2,008 research outputs found
Charge mobility determination by current extraction under linear increasing voltages: the case of non-equilibrium charges and field-dependent mobilities
The method of current extraction under linear increasing voltages (CELIV)
allows for the simultaneous determination of charge mobilities and charge
densities directly in thin films as used in organic photovoltaic cells (OPV).
In the past, it has been specifically applied to investigate the interrelation
of microstructure and charge transport properties in such systems. Numerical
and analytical calculations presented in this work show that the evaluation of
CELIV transients with the commonly used analysis scheme is error prone once
charge recombination and, possibly, field dependent charge mobilities are taken
into account. The most important effects are an apparent time-dependence of
charge mobilities and errors in the determined field dependencies. Our results
implicate that reports on time-dependent mobility relaxation in OPV materials
obtained by the CELIV technique should be carefully revisited and confirmed by
other measurement methods.Comment: 15 pages, 9 figure
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Nanowire Photoelectrochemistry.
Recent applications of photoelectrochemistry at the semiconductor/liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run
Evaluation of ambipolar carrier mobility in alkyl-substituted phthalocyanine thin film
Yuki Nishikawa, Yuya Nakata, Shigehiro Ikehara, Akihiko Fujii, and Masanori Ozaki "Evaluation of ambipolar carrier mobility in alkyl-substituted phthalocyanine thin film," Journal of Photonics for Energy 8(3), 032214 (15 May 2018). DOI: https://doi.org/10.1117/1.JPE.8.03221
Metal oxide semiconducting interfacial layers for photovoltaic and photocatalytic applications
The present review rationalizes the significance of the metal oxide semiconductor (MOS) interfaces in the field of photovoltaics and photocatalysis. This perspective considers the role of interface science in energy harvesting using organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs). These interfaces include large surface area junctions between photoelectrodes and dyes, the interlayer grain boundaries within the photoanodes, and the interfaces between photoactive layers and the top and bottom contacts. Controlling the collection and minimizing the trapping of charge carriers at these boundaries is crucial to overall power conversion efficiency of solar cells. Similarly, MOS photocatalysts exhibit strong variations in their photocatalytic activities as a function of band structure and surface states. Here, the MOS interface plays a vital role in the generation of OH radicals, which forms the basis of the photocatalytic processes. The physical chemistry and materials science of these MOS interfaces and their influence on device performance are also discussed
Solution-Processed Phototransistors Combining Organic Absorber and Charge Transporting Oxide for Visible to Infrared Light Detection.
This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 1012 Jones under a low power illumination of 20 nW/cm2, outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
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