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Amorphous and Thin-Film Silicon

Description: This paper outlines the key concepts set forth in the Amorphous and Thin-Film Silicon session at the National Center for Photovoltaics and Solar Program Review Meeting held March 26, 2003 in Denver, Colorado. Key elements of discussion centered around benchmarking the NREL/NCPV amorphous and thin-film silicon program, identifying holes in the scientific understanding of these materials and devices, identifying hurdles to large scale manufacturing, and what direction the program should take for future activities.
Date: May 1, 2003
Creator: Nelson, B. P.; Atwater, H. A.; von Roedern, B.; Yang, J.; Sims, P.; Deng, X. et al.
Partner: UNT Libraries Government Documents Department

The future of amorphous silicon photovoltaic technology

Description: Amorphous silicon modules are commercially available. They are the first truly commercial thin-film photovoltaic (PV) devices. Well-defined production processes over very large areas (>1 m{sup 2}) have been implemented. There are few environmental issues during manufacturing, deployment in the field, or with the eventual disposal of the modules. Manufacturing safety issues are well characterized and controllable. The highest measured initial efficiency to date is 13.7% for a small triple-stacked cell and the highest stabilized module efficiency is 10%. There is a consensus among researchers, that in order to achieve a 15% stabilized efficiency, a triple-junction amorphous silicon structure is required. Fundamental improvements in alloys are needed for higher efficiencies. This is being pursued through the DOE/NREL Thin-Film Partnership Program. Cost reductions through improved manufacturing processes are being pursued under the National Renewable Energy Laboratory/US Department of Energy (NREL/DOE)-sponsored research in manufacturing technology (PVMaT). Much of the work in designing a-Si devices is a result of trying to compensate for the Staebler-Wronski effect. Some new deposition techniques hold promise because they have produced materials with lower stabilized defect densities. However, none has yet produced a high efficiency device and shown it to be more stable than those from standard glow discharge deposited material.
Date: June 1, 1995
Creator: Crandall, R. & Luft, W.
Partner: UNT Libraries Government Documents Department

Amorphous and Microcrystalline Silicon Solar Cells: Preprint

Description: We review the progress made by amorphous silicon solar cells, including the emerging technology of solar cells of microcrystalline silicon. The long-term trend in the efficiency of stabilized laboratory cells based on a-Si:H has been a rise of {approx}0.6 % per year. The recent trend in the a-Si,Ge:H cell efficiency alone, measured in the spectral window assigned to the bottom device in a triple-junction cell, has been an increase of {approx}0.16% per year. These improvements have brought within reach the target of 15% efficiency identified by EPRI and DOE for widespread application. Our review leads to an identification of areas of promising research, with emphasis on the fundamental science required to reach the 15% target, and then to move to the next-level efficiency goal.
Date: April 1, 1999
Creator: Wagner, S. (Princeton University); Carlson, D. E. (Solarex) & Branz, H. M. (National Renewable Energy Laboratory)
Partner: UNT Libraries Government Documents Department

Amorphous Silicon Based Neutron Detector

Description: Various large-scale neutron sources already build or to be constructed, are important for materials research and life science research. For all these neutron sources, neutron detectors are very important aspect. However, there is a lack of a high-performance and low-cost neutron beam monitor that provides time and temporal resolution. The objective of this SBIR Phase I research, collaboratively performed by Midwest Optoelectronics, LLC (MWOE), the University of Toledo (UT) and Oak Ridge National Laboratory (ORNL), is to demonstrate the feasibility for amorphous silicon based neutron beam monitors that are pixilated, reliable, durable, fully packaged, and fabricated with high yield using low-cost method. During the Phase I effort, work as been focused in the following areas: 1) Deposition of high quality, low-defect-density, low-stress a-Si films using very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) at high deposition rate and with low device shunting; 2) Fabrication of Si/SiO2/metal/p/i/n/metal/n/i/p/metal/SiO2/ device for the detection of alpha particles which are daughter particles of neutrons through appropriate nuclear reactions; and 3) Testing of various devices fabricated for alpha and neutron detection; As the main results: · High quality, low-defect-density, low-stress a-Si films have been successfully deposited using VHF PECVD on various low-cost substrates; · Various single-junction and double junction detector devices have been fabricated; · The detector devices fabricated have been systematically tested and analyzed. · Some of the fabricated devices are found to successfully detect alpha particles. Further research is required to bring this Phase I work beyond the feasibility demonstration toward the final prototype devices. The success of this project will lead to a high-performance, low-cost, X-Y pixilated neutron beam monitor that could be used in all of the neutron facilities worldwide. In addition, the technologies developed here could be used to develop X-ray and neutron monitors that could be used in ...
Date: December 12, 2004
Creator: Xu, Liwei
Partner: UNT Libraries Government Documents Department

