The effects of reverse-bias on the current-voltage (I -V) and luminance-voltage (L -V) properties of organic light-emitting diodes ͑OLEDs͒ 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

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... cy 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 (t 01 ϭ17.9 s, t 02 ϭ507 s, t 03 ϭ7169 s) exist in the voltage shift process for ITO/TPD/Alq 3 /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.