Oxygen, relative humidity, and interlayer related issues in organic electronics

Residual levels of O2 in OLEDs and their relation to device performance were evaluated by measuring (1) the photoluminescence (PL) decay time (following pulsed UV LED excitation) of the O2 sensing dye Pd octaethylporphyrin (PdOEP) doped in the active OLED layer poly(Nvinylcarbazole) (PVK) and (2) the electroluminescence (EL) decay time (following a bias pulse) of glass/ITO/PEDOT:PSS/6 wt.% PdOEP:PVK/CsF/Al OLEDs. The active layer was prepared under various conditions of exposure to controlled O2 levels and relative humidity. PdOEP was used successfully for monitoring exposure of PdOEP:PVK to low levels of oxygen and shortened device PL decay times often indicated device deterioration. The PL decay time at various applied voltages and the EL decay time at various current densities were monitored to evaluate degradation processes related to oxygen and other bimolecular quenching phenomena. 2.