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Recent development in colloidal quantum dots photovoltaics
Li PENG, Jiang TANG, Mingqiang ZHU
Front Optoelec. 2012, 5 (4): 358-370.
https://doi.org/10.1007/s12200-012-0285-7
The increasing demand for sustainable and green energy supply spurred the surging research on high-efficiency, low-cost photovoltaics. Colloidal quantum dot solar cell (CQDSC) is a new type of photovoltaic device using lead chalcogenide quantum dot film as absorber materials. It not only has a potential to break the 33% Shockley-Queisser efficiency limit for single junction solar cell, but also possesses low-temperature, high-throughput solution processing. Since its first report in 2005, CQDSCs experienced rapid progress achieving a certified 7% efficiency in 2012, an averaged 1% efficiency gain per year. In this paper, we reviewed the research progress reported in the last two years. We started with background introduction and motivation for CQDSC research. We then briefly introduced the evolution history of CQDSC development as well as multiple exciton generation effect. We further focused on the latest efforts in improving the light absorption and carrier collection efficiency, including the bulk-heterojunction structure, quantum funnel concept, band alignment optimization and quantum dot passivation. Afterwards, we discussed the tandem solar cell and device stability, and concluded this article with a perspective. Hopefully, this review paper covers the major achievement in this field in year 2011–2012 and provides readers with a concise and clear understanding of recent CQDSC development.
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Recent progress on tandem structured dye-sensitized solar cells
Dehua XIONG, Wei CHEN
Front Optoelec. 2012, 5 (4): 371-389.
https://doi.org/10.1007/s12200-012-0283-9
Tandem structured dye-sensitized solar cells (DSSCs) can take full advantage of sunlight, effectively broadening the absorption spectrum of the cell, resulting in a higher open circuit voltage or short circuit current than that of the conventional DSSC with single light absorber. The theoretical maximum efficiency is therefore suggested to be over the Schottky-Queisser limit of 33%. Accordingly, tandem design of DSSC is thought to be a promising way to break the performance bottleneck of DSSC. Besides, the tandem designs also broaden the application diversity of DSSC technology, which will accelerate its scale-up industrial application. In this paper, we have reviewed the recent progress on photo-electrochemical applications associated with kinds of tandem designs of DSSCs, in general, which are divided into three kinds: “n-type DSSC+n-type DSSC,” “n-type DSSC+p-type DSSC” and “n-type DSSC+other solar conversion devices.” The working principles, advantages and challenges of these tandem structured DSSCs have been discussed. Some possible solutions for further studies have been also pointed out together.
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Simple solutions for photonic power-efficient ultra-wideband system assisted by electrical bandpass filter
Jianji DONG, Yuan YU, Bowen LUO, Dexiu HUANG, Xinliang ZHANG
Front Optoelec. 2012, 5 (4): 403-413.
https://doi.org/10.1007/s12200-012-0281-y
We propose and experimentally demonstrate two simple solutions for power-efficient ultra-wideband (UWB) radio frequency (RF) system assisted by an electrical bandpass filter (EBPF). In the first solution, any optical Gaussian pulse with enough bandwidth is transmitted over optical fiber link, and then converted to a power-efficient UWB pulse by an EBPF with a passband of 3.1–10.6 GHz. The transmission and modulation of UWB signal is processed in optical domain, whereas the generation of UWB is processed in electrical domain. Both UWB modulations of on-off keying (OOK) and binary phase shift keying (BPSK) are experimentally demonstrated. In the second solution, the EBPF is used to convert any electrical waveform to a power-efficient UWB pulse. Then the electrical UWB pulse is converted to an optical UWB pulse with a Mach-Zehnder modulator (MZM), and then distributed over long haul fiber link. These two solutions embody the advantages of both low-loss long-haul transmission of optical fiber and mature electrical circuits. And the millimeter-wave UWB signal is also demonstrated.
