Probing of interfacial charging and discharging in double-layer devices with a polyimide blocking layer by time-resolved optical second harmonic generation (original) (raw)
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IEICE Transactions on Electronics, 2011
The Maxwell-Wagner type interfacial charging processes were characterized by time-resolved second harmonic generation method (TR-SHG) using three typical organic double-layer devices, i.e., IZO/α-NPD/Alq3/Al for OLED and ITO/PI/α-NPD (or pentacene)/Au for MIM elements. Devices with a PI blocking layer represent one-carrier transport case, while the OLED is a typical two-carrier transport device. It is found that three devices show similar behavior of charging of the electrodes, however, interfacial charging behavior was different from case to case. On the basis of Maxwell-Wagner model, the different transients were analyzed with consideration of carrier species responsible for the interfacial charging. The observed TR-SHG well support the results of I-V measurements. key words: organic double-layer device, TR-SHG, interfacial charging, MW effect
Japanese Journal of Applied Physics, 2011
By using time-resolved electric-field-induced optical second-harmonic generation (TR-EFISHG) measurements, we studied the voltage establishment in an indium tin oxide (ITO)/polyimide/pentacene/Au double-layer device in terms of Maxwell-Wagner type charging and discharging. Results showed that the voltage establishment and relaxation in the pentacene layer depend on the polarity of the applied voltage, suggesting different carrier behaviors of electrons and holes in the pentacene layer. The interfacial relaxation time ( MW ) also showed a different voltage dependence on the carrier species. A computer simulation using the relaxation time ratio T r ð¼ RC = MW Þ well accounts for the results.
Chemical Physics Letters, 2011
Optical electric field induced second-harmonic generation (EFISHG) measurement was applied to investigate interfacial carrier charging in pentacene/C 60 double-layer organic solar cells (OSCs) in terms of photovoltaic effect. The EFISHG measurements demonstrated that electrode charging and interfacial charging at the pentacene/C 60 interface produce electric fields with opposite directions in the C 60 layer. Making use of OSCs connected to various resistances R e showed that the two charging processes exhibit opposite changing tendency due to the photovoltaic (PV) effect, while the response time of the both two charging processes increase with the increases of R e . The Maxwell-Wagner model analysis well accounted for the results obtained using EFISHG measurements.
Journal of Applied Physics, 2011
The voltage dependent Maxwell-Wagner (MW) type interfacial carrier relaxation process in a fullerene(C 60 )/polyimide double-layer device was studied by using time-resolved second harmonic generation technique (TR-SHG). The charging of the electrodes, carrier transport, interfacial charge accumulation, and relaxation processes were revealed individually by TR-SHG and analyzed on the basis of the MW model. However, it was found that the interfacial carrier relaxation process followed a stretched exponential law and had a higher order dependence on the applied voltage, which cannot be explained by the simple MW model and were attributed to the bulk traps distributed in the fullerene layer. By taking into account the effects of bulk traps, a bulk-trap modulated MW model was proposed. This model indicates that the interfacial carrier relaxation time (s MW ) is not only voltage dependent, but also time dependent, especially within the time region comparable to the characteristic relaxation time of the bulk traps (s t ). It is suggested that the two-variable dependent s MW (V ex ,t) is responsible for the observed experiment results.
Investigation of the interfacial electronic properties of N,N'-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bisdicarboximide (PDI8-CN2) organic semiconductor films grown on silicon dioxide is performed by polarization-resolved second harmonic generation optical spectroscopy, pointing out a spatial region where charge carriers distribution in the semiconductor lacks inversion symmetry. By developing a model for nonlinear susceptibility in the framework of Debye-Huckel screening theory, we show that the experimental findings can be interpreted as resulting from the presence of a net charge localized at the silicon dioxide, accompanied by a non-uniform charge distribution in the organic semiconductor. Photoluminescence analysis further reinforces this scenario. Reduction-oxidation reactions involving PDI8-CN2 and water molecules are invoked as physical origin of the localized charge. The work outlines a sensitive tool to probe the total charge localized at buried semiconductor/d...
Japanese Journal of Applied Physics, 2011
By using electric-field-induced second-harmonic generation (EFISHG) measurement, we probed charging and discharging in an -NPD/Alq3 organic light-emitting diode N,-N,N 0 -diphenyl]-(1,1 0 -biphenyl)-4,4 0 -diamine; Alq3, tris(8-hydroxy-quinolinato)aluminum(III)] while electroluminescence response was monitored. The EFISHG measurement showed that excessive positive charges accumulated at the -NPD/Alq3 interface in the charging process, accompanying electroluminescence (EL) radiation, and the accumulated excess positive charges disappeared in the discharging process before the EL decayed. Note that the EL radiation was smooth and strong under the high voltage application, while the EL decayed in a similar way. The Maxwell-Wagner model analysis showed no-dependence of the accumulated excessive positive charge on the applied external voltage, suggesting that electrons and holes injected from the opposite electrodes for EL radiation balanced at the interface. The EFISHG measurement will be useful as a direct way to probe carrier behaviors in organic EL devices.
Physics Procedia, 2011
By using time-resolved optical second harmonic generation (TR-SHG) measurements, we studied carrier behaviors in poly(3hexylthiophene) (P3HT) metal-insulator-semiconductor (MIS) diodes. TR-SHG measurements probed transients of electric field distribution in the P3HT active layer. Results showed that hole injection and removal processes were non-reversal, where the response times were different from each other and the relaxation time of the transient electric field strongly depended on the hole injection process.
Japanese Journal of Applied Physics, 2012
The channel formation process in a pentacene field effect transistor was studied by directly probing the carrier motion along the channel in the time domain and the capacitance changes in the frequency domain. With the source and drain electrodes short circuited and the voltage applied only to the gate electrode, the carrier injection from both top electrodes and its motion along the channel was still observable, implying an interface charging process driven by a self-induced electric field. In addition, it was found that when the source and drain electrodes were short circuited, the capacitance of the device was larger than the geometric capacitance and proportional to the channel length, which also supported the interface charging model. The relationship between the two approaches was also discussed. #