Effect of Duty Ratio of Driving Voltage on the Forming Process in Aging of Organic Electroluminescent Device*

An interesting phenomenon “forming process”, namely, the rising process of luminance and efficiency at the initial aging of organic eletroluminescent devices, was studied under constant pulse voltage excitation with different duty ratios. The device has a conventional double-layer structure. Tris(8-quinolinolato) aluminum (Alq) was used as the emitter layer, and poly(N-vinylcarbazole) (PVK) was used as the hole transport layer (HTL). The increase of luminance is due to that of the current. It was assumed that the forming process results from the redistribution of the electric field in the organic layer due to the build up of space charge at the interfaces as well as other factors.