Lanterna Rally

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Published: 1980

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The overall objective of this program is to define the effects of impurities, various thermochemical processes, and any impurity-process interactions upon the performance of terrestrial solar cells. The results of the study form a basis for silicon producers, wafer manufacturers, and cell fabricators to develop appropriate cost-benefit relationships for the use of less pure, less costly solar grade silicon. Fifteen 4 ohm-cm p-type ingots were grown during this quarter, both single crystal and polycrystal, to initiate the Phase IV effort. These ingots were evaluated through electrical measurements, spark source mass spectroscopy, and atomic absorption spectroscopy of the melt. Carbon and oxygen concentrations were measured by ir spectroscopy and found to be within normal limits. Cells made from Mo-doped poly material exhibited very low efficiencies. Cells made from vanadium-contaminated polycrystalline Si also showed very low efficiency due to junction shorting effects; however, a few of the cels with lower inclusion densities could be measured. Projections of effective lfe of solar cells containing some specific impurities were made. On the basis of data derived from elevated temperature stressing of solar cell material, it is concluded that cells containing Mo or Ti as impurities will not degrade appreciably during a twenty year period due to impurity aging effects. However, initial data indicate that cells containing Cr, Nb, or Ag degrade more rapidly than Mo or Ti-doped cells, and may not retain useful efficiencies over a twenty year period. (WHK).