Efficient electron injection layer for thermal stability of top emission phosphorescent organic light emitting diodes

Thermal stability holds significant importance in both high-resolution and large-area organic light-emitting diodes (OLEDs) due to its potential impacts on pixel shrinkage, thereby adversely affecting visual quality and long-term device functionality. The thermal instability could be from the thermal diffusion of metal ions or small molecules occurring at the interface between the electron injection layer (EIL) and the cathode material, influenced by differing surface properties and binding strength. In this study, we meticulously engineered magnesium fluoride (MgF₂) as EIL to mitigate the aforementioned challenges. Important physical properties associated with the EIL/cathode interaction were systematically analyzed. Employing Ag:Yb (2.5:1) as the cathode, we achieved notable enhancements in current efficiency and a reduced turn-on voltage for a green device operating under optical microcavity conditions. Thermal degradation test conducted over 240 h on fabricated devices revealed that employing MgF₂ as the EIL markedly enhanced thermal stability compared to devices utilizing Yb as the EIL reference. The robust EIL/cathode system observed herein is attributed to the high binding energy between the EIL and cathode materials utilized in this study.