Direct identification of interfacial degradation in blue phosphorescent OLEDs using nanoscale chemical depth profiling

Abstract Understanding the degradation mechanism of organic light-emitting diodes (OLED) is essential to improve device performance and stability. OLED failure, if not process-related, arises mostly from chemical instability. However, the challenges of sampling from nanoscale organic layers and interfaces with enough analytical information has hampered identification of degradation products and mechanisms. Here, we present a high-resolution diagnostic method of OLED degradation using an Orbitrap mass spectrometer equipped with a gas cluster ion beam to gently desorb nanometre levels of materials, providing unambiguous molecular information with 7-nm depth resolution. We measured blue phosphorescent OLED devices and showed that dominant chemical degradation occurred at the interface between electron transport and emission layers (EML/ETL) where exciton distribution was maximised. We also show an approximately two orders of magnitude increase in lifetime of a device with slightly modified host material, which presented negligible EML/ETL interfacial degradation. Our results provide insight for material and device architecture development.