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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth is investigated. An existing RTR apparatus is to be upgraded to its full capabilities and operated routinely to investigate and optimize the effects of various growth parameters on growth results. A new RTR apparatus was constructed to incorporate increased capabilities and improvements over the first apparatus and to be capable of continuous growth. New high power lasers were implemented and this led to major improvements in growth velocity -- 4 inch/min. growth has been demonstrated. A major step in demonstration of the full feasibility of the RTR process is reported in the demonstration of RTR growth from CVD polyribbon rather than sliced polyribbon ingots. Average solar cell efficiencies of greater than 9% and a best cell efficiency of 11.7% are reported. Processing was shown to provide a substantial improvement in material minority carrier diffusion length. An economic analysis is reported which treats both the polyribbon fabrication and RTR processes.

Gurtler, R. W.↗
NASA NTRS1978

Development of advanced methods for continuous Czochralski growth. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

The three components required to modify the furnace for batch and continuous recharging with granular silicon were designed. The feasibility of extended growth cycles up to 40 hours long was demonstrated by a recharge simulation experiment; a 6 inch diameter crystal was pulled from a 20 kg charge, remelted, and pulled again for a total of four growth cycles, 59-1/8 inch of body length, and approximately 65 kg of calculated mass.

Wolfson, R. G.↗
NASA NTRS1977

Heat exchanger-ingot casting/slicing process, phase 1: Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

A controlled growth, heat-flow and cool-down process is described that yielded silicon with a high degree of single crystallinity. Even when the seed melted out, very large grains formed. Solar cell samples made from cast material yielded conversion efficiency of over 9%. Representative characterizations of grown silicon demonstrated a dislocation density of less than 100/sq cm and a minority carrier diffusion length of 31 micron. The source of silicon carbide in silicon ingots was identified to be from graphite retainers in contact with silica crucibles. Higher growth rates were achieved with the use of a graphite plug at the bottom of the silica crucible.

Schmid, F.↗
NASA NTRS1978

Delayed fracture of silicon: Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

Bar specimens were cut from ingots of single crystal silicon, and acid etched prior to testing. Artificial surface flaws were introduced in specimens by indentation with a Knoop hardness tester. The specimens were loaded in four-point bending to 95 percent of the nominal fracture stress, while keeping the surface area, containing the flaw, wet with test liquids. No evidence of delayed fracture, and, therefore stress corrosion, of single crystal silicon was observed for liquid environments including water, acetone, and aqueous solutions of NaCl, NH4OH, and HNO3, when tested with a flaw parallel to a (110) surface. The fracture toughness was calculated.

Chen, T. J.↗
NASA NTRS1978

Silicon Sheet Growth Development for the Large Area Sheet Task of the Low Cost Solar Array Project. Heat Exchanger Method - Ingot Casting Fixed Abrasive Method - Multi-Wire Slicing

Solar cells fabricated from HEM cast silicon yielded up to 15% conversion efficiencies. This was achieved in spite of using unpurified graphite parts in the HEM furnace and without optimization of material or cell processing parameters. Molybdenum retainers prevented SiC formation and reduced carbon content by 50%. The oxygen content of vacuum cast HEM silicon is lower than typical Czochralski grown silicon. Impregnation of 45 micrometers diamonds into 7.5 micrometers copper sheath showed distortion of the copper layer. However, 12.5 micrometers and 15 micrometers copper sheath can be impregnated with 45 micrometers diamonds to a high concentration. Electroless nickel plating of wires impregnated only in the cutting edge showed nickel concentration around the diamonds. This has the possibility of reducing kerf. The high speed slicer fabricated can achieve higher speed and longer stroke with vibration isolation.

Schmid, F.↗
NASA NTRS1978

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area sheet task of the low-cost solar array project

A new calculation of the effects of thermal stresses during growth on silicon ribbon quality is reported. Thermal stress distributions are computed for ribbon growth under a variety of temperature profiles. A growth rate of 55 cu cm/min with a single ribbon was achieved. The growth of RTR ribbon with a fairly uniform parallel dendritic structure was demonstrated. Results with two approaches were obtained for reducing the Mo impurity level in polycrystalline feedstock. Coating the Mo substrate with Si3N4 does not effect thermal shear separation of the polyribbon; this process shows promise of improving cell efficiency and also increasing the useful life of the molybdenum substrate. A number of solar cells were fabricated on RTR silicon grown from CVD feedstock.

