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15 Feb 2010

Volume 96, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 96, 072501 (2010); http://dx.doi.org/10.1063/1.3314301 (3 pages)

T. Hesjedal and T. Phung
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Effects of concentrated sunlight on organic photovoltaics

Thomas Tromholt, Eugene A. Katz, Baruch Hirsch, Alexis Vossier, and Frederik C. Krebs

Appl. Phys. Lett. 96, 073501 (2010); http://dx.doi.org/10.1063/1.3298742 (3 pages) | Cited 22 times

Online Publication Date: 16 February 2010

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We report the effects of concentrated sunlight on key photovoltaic parameters and stability of organic photovoltaics (OPV). Sunlight collected and concentrated outdoors was focused into an optical fiber and delivered onto a 1 cm2 bulk-heterojunction cell. Sunlight concentration C was varied gradually from 0.2 to 27 suns. Power conversion efficiency exhibited slow increase with C that was followed by saturation around 2% at C = 0.5–2.5 suns and subsequent strong reduction. Possible OPV applications in stationary solar concentrators (C ≤ 2 suns) are discussed. Finally, experiments at C = 55–58 suns demonstrated potential of our approach for accelerated studies of light induced mechanisms in the OPV degradation.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells

Material quality requirements for efficient epitaxial film silicon solar cells

Kirstin Alberi, Ina T. Martin, Maxim Shub, Charles W. Teplin, Manuel J. Romero, Robert C. Reedy, Eugene Iwaniczko, Anna Duda, Paul Stradins, Howard M. Branz, and David L. Young

Appl. Phys. Lett. 96, 073502 (2010); http://dx.doi.org/10.1063/1.3309751 (3 pages) | Cited 16 times

Online Publication Date: 16 February 2010

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The performance of 2-μm-thick crystal silicon (c-Si) solar cells grown epitaxially on heavily doped wafer substrates is quantitatively linked to absorber dislocation density. We find that such thin devices have a high tolerance to bulk impurities compared to wafer-based cells. The minority carrier diffusion length is about half the dislocation spacing and must be roughly three times the absorber thickness for efficient carrier extraction. Together, modeling and experimental results provide design guidelines for film c-Si photovoltaic cells.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Db Elemental semiconductors and insulators

Organic field effect transistors from triarylamine side-chain polymers

Sven Hüttner, Michael Sommer, Ullrich Steiner, and Mukundan Thelakkat

Appl. Phys. Lett. 96, 073503 (2010); http://dx.doi.org/10.1063/1.3300464 (3 pages) | Cited 7 times

Online Publication Date: 17 February 2010

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We present a comparative study of organic field effect transistors (OFET) based on amorphous side-chain p-type polymers obtained from controlled radical polymerization. The side-chain moieties consist of different triarylamines such as triphenylamine, dimethoxytriphenylamine, and dimethoxytriphenyldiamine (DMTPD). The DMTPD-based polymer shows the highest OFET performance with mobilities of 10−4 cm2/V s. Furthermore, we show that the electrical properties are independent of the molecular weight due to the all-amorphous character of these side-chain polymers.
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85.30.Tv Field effect devices

Passive switching of electromagnetic devices with memristors

Matthew G. Bray and Douglas H. Werner

Appl. Phys. Lett. 96, 073504 (2010); http://dx.doi.org/10.1063/1.3299020 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2010

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A method of using memristors as passive electromagnetic switches is demonstrated via full-wave finite-difference time-domain simulations. A memristor is a fundamental circuit element that directly links flux and charge. These circuit elements exhibit a resistive memory effect, which results from a frequency dependent hysteresis. Therefore a memristor can be used as a resistive switch whose resistance varies under low frequency excitation but is unchanged at high frequencies. Utilizing this property, a passive reconfigurable band-pass frequency selective surface that is switched via space waves was designed and simulated.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
02.70.Bf Finite-difference methods
85.80.-b Thermoelectromagnetic and other devices

Near-IR activity of hybrid solar cells: Enhancement of efficiency by dissociating excitons generated in PbS nanoparticles

Asim Guchhait, Arup K. Rath, and Amlan J. Pal

Appl. Phys. Lett. 96, 073505 (2010); http://dx.doi.org/10.1063/1.3292183 (3 pages) | Cited 10 times

Online Publication Date: 18 February 2010

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Photovoltaic devices based on PbS nanoparticles remained inactive in the near-IR region due to a not-so-favorable energy band-diagram that does not allow dissociation of excitons generated in PbS. In this work, with the introduction of TiO2 nanostructures in the PbS-based hybrid system, we show an enhancement of photovoltaic performance in both visible and near-IR regions. The addition of TiO2 increases the power conversion efficiency from 0.006% to 0.12%. With the aid of energy band-diagram, we show that excitons generated in PbS even in the near-IR range can now become dissociated to yield photocurrent in the external circuit.
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88.40.H- Solar cells (photovoltaics)