Amorphous silicon PVMaT Phase 2A. Semiannual subcontract report, 1 May 1992--31 October 1992

Description: This report describes work done under a subcontract to significantly advance the photovoltaic manufacturing technologies, reduce module production costs, increase average module performance, and increase the production capacity existing at Utility Power Group (UPG) and Advanced Photovoltaic Systems, Inc. (APS). Areas of focus include (1) encapsulation and termination, (2) product design, (3) process and quality control, and (4) automation. UPG will improve its encapsulation system through the development of advanced encapsulation materials and processes that result in a module that does not require backing glass. In addition, UPG will work to develop advanced termination materials and processes. APS will perform development activities centered on the EUREKA manufacturing line. Developments in the APS EUREKA encapsulation system will be in addition to the UPG activity on encapsulation, and will offer an alternative approach to the problems of encapsulating large-area thin-film modules.
Date: September 1, 1993
Creator: Duran, G.; Mackamul, K.; Metcalf, D.; Stern, M.; Volltrauer, H.; Varar, T. et al.
Partner: UNT Libraries Government Documents Department

High Efficiency and High Rate Deposited Amorphous Silicon-Based Solar Cells: Final Technical Report, 1 September 2001--6 March 2005

Description: The objectives for the University of Toledo are to: (1) establish a transferable knowledge and technology base for fabricating high-efficiency triple-junction a-Si-based solar cells, and (2) develop high-rate deposition techniques for the growing a-Si-based and related alloys, including poly-Si, c-Si, a-SiGe, and a-Si films and photovoltaic devices with these materials.
Date: January 1, 2006
Creator: Deng, X.
Partner: UNT Libraries Government Documents Department

Thin-film amorphous silicon alloy research partnership. Final technical progress report, 2 February 1995--28 February 1998

Description: This report describes the status and accomplishments of work performed by United Solar Systems Corp. under this subcontract. Investigations were carried out on Ag/ZnO, Ag/TiO{sub 2}/ZnO and Ag/MgF{sub 2}/ZnO back reflectors to assess their suitability for use in cell structures. Arrays of high-efficiency component cells were made over 1-ft{sup 2} areas. Single-junction top cells were made with an average stabilized power density of 5.4 mW/cm{sup 2} measured under global AM1.5 illumination. Single-junction middle cells were optimized to give average stabilized power density of 3.6 mW/cm{sup 2} under global AM1.5 illumination with a cut-on filter with {lambda} > 530 nm. Arrays of high-efficiency triple-junction cells of 0.25-cm{sup 2} active area were fabricated over 1-ft{sup 2} area with average stabilized efficiency of 12% as measured under AM1.5 illumination. A triple-junction module of a 416-cm{sup 2} aperture area was fabricated with an initial efficiency of 11.7% and stabilized efficiency of 10.24%. A 922-cm{sup 2} aperture-area module exhibited an initial efficiency of 11.5%. The novel laser-drilling approach was used successfully to fabricate modules of 1-ft{sup 2} area with shadow loss of approximately 1%. Using this laser-drilling approach, an initial total-area efficiency of 11.5% was achieved in a triple-cell structure of 12.6 cm{sup 2} area. An initial total-area efficiency of 10.6% was achieved in a module of 300-cm{sup 2} area. Reliability studies based on NREL`s Interim Qualification Testing were carried out to confirm the suitability of the module encapsulation materials and processes. 29 figs., 17 tabs.
Date: May 1, 1998
Creator: Guha, S.
Partner: UNT Libraries Government Documents Department

Field collapse due to band-tail charge in amorphous silicon solar cells

Description: It is common for the fill factor to decrease with increasing illumination intensity in hydrogenated amorphous silicon solar cells. This is especially critical for thicker solar cells, because the decrease is more severe than in thinner cells. Usually, the fill factor under uniformly absorbed red light changes much more than under strongly absorbed blue light. The cause of this is usually assumed to arise from space charge trapped in deep defect states. The authors model this behavior of solar cells using the Analysis of Microelectronic and Photonic Structures (AMPS) simulation program. The simulation shows that the decrease in fill factor is caused by photogenerated space charge trapped in the band-tail states rather than in defects. This charge screens the applied field, reducing the internal field. Owing to its lower drift mobility, the space charge due to holes exceeds that due to electrons and is the main cause of the field screening. The space charge in midgap states is small compared with that in the tails and can be ignored under normal solar-cell operating conditions. Experimentally, the authors measured the photocapacitance as a means to probe the collapsed field. They also explored the light intensity dependence of photocapacitance and explain the decrease of FF with the increasing light intensity.
Date: May 1, 1996
Creator: Wang, Qi; Crandall, R.S. & Schiff, E.A.
Partner: UNT Libraries Government Documents Department

