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Film Si Solar Cells with Nano Si: Cooperative Research and Development Final Report, CRADA Number CRD-09-00356

Description: Nevada Nanotechnology Center and Si group at NREL will work together to develop a-Si based solar cells with nano-Si technique. We will explore the existing a-Si based film solar cell technology at NREL and nano scale Si technology at Nevada Nanotechnology Center. By exchanging information, we will come; up with some new cell structures using nano-Si. We expect the new a-Si based cells will have optical enhancement or better electronic or optical properties of absorber layer to improve solar cell performance.
Date: May 1, 2011
Creator: Wang, Q.
Partner: UNT Libraries Government Documents Department

NREL Core Program; Session: Wafer Silicon (Presentation)

Description: This project supports the Solar America Initiative by working on: (1) wafer Si accounts for 92% world-wide solar cell production; (2) research to fill the industry R and D pipeline for the issues in wafer Si; (3) development of industry collaborative research; (4) improvement of NREL tools and capabilities; and (5) strengthen US wafer Si research.
Date: April 1, 2008
Creator: Wang, Q.
Partner: UNT Libraries Government Documents Department

Magnitude and value of electric vehicle emissions reductions for six driving cycles in four US cities with varying air quality problems

Description: The emissions of logically competing mid-1990 gasoline vehicles (GVs) and electric vehicles (EVs) are estimated as if the vehicles were driven in the same pattern of driving. Six different driving cycles are evaluated, ranging in speed from 7 to 49 miles per hour (mph). These steps are repeated using specifics of fuel composition, electric power mix, and environmental conditions applicable to Chicago, Denver, Los Angeles, and New York in the month of July. The year 2000 emissions differences for each of four regulated pollutants - HC, CO, NO{sub x,} SO{sub x} - are estimated. CO{sub 2} emissions are also estimated. With use of EVs, HC and CO emissions are consistently lowered by 98% or more. CO{sub 2} emissions reductions are uniformly large at low speed, but variable at high speed. It is found that initially introduced EVs could achieve 100% emission reductions in Chicago by using off-peak power from nuclear power plants for EV electricity generation. Emissions reductions occur for all combinations in Los Angeles, and for most combinations in New York, excepting SO{sub x}. NO{sub x} emissions are reduced in all four cities. An ``avoided cost`` value for each regulated pollutant is estimated for each of the cities. The values for each city depend on severity of air quality violations. It is estimated that the emissions reduction value of EVs driven an average of one and one half hours per day in Los Angeles ranges from $1050 to $3,900; $590 to $2100 in New York; $270 to $1200 in Chicago, and $330 to $1250 in Denver (1989$). Assuming a range of about 100 miles in congested conditions with speeds of 10 mph or less, the estimates range from $3600 to $13300 for Los Angeles; $2004 to $7200 for New York; $930 to $2930 for Chicago; and $1120 to $4290 ...
Date: December 31, 1992
Creator: Wang, Q. & Santini, D. L.
Partner: UNT Libraries Government Documents Department

Light Trapping for High Efficiency Heterojunction Crystalline Si Solar Cells: Preprint

Description: Light trapping plays an important role to achieve high short circuit current density (Jsc) and high efficiency for amorphous/crystalline Si heterojunction solar cells. Si heterojunction uses hydrogenated amorphous Si for emitter and back contact. This structure of solar cell posses highest open circuit voltage of 0.747 V at one sun for c-Si based solar cells. It also suggests that over 25% record-high efficiency is possible with further improvement of Jsc. Light trapping has two important tasks. The first one is to reduce the surface reflectance of light to zero for the solar spectrum that Si has a response. The second one is to increase the effective absorption length to capture all the photon. For Si heterojunction solar cell, surface texturing, anti-reflectance indium tin oxides (ITO) layer at the front and back are the key area to improve the light trapping.
Date: April 1, 2011
Creator: Wang, Q.; Xu, Y.; Iwaniczko, E. & Page, M.
Partner: UNT Libraries Government Documents Department

Nonlinear Legendre Spectral Finite Elements for Wind Turbine Blade Dynamics: Preprint

