Voltage shift phenomena introduced by reverse-bias application in multilayer organic light emitting diodes

The effects of reverse-bias on the current–voltage (I–V) and luminance–voltage (L–V) properties of organic light-emitting diodes (OLEDs) were systematically measured. Shifts toward lower voltage both in I–V and L–V curves were observed for the OLEDs treated by reverse-bias application. The voltage-shift phenomena were discussed based on the effective drive voltage change induced by reverse bias application and the voltage-shift process was analyzed by using a relaxation model. Good consistency between experimental results and model calculations was obtained. It was found that the voltage shift process has several time constants. For example, three time constants (t₀₁=17.9 s, t₀₂=507 s, t₀₃=7169 s) exist in the voltage shift process for ITO/TPD/Alq₃/Mg:Ag diodes. The voltage shifts are assumed to be closely related to the movement of ionic impurities and rotations of permanent dipoles in organic layers. © 2000 American Institute of Physics.