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22 Oct 2012

Volume 101, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 101, 171101 (2012); http://dx.doi.org/10.1063/1.4758996 (4 pages)

Wolfram H. P. Pernice and Harish Bhaskaran
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Enhanced photocurrent and conversion efficiency in thin-film microcrystalline silicon solar cells using periodically textured back reflectors with hexagonal dimple arrays

Hitoshi Sai (齋均), Kimihiko Saito (齊藤公彦), and Michio Kondo (近藤道雄)

Appl. Phys. Lett. 101, 173901 (2012); http://dx.doi.org/10.1063/1.4761956 (5 pages) | Cited 3 times

Online Publication Date: 22 October 2012

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Periodically textured back reflectors with hexagonal dimple arrays are applied to thin-film microcrystalline silicon (μc-Si:H) solar cells for enhancing their photon absorption and photovoltaic performance. In a systematic survey of 1 -μm-thick μc-Si:H cells, the best performance is obtained with a period of 1.5 μm and an aspect ratio of 0.20–0.25 with a high current density exceeding 26 mA/cm2 and a marked efficiency of 10.1%. These results demonstrate the high potential of periodic textures or surface gratings for improving the conversion efficiency of thin-film silicon solar cells.
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88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells
68.55.ag Semiconductors
79.60.-i Photoemission and photoelectron spectra

Nanowire array photovoltaics: Radial disorder versus design for optimal efficiency

Björn C. P. Sturmberg, Kokou B. Dossou, Lindsay C. Botten, Ara A. Asatryan, Christopher G. Poulton, Ross C. McPhedran, and C. Martijn de Sterke

Appl. Phys. Lett. 101, 173902 (2012); http://dx.doi.org/10.1063/1.4761957 (4 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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Solar cell designs based on disordered nanostructures tend to have higher efficiencies than structures with uniform absorbers, though the reason is poorly understood. To resolve this, we use a semi-analytic approach to determine the physical mechanism leading to enhanced efficiency in arrays containing nanowires with a variety of radii. We use our findings to systematically design arrays that outperform randomly composed structures. An ultimate efficiency of 23.75% is achieved with an array containing 30% silicon, an increase of almost 10% over a homogeneous film of equal thickness.
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88.40.hj Efficiency and performance of solar cells

Metamaterial particles for electromagnetic energy harvesting

Omar M. Ramahi, Thamer S. Almoneef, Mohammad Alshareef, and Muhammed S. Boybay

Appl. Phys. Lett. 101, 173903 (2012); http://dx.doi.org/10.1063/1.4764054 (5 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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Metamaterials are typically made of an ensemble of electrically small resonators such as metallic loops. The fact that such particles resonate individually to generate a bulk material behavior having enhanced constitutive parameters is essentially indicative of these particles' ability to collect energy. We show that such particles act as energy collectors when a resistive load is inserted within the particle's gap. A proof of concept is provided using a 5.8 GHz field and a split-ring resonator (SRR) as the electromagnetic energy collecting cell. Numerical simulation for a 9 × 9 SRR array shows the effectiveness of an SRR array as an energy collector plate.
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84.60.-h Direct energy conversion and storage
02.60.-x Numerical approximation and analysis

Limit on converted power in resonant electrostatic vibration energy harvesters

E. Blokhina, D. Galayko, P. Harte, P. Basset, and O. Feely

Appl. Phys. Lett. 101, 173904 (2012); http://dx.doi.org/10.1063/1.4764009 (4 pages)

Online Publication Date: 24 October 2012

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Based on the formal analysis of a resonant electrostatic vibration energy harvester operating in constant-charge mode with a gap-closing transducer, we show that the system displays universal behaviour patterns. In this paper, we treat the harvester as a nonlinear forced oscillator and bound the area of control parameters where the system displays regular harmonic oscillations allowing the conditioning circuit to operate in the most effective mode. Before the system exhibits irregular behaviour, there exists a universal optimal value of normalised converted power regardless of the system design and control parameters.
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84.60.-h Direct energy conversion and storage

The impact of commonly used approximations on the computation of the Seebeck coefficient and mobility of polar semiconductors

Ashok T. Ramu and John E. Bowers

Appl. Phys. Lett. 101, 173905 (2012); http://dx.doi.org/10.1063/1.4764517 (4 pages)

Online Publication Date: 25 October 2012

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Seebeck coefficient modeling and measurement has important applications in direct thermal to electrical energy conversion and solid-state physics. The computations of the Seebeck coefficient and mobility of polar semiconductors in the literature often employ certain approximations, notably the relaxation time approximation (RTA) and the truncation of the Boltzmann transport equation. We study the accuracy of these approximations as a function of the effective mass, temperature, and carrier concentration using a recently developed technique for rigorous solution of the Boltzmann transport equation. We find that the approximations give rise to considerable error in the computed Seebeck coefficients of heavily doped semiconductors with a low effective mass, and that the RTA is entirely inapplicable for the accurate computation of the mobility of several important materials.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Fr Low-field transport and mobility; piezoresistance
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