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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

High-efficiency solar cells using HEM silicon

Description: Developments in Heat Exchanger Method (HEM) technology for production of multicrystalline silicon ingot production have led to growth of larger ingots (55 cm square cross section) with lower costs and reliability in production. A single reusable crucible has been used to produce 18 multicrystalline 33 cm square cross section 40 kg ingots, and capability to produce 44 cm ingots has been demonstrated. Large area solar cells of 16.3% (42 cm{sup 2}) and 15.3% (100 cm{sup 2}) efficiency have been produced without optimization of the material production and the solar cell processing.
Date: December 31, 1994
Creator: Khattak, C.P.; Schmid, F. & Schubert, W.K.
Partner: UNT Libraries Government Documents Department

New Opportunities in Crystalline Silicon R&D

Description: To support the expected growth of the silicon solar cell industry, we believe that research and development (R&D) activities should be carried out in the following areas: polysilicon feedstock for the PV industry; thin-layer silicon deposition methods, and more environmentally benign cell and module manufacturing processes. For each of these activities, we identify the main issues that needed to be addressed.
Date: October 6, 1998
Creator: Tsuo, Y. S.; Wang, T. H.; Ciszek, T. F. (National Renewable Energy Laboratory) & Menna, P. (ENEA, Portici, Italy)
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

University Crystalline Silicon Photovoltaics Research and Development

Description: The overall goal of the program is to advance the current state of crystalline silicon solar cell technology to make photovoltaics more competitive with conventional energy sources. This program emphasizes fundamental and applied research that results in low-cost, high-efficiency cells on commercial silicon substrates with strong involvement of the PV industry, and support a very strong photovoltaics education program in the US based on classroom education and hands-on training in the laboratory.
Date: August 18, 2008
Creator: Rohatgi, Ajeet; Yelundur, Vijay; Ebong, Abasifreke & Kim, Dong Seop
Partner: UNT Libraries Government Documents Department

Reactive Ion Etching for Randomly Distributed Texturing of Multicrystalline Silicon Solar Cells

Description: The quality of low-cost multicrystalline silicon (mc-Si) has improved to the point that it forms approximately 50% of the worldwide photovoltaic (PV) power production. The performance of commercial mc-Si solar cells still lags behind c-Si due in part to the inability to texture it effectively and inexpensively. Surface texturing of mc-Si has been an active field of research. Several techniques including anodic etching [1], wet acidic etching [2], lithographic patterning [3], and mechanical texturing [4] have been investigated with varying degrees of success. To date, a cost-effective technique has not emerged.
Date: May 1, 2002
Creator: ZAIDI, SALEEM H
Partner: UNT Libraries Government Documents Department

Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Semiannual technical report, 1 January 1996--30 June 1996

Description: Two specific objectives of Solarex`s program are to reduce the manufacturing cost for polycrystalline silicon photovoltaic modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three. This report highlights accomplishments during the period of January 1 through June 30, 1996. Accomplishments include: began the conversion of production casting stations to increase ingot size; operated the wire saw in a production mode with higher yields and lower costs than achieved on the ID saws; developed and qualified a new wire guide coating material that doubles the wire guide lifetime and produces significantly less scatter in wafer thickness; completed a third pilot run of the cost-effective Al paste back-surface-field (BSF) process, verifying a 5% increase in cell efficiency and demonstrating the ability to process and handle the BSF paste cells; completed environmental qualification of modules using cells produced by an all-print metallization process; optimized the design of the 15.2-cm by 15.2-cm polycrystalline silicon solar cells; demonstrated the application of a high-efficiency process in making 15.2-cm by 15.2-cm solar cells; demonstrated that cell efficiency increases with decreasing wafer thickness for the Al paste BSF cells; qualified a vendor-supplied Tedlar/ethylene vinyl acetate (EVA) laminate to replace the combination of separate sheets of EVA and Tedlar backsheet; demonstrated the operation of a prototype unit to trim/lead attach/test modules; and demonstrated the operation of a wafer pull-down system for cassetting wet wafers.
Date: January 1, 1997
Creator: Wohlgemuth, J.
Partner: UNT Libraries Government Documents Department

Light-trapped, interconnected, silicon-film {trademark} modules. Annual subcontract report, 18 November 1994--18 November 1995

Description: This report describes the first year of work performed by AstroPower, Inc., of Newark, Delaware, under the Thin-Film PV Partnership Program. The work led to the development of a new barrier-coated substrate that has enabled high-quality thin-layer polycrystalline silicon to be grown on a low-cost substrate. High diffusion lengths were measured after external phosphorous gettering. This led to a confirmed efficiency for a 0.57cm{sup 2}, thin-layer solar cell grown on a low-cost substrate.
Date: March 1, 1996
Creator: Hall, R.B.; Rand, J.A.; Cotter, J.E. & Ford, D.H.
Partner: UNT Libraries Government Documents Department

