually over the first 4 h of aging and then saturated. MALDI-TOF analysis confirms these results, showing an additional peak at 622.9 m/z, corresponding to thermally aged Ir(ppy)₂(acac), alongside the intrinsic molecule peak at 599.8 m/z. This result suggested that the Ir(ppy)₂(acac) ligand underwent thermal aging-induced degradation in the deposition chamber. Through this study, we anticipate contributing to related research and industrial advancement by enabling the rapid evaluation of the thermal degradation of OLED materials.