Low-cost silicon substrates by directional solidification. Final report

Technical Report · Wed Dec 01 04:00:00 EST 1982

DOI:https://doi.org/10.2172/6772267· OSTI ID:6772267

Schmid, F.; Khattak, C. P.

A one-year effort was carried out to evaluate the use of directional solidification of commercially available metallurgical grade (MG) silicon by the Heat Exchanger Method (HEM) to produce substrates suitable for solar cell fabrication. Metallurgical grade (MG) silicons from numerous sources world-wide were evaluated and it was found that the impurity content varied depending upon the purity of the raw material, mix used in the arc furnace, processing and handling techniques used in the MG silicon plant. In all cases very effective segregation of impurities was seen and single crystal structure was achieved in ingots after directional solidification by HEM; the amount of single crystal material varied with the source of meltstock and processing parameters in the furnace. The HEM furnace was used to melt and hold the material for in situ refinement prior to directional solidification. The effect of vacuum, slagging, stirring of the melt, moist argon blowing through the melt and double solidification were studied on the refinement of MG silicon. The sensitivity of these processing techniques was evaluated as a function of time and temperature in some cases. The moist argon blowing and double solidification were found to be the most effective processing techniques to reduce impurities. It is possible to combine slagging and moist argon blowing to achieve more effective purification. It was shown that 7.2% efficient diffused solar cells and 11.84% epitaxial cells can be fabricated from HEM solidified material using commercially available MG silicon. Shunting of cells was observed in the area of SiC particles and this is attributed to the high carbon content of the MG silicon. The most serious limitation of using this approach is therefore the carbon content of the MG meltstock. MG silicon from India and South Africa were found to be the best sources of MG silicon for this approach.

• Research Organization: Crystal Systems, Inc., Salem, MA (USA)
• DOE Contract Number: AC02-77CH00178
• OSTI ID: 6772267
• Report Number(s): SERI/TR-9171-1-T2; ON: DE84011552
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
36 MATERIALS SCIENCE
360601 -- Other Materials-- Preparation & Manufacture
AFRICA
ASIA
CRYSTAL GROWTH
CRYSTAL GROWTH METHODS
DEVELOPING COUNTRIES
DIFFUSION
EFFICIENCY
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
EPITAXY
HEAT EXCHANGER METHOD
IMPURITIES
INDIA
PHYSICAL PROPERTIES
SEMIMETALS
SILICON
SOUTH AFRICA