Photovoltaic manufacturing technology monolithic amorphous silicon modules on continuous polymer substrates. Annual technical progress report, 5 July 1995--4 June 1996

Description: Iowa Thin Film Technologies` goal is to develop the most cost-effective photovoltaic manufacturing process possible. During the first year, they developed the capability of sputtering a high-quality (Zn(Al)O) successfully implemented increased deposition rates for the ZnO top contact deposition; improved registration and ink-line width to reduce area loss due to interconnects; developed a new alignment process and sensor to improve the speed and accuracy of registration for the patterning processes; developed a new Silver ink composition that allows finer print lines and lower series resistance; demonstrated an 8% overall improvement in area utilization; evaluated water-based insulator inks for compatibility with their processes; investigated and tested the use of roll-based lamination as a means to reduce the cost of assembly; developed straight roll lamination capability using pressure-sensitive adhesives and thermally activated bonding; and evaluated the use of the standard EVA/Tefzel encapsulant with a roll laminator.
Date: February 1, 1997
Creator: Jeffrey, F.
Partner: UNT Libraries Government Documents Department

Plasma etching, texturing, and passivation of silicon solar cells

Description: The authors improved a self-aligned emitter etchback technique that requires only a single emitter diffusion and no alignments to form self-aligned, patterned-emitter profiles. Standard commercial screen-printed gridlines mask a plasma-etchback of the emitter. A subsequent PECVD-nitride deposition provides good surface and bulk passivation and an antireflection coating. The authors used full-size multicrystalline silicon (mc-Si) cells processed in a commercial production line and performed a statistically designed multiparameter experiment to optimize the use of a hydrogenation treatment to increase performance. They obtained an improvement of almost a full percentage point in cell efficiency when the self-aligned emitter etchback was combined with an optimized 3-step PECVD-nitride surface passivation and hydrogenation treatment. They also investigated the inclusion of a plasma-etching process that results in a low-reflectance, textured surface on multicrystalline silicon cells. Preliminary results indicate reflectance can be significantly reduced without etching away the emitter diffusion.
Date: November 1, 1998
Creator: Ruby, D.S.; Yang, P.; Zaidi, S.; Brueck, S.; Roy, M. & Narayanan, S.
Partner: UNT Libraries Government Documents Department

Large-area Silicon-Film{trademark} panels and solar cells

Description: This report describes AstroPower`s success in improving its material and processing capabilities during the first phase of this 3-year contract through the Photovoltaic Manufacturing Technology (PVMaT) program. Key results include the demonstration of a 14.6%-efficient Silicon-Film{trademark} solar cell. This laboratory result (1.0 cm{sup 2}) provides the direction needed to develop and optimize continuous, in-line production processes. The continuous nature of the Silicon-Film{trademark} sheet fabrication process is being extended into the solar-cell processing sequence. Plans are in place to make the wafer cleaning, gettering, and diffusion steps all continuous during the scope of this program.
Date: January 1997
Creator: Rand, J. A.; Barnett, A. M. & Checchi, J. C.
Partner: UNT Libraries Government Documents Department

Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Annual subcontract report, 1 January 1996--31 December 1996

Description: This report describes Solarex`s accomplishments during this phase of the Photovoltaic Manufacturing Technology (PVMaT) program. During this reporting period, Solarex researchers converted 79% of production casting stations to increase ingot size and operated them at equivalent yields and cell efficiencies; doubled the casting capacity at 20% the cost of buying new equipment to achieve the same capacity increase; operated the wire saws in a production mode with higher yields and lower costs than achieved on the ID saws; purchased additional wire saws; developed and qualified a new wire-guide coating material that doubles the wire-guide lifetime and produces significantly less scatter in wafer thickness; ran an Al paste back-surface-field process on 25% of all cells in manufacturing; completed environmental qualification of modules using cells produced by an all-print metallization process; qualified a vendor-supplied Tedlar/ethylene vinyl acetate (EVA) laminate to replace the combination of separate sheets of EVA and Tedlar backsheet; substituted RTV adhesive for the 3M Very High Bond tape after several field problems with the tape; demonstrated the operation of a prototype unit to trim/lead attach/test modules; demonstrated the use of light soldering for solar cells; demonstrated the operation of a wafer pull-down system for cassetting wet wafers; and presented three PVMaT-related papers at the 25th IEEE Photovoltaic Specialists Conference.
Date: October 1, 1997
Creator: Wohlgemuth, J.
Partner: UNT Libraries Government Documents Department

