Engineering topics

Dosaj, V. D.

Publications and source records attributed to Dosaj, V. D..

7 records

NASA NTRS1979

Solar silicon via the Dow Corning process

Technical feasibility for high volume production of solar cell-grade silicon is investigated. The process consists of producing silicon from pure raw materials via the carbothermic reduction of quartz. This silicon was then purified to solar grade by impurity segregation during Czochralski crystal growth. Commercially available raw materials were used to produce 100 kg quantities of silicon during 60 hour periods in a direct arc reactor. This silicon produced single crystalline ingot, during a second Czochralski pull, that was fabricated into solar cells having efficiencies ranging from 8.2 percent to greater than 14 percent. An energy analysis of the entire process indicated a 5 month payback time.

Hunt, L. P.↗

NASA NTRS1979

Progress on the Dow Corning process for solar-grade silicon

The Dow Corning approach to increasing the resistivity of solar-grade silicon from about 0.04 ohm-cm (40 ppma B) to greater than 0.1 ohm-cm (10 ppma B) involves the use of high-purity raw materials carbothermically reduced in a specially designed electric arc furnace. Final purification occurs during Czochralski crystal growth of a polycrystalline ingot. This small-scale purification technology has resulted in silicon that has been fabricated into solar cells with a maximum AM1 conversion efficiency of 13.4%.

Hunt, L. P.↗

NASA NTRS1978

High-purity silicon for solar cell applications

The article discusses the production of solar cells from high-purity silicon. The process consists of reducing the level of impurities in the raw materials, preventing material contamination before and after entering the furnace, and performing orders-of-magnitude reduction of metal impurity concentrations. The high-purity raw materials are considered with reference to carbon reductants, silica, and graphite electrodes. Attention is also given to smelting experiments used to demonstrate, in an experimental-scale furnace, the production of high-purity SoG-Si. It is found that high-purity silicon may be produced from high-purity quartz and chemically purified charcoal in a 50-kVA arc furnace. The major contamination source is shown to be impurities from the carbon reducing materials.

Dosaj, V. D.↗

NASA NTRS1978

Solar silicon via the Dow Corning process

Carbon, as a reductant for quartz, must be made available so as to have suitable reactivity in conjunction with high purity, especially with respect to boron and phosphorus. A detailed experimental plan was developed to do this. Different sources of carbon were selected to be subjected to various purification methods and reactivity-enhancement processes. A developmental scale arc furnace was installed to perform quartz-carbon reactivity testing.

Hunt, L. P.↗

NASA NTRS1978

Advances in the Dow Corning process for solar-grade silicon

The Dow Corning process consists of the carbothermic reduction of silica to produce silicon that is then purified by unidirectional solidification. The process has produced silicon of semiconductor quality with respect to all elements except boron and phosphorus at about 10 ppma and aluminum at 0.1 ppma. Solar cells produced from this silicon gave AM0 conversion efficiencies of 11%. A process cost analysis is presented.

Hunt, L. P.↗

NASA NTRS1977

Solar silicon via improved and expanded metallurgical silicon technology

A completed preliminary survey of silica sources indicates that sufficient quantities of high-purity quartz are available in the U.S. and Canada to meet goals. Supply can easily meet demand for this little-sought commodity. Charcoal, as a reductant for silica, can be purified to a sufficient level by high-temperature fluorocarbon treatment and vacuum processing. High-temperature treatment causes partial graphitization which can lead to difficulty in smelting. Smelting of Arkansas quartz and purified charcoal produced kilogram quantities of silicon having impurity levels generally much lower than in MG-Si. Half of the goal was met of increasing the boron resistivity from 0.03 ohm-cm in metallurgical silicon to 0.3 ohm-cm in solar silicon. A cost analysis of the solidification process indicate $3.50-7.25/kg Si for the Czochralski-type process and $1.50-4.25/kg Si for the Bridgman-type technique.

Hunt, L. P.↗

NASA NTRS1976

Production of solar-grade silicon from purified metallurgical silicon

The long-term goal of this work is to produce silicon of solar-grade quality at 3 x 10 to the 6th kg/y for less than $10/kg by, or before 1986. The approach is to improve and expand upon the technology used today to commercially produce metallurgical-grade silicon (MG-Si). This is currently being accomplished by using purer raw materials in the arc furnace process for producing MG-Si, by upgrading the furnace itself, and by unidirectionally solidifying the molten silicon exiting the furnace. Solar cells fabricated from partially purified MG-Si have shown average AM0 efficiencies in the range of 9-11%. Since further MG-Si purification yet remains possible, fabrication of cells of considerably higher conversion efficiency is deemed feasible.

Hunt, L. P.↗