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23 Jul 2012

Volume 101, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 043101 (2012); http://dx.doi.org/10.1063/1.4737152 (4 pages)

Toshiaki Tanigaki, Yoshikatsu Inada, Shinji Aizawa, Takahiro Suzuki, Hyun Soon Park, Tsuyoshi Matsuda, Akira Taniyama, Daisuke Shindo, and Akira Tonomura
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Zn migration during spark plasma sintering of thermoelectric Zn4Sb3

Hao Yin (殷浩), Mogens Christensen, Nina Lock, and Bo B. Iversen

Appl. Phys. Lett. 101, 043901 (2012); http://dx.doi.org/10.1063/1.4731764 (3 pages) | Cited 3 times

Online Publication Date: 23 July 2012

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The phase homogeneity of spark plasma sintered thermoelectric Zn4Sb3 pellets along the pressing direction has been studied by potential Seebeck microprobe scanning and spatially resolved x-ray diffraction. Significant variations in the Seebeck coefficient reflect presence of different crystalline phases. The emergence of the ZnSb phase at the bottom of the pellet and metallic Zn impurity at the top explains the variation in the Seebeck coefficients. Quantitative phase distributions along the pressing axis were determined from the Rietveld refinements of spatially resolved x-ray diffraction patterns. These reveal a migration of highly mobilized Zn atoms under the direct current applied during spark plasma sintering.
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72.20.Pa Thermoelectric and thermomagnetic effects
52.77.-j Plasma applications
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.80.Jc Other crystalline inorganic semiconductors

Theoretical limits for visibly transparent photovoltaics

Richard R. Lunt

Appl. Phys. Lett. 101, 043902 (2012); http://dx.doi.org/10.1063/1.4738896 (4 pages) | Cited 1 time

Online Publication Date: 24 July 2012

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Transparent photovoltaics (PVs) provide a potentially facile route to building-integrated PVs and seamless energy-harvesting within non-window surfaces such as electronic displays, autonomously powered electronic-glazings, and mobile-electronic accessories. Such devices have been enabled by manipulation of excitons in organic and molecular semiconductors that allow for selective ultraviolet and near-infrared solar conversion. Here, the theoretical efficiency limits of transparent photovoltaics are determined as a function of transparency. Power-production from ultraviolet and near-infrared photons alone leads to a theoretical single-junction efficiency of 21% in transparent structures, compared to 33% for opaque-junctions. Reducing thermal losses via transparent multi-junction stacking these limits increase to 37%.
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88.40.hj Efficiency and performance of solar cells

Fluctuations in photocurrent of bulk heterojunction polymer solar cells—A valuable tool to understand microscopic and degradation processes

Monojit Bag, N. S. Vidhyadhiraja, and K. S. Narayan

Appl. Phys. Lett. 101, 043903 (2012); http://dx.doi.org/10.1063/1.4738985 (5 pages)

Online Publication Date: 24 July 2012

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We report electrical noise measurements from illuminated bulk heterojunction (BHJ) polymer based solar cells (PSC). These noise-studies of BHJ-PSCs provide considerable insight into the underlying charge transport processes. The power spectrum reveals a flicker noise of the form 1/fα at low frequencies (f < 1 kHz) while an unusual log-normal feature is observed in the f-regime >5 kHz. Photocurrent fluctuations were analyzed at different temperature, light intensity, and device conditions. A theoretical description employing kinetic Monte-Carlo simulations points to the importance of trap distribution and kinetics in the understanding of fluctuations in the low f regime.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells

Strain-free ring-shaped nanostructures by droplet epitaxy for photovoltaic application

Jiang Wu, Zhiming M. Wang, Vitaliy G. Dorogan, Shibin Li, Zhihua Zhou, Handong Li, Jihoon Lee, Eun Soo Kim, Yuriy I. Mazur, and Gregory J. Salamo

Appl. Phys. Lett. 101, 043904 (2012); http://dx.doi.org/10.1063/1.4738996 (4 pages) | Cited 10 times

Online Publication Date: 25 July 2012

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Droplet epitaxy is a flexible nanomaterial growth technique and is a potential method to fabricate advanced electronic and optoelectronic devices. Here, we report strain-free GaAs/Al0.33Ga0.67As quantum ring solar cells fabricated by droplet epitaxy technique. Photoluminescence is used to study the electronic structure of the lattice-matched GaAs/Al0.33Ga0.67As quantum ring solar cells. Post-growth thermal annealing is used to improve the optical quality of the solar cell as well as device efficiency. A power conversion efficiency of 1.8% is demonstrated from a prototype quantum ring solar cell. This work opens new opportunities for quantum dot solar cells with strain-free nanostructures.
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88.40.jm Thin film III-V and II-VI based solar cells
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials

Giant augmentations in electro-hydro-dynamic energy conversion efficiencies of nanofluidic devices using viscoelastic fluids

Aditya Bandopadhyay and Suman Chakraborty

Appl. Phys. Lett. 101, 043905 (2012); http://dx.doi.org/10.1063/1.4739429 (4 pages) | Cited 2 times

Online Publication Date: 26 July 2012

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We report a mechanism of massive augmentations in energy harvesting capabilities of nanofluidic devices, through the combined deployment of viscoelastic fluids and oscillatory driving pressure forces. Our analyses demonstrate that when the forcing frequency of a pressure-driven flow matches with the inverse of the relaxation time scale of a typical viscoelastic fluid, the energy conversion efficiency may get giantly amplified because of a complex interplay between the fluid rheology and ionic transport within the electrical double layer, which may open up the realm of highly efficient operating regimes of electro-hydrodynamic energy conversion in nanofluidic devices of practical relevance.
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07.10.Cm Micromechanical devices and systems
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
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