Progress in amorphous silicon PV technology: An update

Description: To reach the 15% stabilized efficiency goal for amorphous silicon (a-Si) modules by the year 2005, the National Renewable Energy Laboratory has established four research teams. The teams -- with members from industry, universities, and NREL -- have been in operation for 2.5 years now. Consensus has been reached that a triple-junction a-Si structure is needed to reach the efficiency goal. Performance parameter goals for the overall structure and the three component cells have been formulated. All four teams have generated their own development plans. Individual team progress relative to the plans is reported.
Date: July 1, 1995
Creator: Luft, W.; Branz, H.M.; Dalal, V.L.; Hegedus, S.S. & Schiff, E.A.
Partner: UNT Libraries Government Documents Department

Status of Amorphous and Crystalline Thin Film Silicon Solar Cell Activities

Description: This paper reviews the recent activities and accomplishments of the national Amorphous Silicon Team and a (crystalline) thin-film-Si subteam that was implemented in 2002 to research solar cell devices based on thin crystalline Si based layers. This paper reports the evolution of team organization, the technical highlights from the recent team meetings, and an outlook on commercialization potential.
Date: May 1, 2003
Creator: von Roedern, B.
Partner: UNT Libraries Government Documents Department

Project Summary of the NREL Amorphous Silicon Team

Description: The Amorphous Silicon Team at NREL has improved the properties of many materials, increased solar cell device performance, and improved the fundamental understanding of thin-film silicon based materials and devices since the last NCPV Program Review Meeting. In this paper we present a summary of the work of the team since that last meeting.
Date: May 1, 2003
Creator: Nelson, B. P.; Branz, H. M.; Crandall, R. S.; Iwaniczko, E.; Mahan, A. H.; Stradins, P. et al.
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

Photocharge transport and recombination measurements in amorphous silicon films and solar cells by photoconductive frequency mixing. Annual subcontract report, 15 May 1995--15 May 1996

Description: Using the photomixing technique, the authors systematically studied the transport properties of intrinsic hydrogenated amorphous silicon (a-Si:H) samples that had hydrogen content ranging from over 10% to less than 1% and which were produced by the hot-wire technique at NREL. They investigated the continuous decay of electron drift mobility in intrinsic a-Si:H on light-soaking and determined the degradation of photoconductivity, lifetime, and drift mobility in these a-Si:H samples while light-soaking. In addition to the decay of the photoconductivity and electron lifetime, continuous decay of the electron drift mobility was found during the light-soaking process, which reveals a new phenomenon associated with the Staebler-Wronski effect. The drift mobility decreased by a factor of 2--4 for 5-hour light-soaking at 4-sun intensity. The authors investigated the effects of deposition conditions on transport properties of intrinsic a-Si:H films and, by using the photomixing technique, they determined the electron drift mobility, lifetime, and the conduction-band Urbach energy of a-Si:H films as a function of substrate temperature. 44 refs.
Date: October 1, 1996
Creator: Braunstein, R. & Dong, S.
Partner: UNT Libraries Government Documents Department

Optical modeling of a-Si solar cells

Description: The authors describe applications of PV Optics to analyze the behavior of a metallic back-reflector on an a-Si solar cell. The calculated results from PV Optics agree well with the measured data on solar cells. Several unexpected results obtained from these calculations are qualitatively explained.
Date: November 4, 1999
Creator: Sopori, B.; Madjdpour, J.; Zhang, Y.; Chen, W.; Guha, S.; Yang, J. et al.
Partner: UNT Libraries Government Documents Department

Technical evaluation of a USSC Integrated/Direct Mount PV Roofing Module system at NREL

