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Electro-optic Ceramics and Devices
Published in Lionel M. Levinson, Electronic Ceramics, 2020
Although applicable to switching in general, photoassisted domain switching is usually thought of as the process by which image generation, storage, and erasure is achieved in PLZT image storage devices through selective switching. The three major effects that contribute to PDS include (1) photoexcitatiori of carriers both from trapping centers in the PLZT bandgap and across the bandgap by UV light of energy equal to or greater than the bandgap of 3.35 eV (lower energy, visible light can also photoexcite carriers from trapping centers in the handgap but with less efficiency); (2) carriers photoexeited to the conduction state diffuse (with no field applied) or drift under the influence of an applied field to new trapping sites beyond the absorption depth of the light, where they establish a space charge field that modulates the applied field and aids in the domain switching process by effectively lowering the coercive field of the material; and (3) photoexcited carriers, which are retrapped to establish the space charge field, result in a transient photocurrent, and carriers remaining in the conduction state contribute to a steady-state photovoltaic current driven by the bulk photovoltaic effect.
An Introduction to Photorefractive Polymers
Published in Hari Singh Nalwa, Seizo Miyata, Nonlinear Optics of Organic Molecules and Polymers, 2020
B. Kippelen, K. Meerholz, N. Peyghambarian
Another technique for the measurement of the photoconducting and transport properties of a material is the so-called time-of-flight technique shown in Figure 13. The polymer is coated on a transparent conducting electrode (typically ITO coated glass) and a metal electrode (Au, Ag, or Al) is evaporated on top of the polymer surface. Here, the sample can be identified with a capacitor having an optically transparent window. The capacitor is illuminated through this window and the absorbed light generates photocarriers which are collected by the metal electrode after transport through the sample. These collected carriers give rise to a photocurrent. This is detected by measuring the voltage across a resistor R placed after the sample in a circuit that contains also a voltage source. If the sample is excited with short light pulses with nanosecond duration, the mobility of the earners can be deduced from the shape of the transient photocurrent. For photoconductivity studies, the sample is excited with light pulses whose duration (typically 100 ms) is much longer than the transit time of the carriers in the material. Thus, quasi-steady-state excitation conditions can be assumed during light exposure. The pulsed excitation is preferred to a cw excitation in order to reduce internal space-charge formation effects. For the same reasons, the light intensity is kept at its lowest level. The photocurrent iPh and the photoconductivity ?(?)are given by:
Ultrafast Optical Pump-Probe Scanning Probe Microscopy/Spectroscopy
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Hidemi Shigekawa, Shoji Yoshida
To increase the generality of this microscopy technique and its applicability to various types of materials and structures, additional techniques are desired. For example, as an application of TR-STM based on a method similar to that used for the analysis of a molecular electronic structure, two-photon absorption measurement was used together with TR-STM (Wu & Ho 2010). For further advances in OPP-STM, the development of direct techniques for detecting photocur-rent in transient dynamics on the nanoscale is expected to play an important role in determining the optical characteristics of materials and devices. OPP-STM measurements of the transient photocurrent dynamics in the layered n-type semiconductor n-WSe2 have been carried out (Yoshida et al. 2013a, b). Since WSe2 has an indirect bulk band gap, the recombination lifetime of photoexcited carriers is significantly long (~10 μs) compared with the diffusion process. Therefore, under a forward bias voltage, i.e., a negative sample bias voltage, excited electrons are considered to directly tunnel to the STM tip as photocurrent, which has been clearly observed.
Enhanced photocatalytic hydrogen evolution by novel Nb-doped SnO2/V2O5 heteronanostructures under visible light with simultaneous basic red 46 dye degradation
Published in Journal of Asian Ceramic Societies, 2020
The transient photocurrent response experiments are carried out to further understand the efficient charge separation and an increased life-time of the charge carriers. Photocurrent measurements are often applied to qualitatively study the excitation and transfer of photogenerated electron/hole pairs in photocatalysts. Figure 7(b) presents the transient photocurrent curves of SnO2 nanotubes, SnO2/V2O5, 0.5, 1.0, 2.0, and 4.0 Nb-doped SnO2/V2O5 heteronanostructures recorded for repeated ON/OFF irradiation cycles under visible light. A slight photocurrent response (12 μA/cm2) is observed with the SnO2 nanotubes, whereas the photocurrent density reaches 23 μA/cm2 for SV heteronanostructure. As expected, Nb-doped SV heteronanostructures show a higher photocurrent intensity than SnO2 nanotubes and SV heteronanostructures. The 2.0Nb-SV sample exhibits the highest photocurrent density. In this case, the photocurrent upon irradiation rapidly increases to 46 μA/cm2 and then is stabilized at about 42 μA/cm2. When the light is turned off, the photocurrent drastically recovers to its initial level, indicating that the current is entirely photogenerated. The high photocurrent density can usually be ascribed to enhanced visible light absorption, as well as efficient charge migration and separation [41], which agrees well with the PL results. These results demonstrate that the Nb-doping combined with SnO2/V2O5 heterostructured nanocomposites can be an efficient strategy to promote photocatalytic properties.
Opto-electronic characterization of third-generation solar cells
Published in Science and Technology of Advanced Materials, 2018
Martin Neukom, Simon Züfle, Sandra Jenatsch, Beat Ruhstaller
In transient photocurrent (TPC) experiments the current response to a light step is measured at constant offset-voltage. The current rise and decay reveal information about the charge carrier mobilities, trapping and doping. TPC is usually performed with varied offset-voltage, offset-light or light pulse intensity. The rise time in organic solar cells usually lies between 1 and 100 μs. In perovskite solar cells, the current rise starts in the microsecond regime and can take several seconds until steady-state is reached [24].