Sixth workshop on the role of impurities and defects in silicon device processing

Description: The Sixth Workshop on the Role of Impurities and Defects in Silicon Device Processing was held in Snowmass Village, August 12-14, 1996. The workshop was attended by 87 participants from academic institutions and photovoltaic industry representatives, from the United States, Australia, Belgium, Canada, France, Germany, Italy, Japan, Belgium, and The Netherlands. The workshop consisted of nine sessions that addressed different aspects of impurities and defects in silicon and applications to solar-cell processing. Each session opened with some review talks summarizing recent advances in this field and introduced important issues for further discussions during a subsequent panel discussion session. In addition, the latest research results were presented in two poster sessions.
Date: September 1, 1996
Creator: Tan, T.; Swanson, R. & Sopori, B.
Partner: UNT Libraries Government Documents Department

High-efficiency cell structures and processes applied to photovoltaic-grade Czochralski silicon

Description: The authors performed a detailed study to examine the limiting performance available using photovoltaic-grade Cz silicon. Photovoltaic-grade silicon refers to silicon produced by the photovoltaic industry, which may differ from the silicon used in the semiconductor device industry in impurity and defect concentrations.The study included optimization of fabrication processes, development of advanced device structures, and detailed model calculations to project future performance improvements. Process and device optimization resulted in demonstration of 75-{micro}s bulk lifetimes and 17.6%-efficient large-area cells using photovoltaic-grade Cz silicon. Detailed calculations based on the material and device evaluation of the present work project efficiencies of 20% for photovoltaic-grade Cz silicon with properly optimized processing and device structures.
Date: December 1, 1996
Creator: Gee, J.M.; King, R.R. & Mitchell, K.W.
Partner: UNT Libraries Government Documents Department

Large-area Silicon-Film{trademark} panels and solar cells. Phase 2 technical report, January 1996--December 1996

Description: The Silicon-Film{trademark} process is on an accelerated path to large-scale manufacturing. A key element in that development is optimizing the specific geometry of both the Silicon-Film{trademark} sheet and the resulting solar cell. That decision has been influenced by cost factors, engineering concerns, and marketing issues. The geometry investigation has focused first on sheet nominally 15 cm wide. This sheet generated solar cells with areas of 240 cm{sup 2} and 675 cm{sup 2}. Most recently, a new sheet fabrication machine was constructed that produces Silicon-Film{trademark} with a width in excess of 30 cm. Test results have indicated that there is no limit to the width of sheet generated by this process. The new wide material has led to prototype solar cells with areas of 300, 400, and 1,800 cm{sup 2}. Significant advances in solar-cell processing have been developed in support of fabricating large-area devices, including uniform emitter diffusion and anti-reflection coatings.
Date: March 1, 1997
Creator: Rand, J.A.; Barnett, A.M.; Checchi, J.C.; Culik, J.S.; Collins, S.R.; Ford, D.H. et al.
Partner: UNT Libraries Government Documents Department

Advanced Silicon Space Solar Cells Using Nanotechnology

Description: Application of nanotechnology and advanced optical structures offer new possibilities for improved radiation tolerance in silicon solar cells. We describe the application of subwavelength diffractive structures to enhance optical absorption near the surface, and thereby improve the radiation tolerance.
Date: March 31, 1999
Creator: Gee, J.M.; Ruby, D.S. & Zaidi, S.H.
Partner: UNT Libraries Government Documents Department

Amorphous silicon research. Phase III technical progress report, August 1, 1996--July 31, 1997

Description: The principal objective of this R&D program is to expand, enhance and accelerate knowledge and capabilities for the development of high-performance, two-terminal multijunction hydrogenated amorphous silicon (a-Si) alloy cells and modules. The near-term goal of the program is to achieve 12% stable active-area efficiency using the multijunction approach. The long-term goal is to achieve 15% stable efficiency multijunction modules. The major effort of this program is to develop high efficiency component cells and incorporate them in the triple-junction structure to obtain the highest stable efficiency. New and improved deposition regimes were investigated to obtain better cell performance. Fundamental studies to obtain better understanding of material and cell performance were undertaken.
Date: November 1, 1997
Creator: Guha, S.
Partner: UNT Libraries Government Documents Department