Description: This paper presents a numerical implementation and examination of new wind turbine blade finite element model based on Geometrically Exact Beam Theory (GEBT) and a high-order spectral finite element method. The displacement-based GEBT is presented, which includes the coupling effects that exist in composite structures and geometric nonlinearity. Legendre spectral finite elements (LSFEs) are high-order finite elements with nodes located at the Gauss-Legendre-Lobatto points. LSFEs can be an order of magnitude more efficient that low-order finite elements for a given accuracy level. Interpolation of the three-dimensional rotation, a major technical barrier in large-deformation simulation, is discussed in the context of LSFEs. It is shown, by numerical example, that the high-order LSFEs, where weak forms are evaluated with nodal quadrature, do not suffer from a drawback that exists in low-order finite elements where the tangent-stiffness matrix is calculated at the Gauss points. Finally, the new LSFE code is implemented in the new FAST Modularization Framework for dynamic simulation of highly flexible composite-material wind turbine blades. The framework allows for fully interactive simulations of turbine blades in operating conditions. Numerical examples showing validation and LSFE performance will be provided in the final paper.
Date: January 1, 2014
Creator: Wang, Q.; Sprague, M. A.; Jonkman, J. & Johnson, N.
Partner: UNT Libraries Government Documents Department

SIMS Study of Elemental Diffusion During Solid Phase Crystallization of Amorphous Silicon

Description: Crystallization of hydrogenated amorphous silicon (a-Si:H) films deposited on low-cost substrates shows potential for solar cell applications. Secondary ion mass spectrometry (SIMS) was used to study impurity incorporation, hydrogen evolution, and dopant diffusion during the crystallization process
Date: November 1, 2005
Creator: Reedy, R. C.; Young, D.; Branz, H. M. & Wang, Q.
Partner: UNT Libraries Government Documents Department

Efficient Crystalline Si Solar Cell with Amorphous/Crystalline Silicon Heterojunction as Back Contact: Preprint

Description: We study an amorphous/crystalline silicon heterojunction (Si HJ) as a back contact in industrial standard p-type five-inch pseudo-square wafer to replace Al back surface field (BSF) contact. The best efficiency in this study is over 17% with open-circuit (Voc) of 0.623 V, which is very similar to the control cell with Al BSF. We found that Voc has not been improved with the heterojunction structure in the back. The typical minority carrier lifetime of these wafers is on the order of 10 us. We also found that the doping levels of p-layer affect the FF due to conductivity and band gap shifting, and an optimized layer is identified. We conclude that an amorphous/crystalline silicon heterojunction can be a very promising structure to replace Al BSF back contact.
Date: June 1, 2012
Creator: Nemeth, B.; Wang, Q. & Shan, W.
Partner: UNT Libraries Government Documents Department

SIMS Characterization of Amorphous Silicon Solar Cells Grown by Hot-Wire Chemical Vapor Deposition on Stainless Steel

Description: This paper is intended to be an overview of some of the challenges that must be overcome when characterizing amourphous-silicon solar cell devices by the secondary ion mass spectrometry (SIMS) technique.
Date: January 1, 2000
Creator: Reedy, R. C.; Wang, Q.; Moutinho, H.; Iwaniczko, E. & Mahan, A. H.
Partner: UNT Libraries Government Documents Department

X-ray flashes in ROSAT PSPC data

Description: The authors find 24 short (200--2,500s) X-ray flashes from all the ROSAT Position Sensitive Proportional Counter (PSPC) observations above galactic latitude 30 degrees ({approximately} 9.6 Msec) and some observations toward low latitudes ({approximately} 2.4 Msec). The brightest flash is quite extraordinary. Its flux rises from nondetection by a factor of > 200 in less than 100 sec. Its spectrum can be fitted either by a thermal plasma model with kT {ge} 2.4 keV, or by a single power-law with the photon number index of {approx} {minus}1.7. Photon statistics are not sufficient to obtain spectra for other flashes. The flash event fields can vary from optically crowded regions to blank fields. Although eight flashes are found from observations from nearby galaxies, and three of them are within the optical extent of their corresponding galaxies, they could not statistically establish that there are two different populations between nearby galaxies and control fields.
Date: December 1, 1998
Creator: Sun, X.; Li, H.; Fenimore, E.E. & Wang, Q.D.
Partner: UNT Libraries Government Documents Department

