Passivation of organic light-emitting diodes by the plasma polymerized para-xylene thin film

Plasma-polymerized para-xylene (PPpX) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) were used to passivate the organic light-emitting diodes (OLEDs). For OLEDs, indium-tin-oxide, N,N'-diphenyl-N,N'-bis(3-methylphenyl)- 1,1'-diphenyl-4,4'-diamine tris-8-hydroxyquinoline aluminum and aluminum were used as the anode, the hole transport layer, the emitting layer and the cathode, respectively. The OLED device with the PPpX passivation film (passivated device) showed similar electrical and optical characteristics to those of the OLED device without the PPpX passivation film (control device), indicating that the PECVD process did not degrade the performance of the OLEDs notably. Although PPpX passivation did not enhance the lifetime of the OLEDs significantly, the PPpX film was, to some extent, effective as a passivation layer of the OLEDs. The lifetime of the passivated device was two times longer than that of the control device. Passivation of OLEDs with PPpX films also suppressed the growth of dark spots. The density and size of dark spots of the passivated device were much smaller than those of the control device.