Recent progress on the self-aligned, selective-emitter silicon solar cell

Description: We developed a self-aligned emitter etchback technique that requires only a single emitter diffusion and no alignments to form self-aligned, patterned-emitter profiles. Standard commercial, screen-printed gridlines mask a plasma-etchback of the emitter. A subsequent PECVD-nitride deposition provides good surface and bulk passivation and an antireflection coating. We succeeded in finding a set of parameters which resulted in good emitter uniformity and improved cell performance. We used full-size multicrystalline silicon (mc-Si) cells processed in a commercial production line and performed a statistically designed, multiparameter experiment to optimize the use of a hydrogenation treatment to increase performance. Our initial results found a statistically significant improvement of half an absolute percentage point in cell efficiency when the self-aligned emitter etchback was combined with a 3-step PECVD-nitride surface passivation and hydrogenation treatment. 12 refs., 4 figs., 3 tabs.
Date: October 1, 1997
Creator: Ruby, D.S.; Yang, P. & Roy, M.
Partner: UNT Libraries Government Documents Department

High-efficiency one-sun photovoltaic module demonstration using solar-grade CZ silicon. Final report

Description: This work was performed jointly by Sandia National Laboratories (Albuquerque, NM) and Siemens Solar Industries (Camarillo, CA) under a Cooperative Research and Development Agreement (CRADA 1248). The work covers the period May 1994 to March 1996. The purpose of the work was to explore the performance potential of commercial, photovoltaic-grade Czochralski (Cz) silicon, and to demonstrate this potential through fabrication of high-efficiency cells and a module. Fabrication of the module was omitted in order to pursue further development of advanced device structures. The work included investigation of response of the material to various fabrication processes, development of advanced cell structures using the commercial material, and investigation of the stability of Cz silicon solar cells. Some important achievements of this work include the following: post-diffusion oxidations were found to be a possible source of material contamination; bulk lifetimes around 75 pts were achieved; efficiencies of 17.6% and 15.7% were achieved for large-area cells using advanced cell structures (back-surface fields and emitter wrap-through); and preliminary investigations into photodegradation in Cz silicon solar cells found that oxygen thermal donors might be involved. Efficiencies around 20% should be possible with commercial, photovoltaic-grade silicon using properly optimized processes and device structures.
Date: October 1, 1996
Creator: Gee, J. M.
Partner: UNT Libraries Government Documents Department

Light-trapped, interconnected, Silicon-Film{trademark} modules. Final technical status report

Description: AstroPower has continued its development of an advanced thin-silicon-based photovoltaic module product. This module combines the performance advantages of thin light-trapped silicon layers with the capability of integration into a low-cost, monolithically interconnected module. This report summarized work carried out over a 3-year, cost-shared contract. Key results accomplished during this phase include an NREL-verified conversion efficiency of 12.5% on a 0.47-cm{sup 2} device. The device structure used an insulating substrate and an active layer less than 100 {micro}m thick. A new metalization scheme was designed using insulating crossovers. This technology was demonstrated on a 36-segment, 321-cm{sup 2}, interconnected module. That module was tested at NREL with an efficiency of 9.79%. Further advances in metalization have led to an advanced single back-contact design that will offer low cost through ease of processing and higher performance through reduced shading.
Date: April 1, 1998
Creator: Hall, R.B.; Rand, J.A.; Ford, D.H. & Ingram, A.E.
Partner: UNT Libraries Government Documents Department

Fundamental understanding and development of low-cost, high-efficiency silicon solar cells

Description: The overall objectives of this program are (1) to develop rapid and low-cost processes for manufacturing that can improve yield, throughput, and performance of silicon photovoltaic devices, (2) to design and fabricate high-efficiency solar cells on promising low-cost materials, and (3) to improve the fundamental understanding of advanced photovoltaic devices. Several rapid and potentially low-cost technologies are described in this report that were developed and applied toward the fabrication of high-efficiency silicon solar cells.
Date: May 1, 2000
Creator: ROHATGI,A.; NARASIMHA,S.; MOSCHER,J.; EBONG,A.; KAMRA,S.; KRYGOWSKI,T. et al.
Partner: UNT Libraries Government Documents Department

Fundamental Understanding and Development of Low-Cost, High-Efficient Silicon Solar Cells Final Progress Report: Sept. 1999 - June 2000

Description: The overall objectives of this program are to (1) develop rapid and low-cost processes for manufacturing that can improve yield, throughput, and performance of silicon photovoltaic devices, (2) design and fabricate high-efficiency solar cells on promising low-cost materials, and (3) improve the fundamental understanding of advanced photovoltaic devices. Several rapid and potentially low-cost technologies are described in this report that were developed and applied toward the fabrication of high-efficiency silicon solar cells.
Date: February 1, 2001
Creator: ROHATGI, A.; EBNG, A.; YELUNDUR, V.; HILALI, M.; JEONG, J.; PREGELJ, A. et al.
Partner: UNT Libraries Government Documents Department