Description: The results of a 16 month technical evaluation performed on a nominal 1 kW{sub ac} utility-interconnect amorphous silicon PV system deployed at the National Renewable Energy Laboratory`s PV outdoor test site are given here. The system employs 64 prototype United Solar Systems Corp. Integrated/Direct Mount PV Roofing Modules mounted on simulated attic/roof structures. In this paper we show that the PV array fill factor has been relatively stable with respect to time and that the seasonal variations in performance can be largely attributed to seasonal variations in current. We also show that in determining the summer and winter ac power output, the summation of the manufacturer-supplied module peak powers at STC for a similarly located and configured a-Si PV array should be derated by factors of approximately of 0.83 and 0.78 for summer and winter operation, respectively.
Date: May 1, 1995
Creator: Strand, T.; Hansen, R. & Mrig, L.
Partner: UNT Libraries Government Documents Department

Baseline Evaluation of Thin-Film Amorphous Silicon, Copper Indium Diselenide, and Cadmium Telluride for the 21st Century: Preprint

Description: This paper examines three thin-film PV technologies: amorphous silicon, cadmium telluride, and copper indium selenide. The purpose is to: (1) assess their status and potential; (2) provide an improved set of criteria for comparing these existing thin films against any new PV technological alternatives, and examining the longer-term (c. 2050) potential of thin films to meet cost goals that would be competitive with conventional sources of energy without any added value from the substantial environmental advantages of PV. Among the conclusions are: (1) today's thin films have substantial economic potential, (2) any new approach to PV should be examined against the substantial achievements and potential of today's thin films, (3) the science and technology base of today's thin films needs substantial strengthening, (4) some need for alternative technologies exists, especially as the future PV marketplace expands beyond about 30 GW of annual production.
Date: April 1, 1999
Creator: Zweibel, K.
Partner: UNT Libraries Government Documents Department

Experimental study of the factors governing the Staebler-Wronski photodegradation effect in a-Si:H solar cells. Final technical report, July 7, 1994--January 15, 1998

Description: This report describes continuing studies on electroluminescence (EL), field profile, and hydrogen microstructure by the University of North Carolina, Chapel Hill, during the third year and the extension period. Based on systematic studies of the EL, the authors developed a complete model to explain the unique features of the EL as dispersive-transport-controlled, non-geminate recombinant processes. This model can explain the main features of the EL, not only in hydrogenated amorphous silicon (a-Si:H), but also in other types of trap-rich materials. By employing the forward current and EL temperature-dependence studies, information of both the localized tail states and the deep defect states in real solar-cell structures were obtained concomitantly, which is crucial for the device performance. The authors measured the internal electric field profile in p-i-n and n-i-p cells by a null-current method; they studied the structure of the hydrogen clusters in hot-wire a-Si:H films, both theoretically and experimentally, and show a clear evidence of improved structural order in hot-wire a-Si:H, which is an important factor leading to more stable materials. To link the film microstructure to the metastability, the authors also started the film stress measurements.
Date: May 1, 1998
Creator: Han, D.
Partner: UNT Libraries Government Documents Department

High Speed Data Acquisition System for Three-Dimensional X-Ray and Neutron Computed Tomography

Description: Computed tomography for nondestructive evaluation applications has been limited by system cost, resolution, and time requirements for three-dimensional data sets. FlashCT (Flat panel Amorphous Silicon High-Resolution Computed Tomography) is a system developed at Los Alamos National Laboratory to address these three problems. Developed around a flat panel amorphous silicon detector array, FlashCT is suitable for low to medium energy x-ray and neutron computed tomography at 127-micron resolution. Overall system size is small, allowing rapid transportation to a variety of radiographic sources. System control software was developed in LabVIEW for Windows NT to allow multithreading of data acquisition, data correction, and staging motor control. The system control software simplifies data collection and allows fully automated control of the data acquisition process, leading toward remote or unattended operation. The first generation of the FlashCT Data Acquisition System was completed in Au gust 1998, and since that time the system has been tested using x-ray sources ranging in energy from 60 kV to 20MV. The system has also been used to collect data for thermal neutron computed tomography at Los Alamos Neutron Science Center (LANSCE). System improvements have been proposed to provide faster data collection and greater dynamic range during data collection.
Date: July 1, 1999
Creator: Davis, A.W.; Claytor, T.N. & Sheats, M.J.
Partner: UNT Libraries Government Documents Department

Outdoor performance stability and controlled light-soak testing of amorphous silicon multijunction modules at NREL

Description: The National Renewable Energy Laboratory (NREL) has been testing amorphous silicon (a-Si) Photovoltaic (PV) modules for more than a decade. NREL has been conducting controlled light-soak testing of multifunction a-Si modules to characterize their performance for stability evaluation as well as to benchmark the technology status. Some of the test modules, after controlled light-soak testing, have been installed outdoors. The authors have observed that under outdoor exposure, the modules further degrade in performance, possibly due to lower outdoor temperatures and varying spectra. The paper presents data on the light-induced degradation for the third controlled light-soak test on multijunction a-Si modules as well as outdoor performance data on single and multijunction modules under prevailing conditions.
Date: October 1, 1995
Creator: Mrig, L.; Burdick, J.; Luft, W. & Kroposki, B.
Partner: UNT Libraries Government Documents Department

