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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.

With the existence of depletion layer, the intrinsic donor defect structure of ZnO ceramics has been investigated by broadband dielectric spectroscopy in a wide temperature range. Two loss peaks originating from electronic relaxation of oxygen vacancy and zinc interstitial, respectively, are observed in ZnO ceramics simultaneously, implying the coexistence of these two intrinsic defects. The corresponding activation energy for electronic relaxation of zinc interstitial and oxygen vacancy are 0.26 and 0.36eV, respectively, which is consistent with other reports

By using time-resolved electric-field-induced optical second-harmonic generation (EFISHG) measurement, we directly probed photovoltaic effect generated in double-layer (pentacene/C60) organic solar cells (OSCs). The electric field in C60 layer was selectively probed by using incident laser with a wavelength of 1,000 nm. Results showed that excess positive charges Qs=1.5×10-8 C/cm2 accumulated at the pentacene/C60 interface under photoillumination. These charges generated the interfacial voltage Vs=0.16 V and deformed a potential profile in the OSCs. The EFISHG measurement is an effective way for directly catching carrier behavior at the double-layer interface in OSCs in terms of the photovoltaic effect.