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3 Sep 2012

Volume 101, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages)

Massimo Cuscunà, Annalisa Convertino, Emiliano Zampetti, Antonella Macagnano, Alessandro Pecora, Guglielmo Fortunato, Laura Felisari, Giuseppe Nicotra, Corrado Spinella, and Faustino Martelli
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Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

Christos Trompoukis, Ounsi El Daif, Valérie Depauw, Ivan Gordon, and Jef Poortmans

Appl. Phys. Lett. 101, 103901 (2012); http://dx.doi.org/10.1063/1.4749810 (4 pages) | Cited 4 times

Online Publication Date: 4 September 2012

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We report on the fabrication of two-dimensional periodic photonic nanostructures by nanoimprint lithography and dry etching and their integration into a 1-μm-thin mono-crystalline silicon solar cell. Thanks to the periodic nanopatterning, a better in-coupling and trapping of light is achieved, resulting in an absorption enhancement. The proposed light trapping mechanism can be explained as the superposition of a graded index effect and of the diffraction of light inside the photoactive layer. The absorption enhancement is translated into a 23% increase in short-circuit current, as compared to the benchmark cell, resulting in an increase in energy-conversion efficiency.
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88.40.jj Silicon solar cells
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors

Minimizing reflection losses from metallic electrodes and enhancing photovoltaic performance using the Si-micrograting solar cell with vertical sidewall electrodes

Tien-Chung Yang (楊天中), Bi-Shen Lee (李璧伸), and Ta-Jen Yen (嚴大任)

Appl. Phys. Lett. 101, 103902 (2012); http://dx.doi.org/10.1063/1.4749838 (5 pages)

Online Publication Date: 4 September 2012

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Researchers have focused on the development of Si nano- or micro-structured solar cells (SCs) because of their enhanced optical absorption properties and their ability to decouple minority carrier diffusion and light absorption paths. We adopt a low-cost method to monolithically fabricate Si-micrograting SC (SiMG-SC) with vertical sidewall electrodes and a vertical multi-junction, which minimizes the reflection losses from conventional planar metallic electrodes and increases the minority carrier collection probability. We consequently intensified the photovoltaic properties, i.e., the current density, fill factor, and power conversion efficiency, by 11.2%, 23.7%, and 52.9%, respectively, compared to those of the control SCs.
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88.40.hm Cost of production of solar cells
88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Analyzing nanotextured transparent conductive oxides for efficient light trapping in silicon thin film solar cells

Rahul Dewan, Jorj I. Owen, Darin Madzharov, Vladislav Jovanov, Jürgen Hüpkes, and Dietmar Knipp

Appl. Phys. Lett. 101, 103903 (2012); http://dx.doi.org/10.1063/1.4750242 (4 pages) | Cited 4 times

Online Publication Date: 4 September 2012

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Nanotextured contact layers are used in silicon thin film solar cells for increasing the short circuit current and conversion efficiency. We developed an approach to analyze random nanotextured surfaces by atomic force microscopy and image segmentation. It was used to investigate sputtered and wet chemically etched aluminum doped zinc oxide films with various morphologies. The information extracted from the surfaces was correlated with optical simulations of periodically textured thin film solar cells. The results from the surface analysis and optical simulations were also compared with the experimental results obtained for amorphous silicon solar cells prepared on the nanotextured substrates.
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88.40.jj Silicon solar cells
88.40.jm Thin film III-V and II-VI based solar cells
81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
68.55.jm Texture
88.40.hj Efficiency and performance of solar cells

On the minimum coupling required for maximum theoretical power capture from vibration energy harvesters

D. Kim, N. N. Hewa-Kasakarage, S. Yoon, and N. A. Hall

Appl. Phys. Lett. 101, 103904 (2012); http://dx.doi.org/10.1063/1.4749824 (3 pages)

Online Publication Date: 5 September 2012

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The minimum transducer coupling to enable maximum theoretical power capture from vibration energy harvesters is derived, leading to the simple conclusion that the product of the transducer coupling coefficient and resonance quality factor must be greater than two. Maximum theoretical power capture is experimentally demonstrated on a micromachined piezoelectric energy harvester comprised of a 20 μm thick epitaxial silicon cantilever with 800 nm thick lead-zirconate-titanate along the top surface and a bulk silicon mass at the tip. The coupling of these structures, although small (κ2 = 0.0033), is entirely sufficient to enable maximum theoretical power capture owing to light damping (Q = 906).
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07.10.Cm Micromechanical devices and systems