Research on high-band-gap materials and amorphous-silicon-based solar cells. Annual subcontract report, May 15, 1994--May 14, 1995

Description: We have conducted a survey of thin BP:H and BPC:H films prepared by plasma deposition using phosphine, diborane, tri-methylboron, and hydrogen as precursor gases. The objective of this research is to find out whether such films might offer a superior window layer film for application to wide bandgap a-Si solar cells. The research has shown good optical properties in a-BP:H films, but electrical properties acceptable for use in window layers have not been demonstrated yet. We have also found an interesting, conductive and transparent BPC:H film in a remote deposition region of the reactor, but have been unable to transfer deposition of this film to the standard interelectrode region. We have developed our capability to deposit nip sequence amorphous silicon based solar cells, and have demonstrated an open circuit voltage greater than 0.7 V. We have continued our studies of built-in potentials in a-Si based solar cells using the electroabsorption technique, extending our measurements to include cells with wider bandgap intrinsic layers and Schottky barrier test structures. We have made the first time-of-flight drift mobility measurements on a-Si:H prepared by hot wire (HW) deposition. Initial work has shown that light-soaked HW material can have much better ambipolar diffusion lengths than the plasma-deposited material following extended light soaking. We have performed some theoretical work which addresses a difficulty in understanding photocarrier recombination in a-Si:H first identified by Marvin Silver. In particular, electron-hole recombination is much slower than expected from the well-known {open_quotes}diffusion-controlled{close_quotes} models for Onsager (geminate) recombination and Langevin recombination. This slowness is essential to the success of a-Si in solar cells, but is unexplained. We have done work on high field electron drift mobilities in a-Si:H and on the validity of the Einstein relation connecting the diffusion and drift of holes in a-Si:H.
Date: December 1, 1995
Creator: Schiff, E.A.; Gu, Q.; Jiang, L. & Wang, Q.
Partner: UNT Libraries Government Documents Department

Process Optimization for High Efficiency Heterojunction c-Si Solar Cells Fabrication Using Hot-Wire Chemical Vapor Deposition: Preprint

Description: The researchers extensively studied the effects of annealing or thermal history of cell process on the minority carrier lifetimes of FZ n-type c-Si wafers with various i-layer thicknesses from 5 to 60 nm, substrate temperatures from 100 to 350 degrees C, doped layers both p- and n-types, and transparent conducting oxide (TCO).
Date: June 1, 2012
Creator: Ai, Y.; Yuan, H. C.; Page, M.; Nemeth, W.; Roybal, L. & Wang, Q.
Partner: UNT Libraries Government Documents Department

Performance of Hydrogenated a-Si:H Solar Cells with Downshifting Coating: Preprint

Description: We apply a thin luminescent downshifting (LDS) coating to a hydrogenated amorphous Si (a-Si:H) solar cell and study the mechanism of possible current enhancement. The conversion material used in this study converts wavelengths below 400 nm to a narrow line around 615 nm. This material is coated on the front of the glass of the a-Si:H solar cell with a glass/TCO/p/i/n/Ag superstrate configuration. The initial efficiency of the solar cell without the LDS coating is above 9.0 % with open circuit voltage of 0.84 V. Typically, the spectral response below 400 nm of an a-Si:H solar cell is weaker than that at 615 nm. By converting ultraviolet (UV) light to red light, the solar cell will receive more red photons; therefore, solar cell performance is expected to improve. We observe evidence of downshifting in reflectance spectra. The cell Jsc decreases by 0.13 mA/cm2, and loss mechanisms are identified.
Date: May 1, 2011
Creator: Nemeth, B.; Xu, Y.; Wang, H.; Sun, T.; Lee, B. G.; Duda, A. et al.
Partner: UNT Libraries Government Documents Department

Atomic Structure and Electronic Properties of c-Si/a-Si:H Interfaces in Si Heterojunction Solar Cells

