Degradation of blue phosphorescent organic LEDs analyzed by solution NMR spectroscopy

In organic light-emitting diodes (OLEDs), device degradation is one of the crucial problems to be solved. In this study, we have investigated material degradations in FIrpic-based phosphorescent OLEDs by solution nuclear magnetic resonance (NMR) spectroscopy. NMR experiments clearly indicate that about 18% of TPhDB molecules, which is used as an electron-transporting material, are decomposed during driving the devices. The decomposition of the TPhDB molecules is considered to be related to the device degradation. This study demonstrates that solution NMR spectroscopy is a useful tool to investigate an origin of device degradation of multi-layered OLEDs in terms of decomposition of organic molecules.