Flexoelectricity in several thermoplastic and thermosetting polymers

Baojin Chu and D. R. Salem

Appl. Phys. Lett. 101, 103905 (2012); http://dx.doi.org/10.1063/1.4750064 (4 pages) | Cited 2 times

Online Publication Date: 5 September 2012

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The flexoelectricity of several thermoplastic and thermosetting polymers was investigated by testing the dielectric polarization response under bending deformation of polymer cantilevers. All the polymers studied showed a flexoelectric response with a flexoelectric coefficient of the order of the 10−9–10−8 C/m. Based on a comparison of the flexoelectric response of the different polymers studied, we discuss factors that may influence the generation of flexoelectricity in polymeric materials.
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77.65.-j Piezoelectricity and electromechanical effects
77.22.Ej Polarization and depolarization
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
72.20.Pa Thermoelectric and thermomagnetic effects

Characterization of thin epitaxial emitters for high-efficiency silicon heterojunction solar cells

Bahman Hekmatshoar, Davood Shahrjerdi, Marinus Hopstaken, John A. Ott, and Devendra K. Sadana

Appl. Phys. Lett. 101, 103906 (2012); http://dx.doi.org/10.1063/1.4751339 (4 pages)

Online Publication Date: 6 September 2012

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We report silicon heterojunction solar cells with conversion efficiencies exceeding 21% using appropriately designed emitter structures comprised of highly doped thin epitaxial layers grown by plasma-enhanced chemical vapor deposition at temperatures close to 200 °C. We show that at a given doping concentration, there is an optimum epitaxial layer thickness, above which the conversion efficiency is limited by Auger recombination and bandgap narrowing within the epitaxial layer. In contrast, below the optimum thickness, the conversion efficiency is limited by carrier recombination at the emitter surface of the crystalline silicon substrate.
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88.40.jj Silicon solar cells
88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Strain induced lithium functionalized graphane as a high capacity hydrogen storage material

Tanveer Hussain, Abir De Sarkar, and Rajeev Ahuja

Appl. Phys. Lett. 101, 103907 (2012); http://dx.doi.org/10.1063/1.4751249 (5 pages) | Cited 3 times

Online Publication Date: 6 September 2012

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Strain effects on the stability, electronic structure, and hydrogen storage capacity of lithium-doped graphane have been investigated by state-of-the-art first principles density functional theory. Molecular dynamics simulations have confirmed the stability of Li on graphane sheet when it is subject to 10% of tensile strain. Under biaxial asymmetric strain, the binding energy of Li of graphane (CH) sheet increases by 52% with respect to its bulk’s cohesive energy. With 25% doping concentration of Li on CH sheet, the gravimetric density of hydrogen storage is found to reach up to 12.12 wt. %. The adsorption energies of H2 are found to be within the range of practical H2 storage applications.
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88.30.R- Hydrogen storage
71.20.Rv Polymers and organic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
02.70.Ns Molecular dynamics and particle methods
61.72.U- Doping and impurity implantation
68.43.Mn Adsorption kinetics

Intergrain variations of the chemical and electronic surface structure of polycrystalline Cu(In,Ga)Se2 thin-film solar cell absorbers

R. G. Wilks, I. Repins, M. A. Contreras, R. Félix, J. Herrero-Albillos, L. Tati-Bismaths, F. Kronast, R. Noufi, and M. Bär

Appl. Phys. Lett. 101, 103908 (2012); http://dx.doi.org/10.1063/1.4751261 (4 pages) | Cited 1 time

Online Publication Date: 6 September 2012

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The μm-scale spatial distribution of the elements of polycrystalline Cu(In1−xGax)Se2 absorber surfaces is examined using x-ray photoelectron emission microscopy. The chemical composition varies from grain to grain, and a direct, linear anticorrelation between the In 3d and Ga 2p photoemission line intensities is observed. The line intensities are interpreted in terms of a varying value of x= Ga/(In+ Ga); the band gaps calculated from the inferred compositions of the grains are shown to be normally distributed with a standard deviation of 40 meV.
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42.79.Ek Solar collectors and concentrators
88.40.jn Thin film Cu-based I-III-VI2 solar cells
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