Description: The atomic structure and electronic properties of crystalline silicon/hydrogenated amorphous silicon (c-Si/a-Si:H) interfaces in silicon heterojunction (SHJ) solar cells are investigated by high-resolution transmission electron microscopy, atomic-resolution Z-contrast imaging, and electron energy loss spectroscopy. We find that all high-performance SHJ solar cells exhibit atomically abrupt and flat c-Si/a-Si:H interfaces and high disorder of the a-Si:H layers. These atomically abrupt and flat c-Si/a-Si:H interfaces can be realized by direct deposition of a-Si:H on c-Si substrates at a substrate temperature below 150 deg C by hot-wire chemical vapor deposition from pure silane.
Date: November 1, 2005
Creator: Yan, Y.; Page, M.; Wang, Q.; Branz, H. M.; Wang, T. H. & Al-Jassim, M. M.
Partner: UNT Libraries Government Documents Department

FTIR Laboratory in Support of the PV Program

Description: The Fourier Transform Infrared Spectroscopy (FTIR) Laboratory supports the Solar Energy Technologies Program through the measurement and characterization of solar energy-related materials and devices. The FTIR technique is a fast, accurate, and reliable method for studying molecular structure and composition. This ability to identify atomic species and their bonding environment is a powerful combination that finds use in many research and development efforts. A brief overview of the technical approach used is contained in Section 2 of this report. Because of its versatility and accessibility, the FTIR Laboratory is a valuable contributor to the Solar Energy Technologies Program. The laboratory provides support for, and collaborates with, several in-house programs as well as our industry and university partners. By the end of FY 2004, the FTIR Laboratory performed over 1100 measurements on PV-related materials. These contributions resulted in conference and workshop presentations and several peer-reviewed publications. A brief summary of a few of these efforts is contained in Section 3 of this report.
Date: January 1, 2005
Creator: Keyes, B. M.; Gedvilas, L. M.; Bhattacharya, R.; Xu, Y.; Li, X. & Wang, Q.
Partner: UNT Libraries Government Documents Department

Real-Time Spectroscopic Ellipsometry as an In-Situ Diagnostic for Hot-Wire CVD Growth of Amorphous and Epitaxial Si

Description: Real-time spectroscopic ellipsometry (RTSE) has proven to be an exceptionally valuable tool in the optimization of hot wire CVD (HWCVD) growth of both silicon heterojunction (SHJ) solar cells and thin epitaxial layers of crystal silicon (epi-Si). For SHJ solar cells, RTSE provides real-time thickness information and rapid feedback on the degree of crystallinity of the thin intrinsic layers used to passivate the crystal silicon (c-Si) wafers. For epi-Si growth, RTSE provides real-time feedback on the crystallinity and breakdown of the epitaxial growth process. Transmission electron microscopy (TEM) has been used to verify the RTSE analysis of thickness and crystallinity. In contrast to TEM, RTSE provides feedback in real time or same-day, while TEM normally requires weeks. This rapid feedback has been a key factor in the rapid progress of both the SHJ and epi-Si projects.
Date: January 1, 2005
Creator: Levi, D.; Teplin, C.; Iwaniczko, E.; Wang, T.; Wang, Q.; Yan, Y. et al.
Partner: UNT Libraries Government Documents Department

Research on defects and transport in amorphous silicon-based semiconductors

Description: This report describes the results from research on two topics: (1) the effects of light-soaking on the electron drift mobility in a-Si:H, and (2) modulated electron spin resonance measurements and their relationship to the electronic correlation energy of the D center in a-Si:H. Both of these projects were undertaken to better determine where the standard'' model for a-Si:H breaks down. The standard model is reasonably successful in accounting for the most elementary deep trapping'' aspects of electron and hole transport in a-Si:H, and it accounts adequately for the sub-band-gap optical properties. However, it is much less clear whether it provides a sufficient basis for understanding several effects which are crucial in operating solar cells: electron and hole mobilities and recombination in the presence of light-bias and space-charge. In the standard model, one would not expect significant effects on drift mobilities due to light-soaking, which would be envisioned as simply increasing the D-center density. Similarly, in the standard model one would not anticipate a significant temperature dependence to electron spin resonance, because essentially all spins are already detected. Discussions in the available literature on the evidence regarding both effects were inconclusive. The work reported here sets considerably more stringent constraints on the magnitude of the two effects.
Date: April 1, 1992
Creator: Schiff, E.A.; Antoniadis, H.; Lee, J.K. & Wang, Q. (Syracuse Univ., NY (United States))
Partner: UNT Libraries Government Documents Department