Baghdadi, A.↗
NASA NTRS1978

Continuous Czochralski growth: Silicon sheet growth development of the large area silicon sheet task of the Low Cost Silicon Solar Array project

The primary objective of this contract is to develop equipment and methods for the economic production of single crystal ingot material by the continuous Czochralski (CZ) process. Continuous CZ is defined for the purpose of this work as the growth of at least 100 kilograms of ingot from only one melt container. During the reporting period (October, 1977 - September, 1978), a modified grower was made fully functional and several recharge runs were performed. The largest run lasted 44 hours and over 42 kg of ingot was produced. Little, if any, degradation in efficiency was observed as a result of pulling multiple crystals from one crucible. Solar efficiencies observed were between 9.3 and 10.4% AMO (13.0 and 14.6% AMI) compared to 10.5% (14.7% AMI) for optimum CZ material control samples. Using the SAMICS/IPEG format, economic analysis of continuous CZ suggests that 1986 DoE cost goals can only be met by the growth of large diameter, large mass crystals.

Source record↗
NASA NTRS1978

Continuous Czochralski Growth. Silicon Sheet Growth Development of the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

The JPL Continuous Czochralski Growth Facility is now essentially complete and is functional. In this reporting period, a silicon lump recharging device was designed, and a prototype was built which performed well in simulated recharge tests. The large chamber (designed to accommodate a 14-inch hot zone) was put into operation initially with the standard hot zone in order to compare performance with previous experience. Some modifications were made to the hot zones in the larger chamber due to considerably larger radiative heat losses. Several short (one-ingot) runs were performed and four continuous runs were attempted. The largest continuous run lasted 64 hours and produced 57 kilograms of ingot.

Merz, F.↗
NASA NTRS1979

Silicon-on-ceramic Process: Silicon Sheet Growth and Device Development for the Large-area Silicon Sheet and Cell Development Tasks of the Low-cost Solar Array Project

Significant progress is reported in fabricating a 4 sq cm cell having a 10.1 percent conversion efficiency and a 10 sq cm cell having a 9.2 percent conversion efficiency. The continuous (SCIM) coater succeeded in producing a 16 sq cm coating exhibiting unidirectional solidification and large grain size. A layer was grown at 0.2 cm/sec in the experimental coater which was partially dendritic but also contained a large smooth area approximately 100 micron m thick. The dark characteristic measurements of a typical SCC solar cell yield shunt resistance values of 10K ohms and series resistance values and 0.4 ohm. The production dip-coater is operating at over 50 percent yield in terms of good cell quality material. The most recent run yielded 13 good substrates out of 15.

Chapman, P. W.↗
NASA NTRS1979

Laser-zone Growth in a Ribbon-to-ribbon (RTR) Process Silicon Sheet Growth Development for the Large Area Silicon Sheet Task of the Low Cost Solar Array Project

A technique for growing limited-length ribbons continually was demonstrated. This Rigid Edge technique can be used to recrystallize about 95% of the polyribbon feedstock. A major advantage of this method is that only a single, constant length silicon ribbon is handled throughout the entire process sequence; this may be accomplished using cassettes similar to those presently in use for processing Czochralski waters. Thus a transition from Cz to ribbon technology can be smoothly affected. The maximum size being considered, 3 inches x 24 inches, is half a square foot, and will generate 6 watts for 12% efficiency at 1 sun. Silicon dioxide has been demonstrated as an effective, practical diffusion barrier for use during the polyribbon formation.

Baghdadi, A.↗
NASA NTRS1979

Continuous Czochralski Growth. Silicon Sheet Growth Development of the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

During the reporting period, a successful 100 kilogram run was performed. Six ingots of 13 cm diameter were grown, ranging in size from 15.5 kg to 17.7 kg. Melt replenishment methods included both poly rod and lump feed material. Samples from each ingot were prepared for solar cell fabrication and analyses, impurity analysis, and structural studies. The furnace was converted to the 14-inch hot zone and preliminary heat runs were performed. Two sucessful runs were demonstrated, by growing 25 kg ingots from 30 kg melts. Also, a 100 kg run was attempted, utilizing the 14 inch crucible hot zone, but was prematurely terminated due to excessive monoxide which accumulated on the viewports and a seed failure.

Merz, F.↗
NASA NTRS1979

Silicon Ingot Casting - Heat Exchanger Method Multi-wire Slicing - Fixed Abrasive Slicing Technique. Phase 3 Silicon Sheet Growth Development for the Large Area Sheet Task of the Low-cost Solar Array Project

Several 20 cm diameter silicon ingots, up to 6.3 kg. were cast with good crystallinity. The graphite heat zone can be purified by heating it to high temperatures in vacuum. This is important in reducing costs and purification of large parts. Electroplated wires with 45 um synthetic diamonds and 30 um natural diamonds showed good cutting efficiency and lifetime. During slicing of a 10 cm x 10 cm workpiece, jerky motion occurred in the feed and rocking mechanisms. This problem is corrected and modifications were made to reduce the weight of the bladeheat by 50%.

Schmid, F.↗