Impact of the LiF/Al/Au and stacked phase tuning layers on the viewing angle of high contrast-ratio tandem organic light emitting devices

The impact of a LiF/Al/Au composite layer on both electrical performance and optical performance of high contrast-ratio tandem organic light emitting devices (HCT-OLEDs) operating in wide viewing angle regimes is investigated. The strong photon emission from Al/Au/ NPB(N,N´-di(naphthalene-1-yl)- N,N´-diphenylbenzidine) /Alq₃(tris8-hydroxyquinoline-aluminum)/LiF/Al and the symmetrical current-voltage curve for Al/LiF/Alq₃/LiF/Al verify the hole-injecting anodic and the electron-injecting cathodic roles of Al(4 nm)/Au(7 nm) and Al(4 nm)/LiF(0.7 nm), respectively. The reflectivity spectrum is measured for viewing angles ranging from 5° to 50°. Experimental results show that when the viewing angle is increased from 5° to 50°, the reflectivity spectrum is blue shifted, which affects the contrast of HCT-OLEDs. Importantly, the measured average reflectivity in the visible range for viewing angles below 50° is as low as 6.6%, making the proposed HCT-OLEDs attractive for flat-panel-display applications.