Multimode transmission in complementary plasmonic structures at terahertz frequencies

Zhongxiang Zhang, Kam Tai Chan, Yanxia Cui, Sailing He, Changlei Wang, Qirong Xing, and Qingyue Wang

Appl. Phys. Lett. 96, 073506 (2010); http://dx.doi.org/10.1063/1.3318464 (3 pages) | Cited 1 time

Online Publication Date: 18 February 2010

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A three-dimensional subwavelength structure with periodic complementary metal patterns operating in the terahertz range has been proposed and fabricated. The device clearly exhibits three transmission modes under normal incidence, where experimental results obtained by terahertz time domain spectroscopy and simulated results agree very well with each other. The multimode transmission characteristics are found to arise from both localized coupling of fields between the interacting layers and propagating surface waves due to Bloch excitations on the surface of the periodic structure.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Resistive interlayer for improved performance of thin film silicon solar cells on highly textured substrate

M. Despeisse, G. Bugnon, A. Feltrin, M. Stueckelberger, P. Cuony, F. Meillaud, A. Billet, and C. Ballif

Appl. Phys. Lett. 96, 073507 (2010); http://dx.doi.org/10.1063/1.3324704 (3 pages) | Cited 26 times

Online Publication Date: 19 February 2010

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The deposition of thin-film silicon solar cells on highly textured substrates results in improved light trapping in the cell. However, the growth of silicon layers on rough substrates can often lead to undesired current drains, degrading performance and reliability of the cells. We show that the use of a silicon oxide interlayer between the active area and the back contact of the cell permits in such cases to improve the electrical properties. Relative increases of up to 7.5% of fill factor and of 6.8% of conversion efficiency are shown for amorphous silicon cells deposited on highly textured substrates, together with improved yield and low-illumination performance.
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88.40.jj Silicon solar cells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors

Proposed monolithic triple-junction solar cell structures with the potential for ultrahigh efficiencies using II–VI alloys and silicon substrates

Dong Xu, Tom Biegala, Michael Carmody, James W. Garland, Christoph Grein, and Sivalingam Sivananthan

Appl. Phys. Lett. 96, 073508 (2010); http://dx.doi.org/10.1063/1.3309410 (3 pages) | Cited 4 times

Online Publication Date: 19 February 2010

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The efficiencies of monolithic single-crystal II–VI and III–V, two-junction and three-junction solar cells are calculated. The structures consist of II–VI or III–V homojunctions grown on an active-junction substrate (silicon for II–VI and germanium for III–V) and of inverted three-junction II–VI or III–V structures, with the band gaps chosen to maximize the efficiencies. Our calculations for the II–VI cells give theoretical efficiencies up to 44% under 1 sun and 50% under 500 suns, ∼ 3% absolute higher than for the III–V cells. Maximum obtainable laboratory and production-line efficiencies for multijunction II–VI cells are predicted. Preliminary laboratory results for II–VI two-junction cells are also presented.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Technique to evaluate the diode ideality factor of light-emitting diodes

Hisashi Masui, Shuji Nakamura, and Steven P. DenBaars

Appl. Phys. Lett. 96, 073509 (2010); http://dx.doi.org/10.1063/1.3318285 (3 pages) | Cited 2 times

Online Publication Date: 19 February 2010

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A photoluminescence technique has been demonstrated on InGaN/GaN light-emitting diodes (LEDs) to evaluate their diode ideality factors. Selectively excited active regions produce potential differences between two contact terminals in addition to luminescence, from which the rate of recombination and terminal voltage have been related. Obtained ideality factors on commercial LEDs were between 1.1 and 2.4, which were significantly smaller than values determined via current–voltage characteristics. The ideality factor has been discussed from the viewpoint of direct-band-gap light-emitting pn junctions, and the notion that quantum-well structure takes over the role of the recombination plane introduced by the Sah–Noyce–Shockely analysis is proposed.
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85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Reduced electric field in junctionless transistors

Jean-Pierre Colinge, Chi-Woo Lee, Isabelle Ferain, Nima Dehdashti Akhavan, Ran Yan, Pedram Razavi, Ran Yu, Alexei N. Nazarov, and Rodrigo T. Doria

Appl. Phys. Lett. 96, 073510 (2010); http://dx.doi.org/10.1063/1.3299014 (3 pages) | Cited 20 times

Online Publication Date: 19 February 2010

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The electric field perpendicular to the current flow is found to be significantly lower in junctionless transistors than in regular inversion-mode or accumulation-mode field-effect transistors. Since inversion channel mobility in metal-oxide-semionductor transistors is reduced by this electric field, the low field in junctionless transistor may give them an advantage in terms of current drive for nanometer-scale complementary metal-oxide semiconductor applications. This observation still applies when quantum confinement is present.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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