Structural Changes in a-Si:H Films Deposited on the Edge of Crystallinity

Description: Using infrared, H evolution and x-ray diffraction (XRD), the structure of high H dilution, glow discharge deposited a-Si:H films ''on the edge of crystallinity'' is examined. From the Si-H wag mode peak frequency and the XRD results, we postulate the existence of very small Si crystallites contained within the amorphous matrix, with the vast majority of the bonded H located on these crystalline surfaces. Upon annealing at ramp rates of 8-15(degree)C/min, a H evolution both of which are far below those observed for a Si:H films grown without H dilution using similar ramp rates. While the crystallite volume fraction is too small to be detected by XRD in the as-grown films, these crystallites catalyze the crystallization of the remainder of the amorphous matrix upon moderate annealing, thus explaining the existence of the low temperature H evolution peak.
Date: May 24, 1999
Creator: Mahan, A. H.; Yang, J.; Guha, S. & Williamson, D. L.
Partner: UNT Libraries Government Documents Department

Performance and Modeling of Amorphous Silicon Photovoltaics for Building-Integrated Applications (Preprint prepared for Solar 99)

Description: Amorphous silicon photovoltaic (PV) modules offer several advantages for building-integrated applications. The material can be deposited on glass or flexible substrates, which allows for products like roofing shingles and integrated PV/building glass. The material also has a uniform surface, which is ideal for many architectural applications. Amorphous silicon modules perform well in warm weather and have a small temperature coefficient for power. Depending on the building load, this may be beneficial when compared to crystalline systems. At the National Renewable Energy Laboratory, we are monitoring the performance of a triple-junction a-Si system. The system consists of 72 roofing shingles mounted directly to simulated roofing structures. This paper examines the performance of the building-integrated amorphous silicon PV system and applicability for covering residential loads. A simple model of system performance is also developed and is presented.
Date: June 7, 1998
Creator: Kroposki, B. & Hansen, R.
Partner: UNT Libraries Government Documents Department

Impact of solid-phase crystallization of amorphous silicon on the chemical structure of the buried Si/ZnO thin film solar cell interface

Description: The chemical interface structure between phosphorus-doped hydrogenated amorphous silicon and aluminum-doped zinc oxide thin films is investigated with soft x-ray emission spectroscopy (XES) before and after solid-phase crystallization (SPC) at 600C. In addition to the expected SPC-induced phase transition from amorphous to polycrystalline silicon, our XES data indicates a pronounced chemical interaction at the buried Si/ZnO interface. In particular, we find an SPC-enhanced formation of Si-O bonds and the accumulation of Zn in close proximity to the interface. For an assumed closed and homogeneous SiO2 interlayer, an effective thickness of (5+2)nm after SPC could be estimated.
Date: April 30, 2010
Creator: Bar, M.; Wimmer, M.; Wilks, R. G.; Roczen, M.; Gerlach, D.; Ruske, F. et al.
Partner: UNT Libraries Government Documents Department

Laminated Amorphous Silicon Neutron Detector (pre-print)

Description: An internal R&D project was conducted at the Special Technologies Laboratory (STL) of National Security Technologies, LLC (NSTec), to determine the feasibility of developing a multi-layer boron-10 based thermal neutron detector using the amorphous silicon (AS) technology currently employed in the manufacture of liquid crystal displays. The boron-10 neutron reaction produces an alpha that can be readily detected. A single layer detector, limited to an approximately 2-micron-thick layer of boron, has a theoretical sensitivity of about 3%; hence a thin multi-layer device with high sensitivity can theoretically be manufactured from single layer detectors. Working with National Renewable Energy Laboratory (NREL), an AS PiN diode alpha detector was developed and tested. The PiN diode was deposited on a boron-10 coated substrate. Testing confirmed that the neutron sensitivity was nearly equal to the theoretical value of 3%. However, adhesion problems with the boron-10 coating prevented successful development of a prototype detector. Future efforts will include boron deposition work and development of integrated AS signal processing circuitry.
Date: January 29, 2009
Creator: Harry McHugh, Howard Branz, Paul Stradins, and Yueqin Xu
Partner: UNT Libraries Government Documents Department