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Competition mechanism of multiple four-wave mixing in highly nonlinear fiber: spatial instability and satellite characteristics
Liang ZHAO, Junqiang SUN, Xinliang ZHANG, Cong CHEN
Front Optoelec. 2012, 5 (4): 414-428.
https://doi.org/10.1007/s12200-012-0280-z
Competition mechanism in multiple four-wave mixing (MFWM) processes is demonstrated theoretically. Provided considering only two waves injected into a highly nonlinear fiber (HNLF), there are three modes displaying comprehensive dynamic behaviors, such as fixed points, periodic motion, and chaotic motion. Especially, Mode C of MFWM is emphasized by analyzing its phase-space trajectory to demonstrate nonlinear wave-wave interactions. The study shows that, when the phase-space trajectory approaches or gets through a saddle point, a dramatic power depletion for the injected wave can be realized, with the representative point moving chaotically, but when phase-space trajectories are distributed around a center point, the power for the injected wave is retained almost invariable, with the representative point moving periodically. Finally, the evolvement of satellite wave over an optical fiber is investigated by comparing it with the interference pattern in Young’s double-slit experiment.
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Heterogeneous photocatalytic treatment of wastewater in ultraviolet light irradiation—photocatalyst Bi2WO6 microsphere with high repeatability
Xiaojing Lu, Yin PENG, Zhengzheng HAN
Front Optoelec. 2012, 5 (4): 439-444.
https://doi.org/10.1007/s12200-012-0291-9
The treatment of wastewater that includes toxic organic pollutants such as dyes, phenoaniline, phenols and their derivatives is still a challenge due to their biorecalcitrant and acute toxicity to the widespread acceptance of water recycling. Three-dimensional (3D) Bi2WO6 microsphere was synthesized by the hydrothermal method using Bi(NO3)3 and Na2WO4 as raw materials. This structure exhibits high photocatalytic activity for the dyes, toxic organic compounds. The degradation of methlyene blue is 100% in 30 min, 4-nitrylphenol is 95% in 60 min and p-nitrylphenol is 95% in 75 min in ultraviolet (UV) light irradiation. 3D Bi2WO6 microsphere is also a good photocatalyst to treat the printing and dyeing sewage, and exhibits high repeatability. After being used the 20th time, Bi2WO6 still has high activity to degrade the printing and dyeing sewage, which is very important for a photocatalyst to be used in industry. This study will pave a new way to treat industry wastewater.
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Homogeneous and inhomogeneous broadening effects on static and dynamic responses of quantum-dot semiconductor optical amplifiers
Hussein TALEB, Kambiz ABEDI
Front Optoelec. 2012, 5 (4): 445-456.
https://doi.org/10.1007/s12200-012-0288-4
In this paper, the effects of homogeneous and inhomogeneous broadenings on the response of quantum-dot semiconductor optical amplifier (QD-SOAs) are investigated. For the first time, the state space model is used to simulate static and dynamic characteristics of the QD-SOA. It is found that with decreasing the homogeneous and inhomogeneous broadenings, the saturation power of the QD-SOA decreases and the optical gain and the ultrafast gain compression increase. Simulation results show that with decreasing the homogeneous broadening from 20 to 1 meV, the gain compression increases from 40% to 90%, the unsaturated optical gain becomes approximately tripled, and the saturation power becomes two times less. Also, simulations demonstrate that with decreasing the inhomogeneous broadening from 50 to 25 meV, the gain compression increases from less than 50% to more than 90%, the unsaturated optical gain becomes approximately 10-fold, and the saturation power becomes three times less. In addition, it is found that the homogeneous and inhomogeneous linewidths should be small for nonlinear applications. The homogeneous and inhomogeneous broadenings need to be large enough for linear applications.
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Proposal for modeling of tapered quantum-dot semiconductor optical amplifiers
Ehsan MOHADESRAD, Kambiz ABEDI
Front Optoelec. 2012, 5 (4): 457-464.
https://doi.org/10.1007/s12200-012-0289-3
To compensate for the loss of carrier density along the active region of quantum-dot semiconductor optical amplifiers (QD-SOAs), tapered structure of the waveguide is introduced. In this paper, a method for theoretically modeling of such devices is proposed, and according to that model different shapes of tapered waveguides are studied. This study is pivoted around the optical gain and cross-gain modulation (XGM) of the QD-SOA under investigation to show how altering the shape of the waveguide affects the main characteristics of the device. For doing so, the rate equation model has been employed and solved through finite difference method and MATLAB ODE. Through this, as long as monotonically increasing profiles for the width of the waveguide are used, the shape of the waveguide has a negligible effect on the gain which mainly depends on the width ratio of the waveguide output to its input. However, this carrier compensation has adverse effect on the XGM, where its efficiency rely on how the pump signal can effectively reduce carrier density and upset the gain.
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