A two-step polarization reversal process was identified in the pentacene/poly(vinylidene fluoride-trifluoroethylene) double-layer device. Displacement current measurement showed that three peaks generated non-symmetrically in the current-voltage characteristics. Accordingly, optical electric-field induced second-harmonic generation measurement displayed two hysteresis loops. A proposed model based on a two-step polarization reversal mechanism accounted for these results, and suggested that interaction of interfacial charge and ferroelectric polarization governed the mechanism. The proposed model is useful to explain the reduced remanent polarization in ferroelectric field-effect transistors, and will be helpful for developing organic devices with a ferroelectric layer.

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.

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.

Summary This work considers an input and output constraint control problem for pure‐feedback systems with nonaffine functions possibly being in‐differentiable. A locally semibounded and continuous condition for nonaffine functions is presented to guarantee the controllability, and the nonaffine system is transformed to an equivalent pseudoaffine one based on the mild condition. Combined with backstepping technique, a novel prescribed performance controller with new performance functions is constructed to circumvent high frequency chattering in control input. An auxiliary system with bounded compensation term is utilized in this paper, successfully avoiding the overrun of control input. The methodology achieves the desired transient and steady‐state performance and presents excellent robustness against the system uncertainty. Finally, two numerical simulations are performed to demonstrate the effectiveness of the proposed approach.

By using time-resolved electric field induced second harmonic generation, we directly probed interfacial charging and discharging in double-layer devices with an indium tin oxide (ITO)/polyimide(PI)/N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD) (or pentacene)/Au structure, where PI serves as a blocking layer. The results showed that carriers injected from Au electrodes were responsible for interfacial charging and discharging, but different carrier behaviors were observed for pentacene and α-NPD devices, which implies that two devices have the different electrical properties. By analyzing the devices as a system of a Maxwell–Wagner effect element, we proposed a model that accounted for the difference in the charging and discharging processes in terms of carrier behavior.