Impact of high voltage on the performance of high-contrast-ratio organic light emitting devices

The role of ultra-thin buffer layer of C₆₀ in recently developed high contrast-ratio tandem organic light emitting devices (HCT-OLEDs) is experimentally investigated. The strong photon emission of Al/C₆₀/ N, N´-di(naphthalene-1-yl)- N, N´- diphenylbenzidine/tris8-hydroxyquinoline-aluminum/LiF/Al verifies the efficient hole-injecting role of Al (7 nm)/C₆₀ (2.5 nm). When the applied voltage is higher than 15 V, abrupt drop in current is experienced and the peak of the electroluminescence spectrum vanishes as a result of the phase tuning structure of the HCT-OLED. This demonstrates that the Al/C₆₀ anode performance is unstable under high voltage operation. Such instability causes HCT-OLED power efficiency to drop significantly, necessitating more stable buffer layers to be used instead of C₆₀ in order to realise viable HCT-OLEDs for display applications.