An organic light-emitting diode (OLED) was analyzed as a system of the Maxwell-Wagner effect element, by using time-resolved optical second harmonic generation (SHG) measurement. A transient SHG signal generated fromlayer in an indium zinc oxide (IZO)/R-NPD/tris(8-hydroxy-quinolinato) aluminum(III) (Alq3)/ LiF/Al OLED device was selectively probed with applying alternating current (AC) square wave voltage, and the electric field distribution change in the device was examined. Results showed that charge Q s at the R-NPD/Alq3 interface changed in accordance with charging and discharging processes accompanied by electroluminescence (EL). We found that observed SHG response reflected well charging and discharging of carriers on electrodes and carrier transit across R-NPD and Alq3 layers, and accounted for nonreversal charging and discharging processes.

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