Well-Passivated a-Si:H Back Contacts for Double-Heterojunction Silicon Solar Cells: Preprint

Description: We have developed hydrogenated amorphous silicon (a Si:H) back contacts to both p- and n-type silicon wafers, and employed them in double-heterojunction solar cells. These contacts are deposited entirely at low temperature (<250 C) and replace the standard diffused or alloyed back-surface-field contacts used in single-heterojunction (front-emitter only) cells. High-quality back contacts require excellent surface passivation, indicated by a low surface recombination velocity of minority-carriers (S) or a high open-circuit voltage (Voc). The back contact must also provide good conduction for majority carriers to the external circuit, as indicated by a high light I-V fill factor. We use hot-wire chemical vapor deposition (HWCVD) to grow a-Si:H layers for both the front emitters and back contacts. Our improved a-Si:H back contacts contribute to our recent achievement of a confirmed 18.2% efficiency in double-heterojunction silicon solar cells on p type textured silicon wafers.
Date: May 1, 2006
Creator: Page, M. R.; Iwaniczko, E.; Xu, Y.; Wang, Q.; Yan, Y.; Roybal, L. et al.
Partner: UNT Libraries Government Documents Department

Crystal Silicon Heterojunction Solar Cells by Hot-Wire CVD: Preprint

Description: Hot-wire chemical vapor deposition (HWCVD) is a promising technique for fabricating Silicon heterojunction (SHJ) solar cells. In this paper we describe our efforts to increase the open circuit voltage (Voc) while improving the efficiency of these devices. On p-type c-Si float-zone wafers, we used a double heterojunction structure with an amorphous n/i contact to the top surface and an i/p contact to the back surface to obtain an open circuit voltage (Voc) of 679 mV in a 0.9 cm2 cell with an independently confirmed efficiency of 19.1%. This is the best reported performance for a cell of this configuration. We also made progress on p-type CZ wafers and achieved 18.7% independently confirmed efficiency with little degradation under prolong illumination. Our best Voc for a p-type SHJ cell is 0.688 V, which is close to the 691 mV we achieved for SHJ cells on n type c-Si wafers.
Date: May 1, 2008
Creator: Wang, Q.; Page, M. R.; Iwaniczko, E.; Xu, Y. Q.; Roybal, L.; Bauer, R. et al.
Partner: UNT Libraries Government Documents Department

Photoconductive Decay Lifetime and Suns-Voc Diagnostics of Efficient Heterojunction Solar Cells: Preprint

Description: We report results of minority carrier lifetime measurements for double-sided p-type Si heterojunction devices and compare Suns-Voc results to Light I-V measurements on 1 cm2 solar cell devices measured on an AM1.5 calibrated XT-10 solar simulator.
Date: May 1, 2008
Creator: Page, M. R.; Iwaniczko, E.; Xu, Y.; L., Roybal; Bauer, R.; Yan, H.-C. et al.
Partner: UNT Libraries Government Documents Department

Silicon Solar Cells with Front Hetero-Contact and Aluminum Alloy Back Junction: Preprint

Description: We prototype an alternative n-type monocrystalline silicon (c-Si) solar cell structure that utilizes an n/i-type hydrogenated amorphous silicon (a-Si:H) front hetero-contact and a back p-n junction formed by alloying aluminum (Al) with the n-type Si wafer.
Date: May 1, 2008
Creator: Yuan, H.-C.; Page, M. R.; Iwaniczko, E.; Xu, Y.; Roybal, L.; Wang, Q. et al.
Partner: UNT Libraries Government Documents Department