Chemical degradation processes of highly stable red phosphorescent organic light emitting diodes

We investigate the chemical degradation processes of highly stable red organic light emitting diodes (OLEDs) based on the triplet emitter tris(1-phenylisoquinoline)iridium(III) by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS). The analysis of LDI-TOF spectra, collected on OLEDs driven at different current densities, shows a direct correlation between the lifetime of the devices and the formation of the three different reaction products: a BPhen dimer, an adduct of BPhen dimer with cesium, and the complex BAlq₂ + Al(Me-q)₂]⁺ as well. Additionally it was possible to identify another degradation product, whose chemical structure is related to the α-NPD molecule as well to the fluorine of the used p-dopant. This product is only observable in devices aged at very high current densities.