The work performed during the first quarter included the development of epitaxial baseline solar cell structures grown on conventional single crystal substrates and initial studies of epitaxial growth and the fabrication of solar cells on one type of polycrystalline substrate (Wacker SILSO). Details of the growth and fabrication procedures for the baseline solar cells are given along with measured cell parameters. The results show that solar cells fabricated on epitaxial layers of about one mil thickness can produce AM-1 efficiency of 12%. Reproducibility of these results was established and the direction to be taken for higher efficiency is identified. Growth studies on polycrystalline substrates were started and x-ray topographic studies of the epitaxial layers showed encouraging results in that a substantially lower defect density was noted in the grown layer. Initial results on epitaxial solar cells fabricated on polycrystalline substrates are discussed along with some limitations associated with the use of this material.

The epitaxial growth of thin solar-cell structures was extended to include another potentially low-cost form of silicon: upgraded metallurgical grade silicon obtained from Dow Corning. An AM-1 efficiency of 12.4% was achieved with a cell structure having only 14 .mu.m of silicon grown on the Dow Corning. The best efficiency obtained was 13% on a 50-.mu.m thick structure. It was found that titanium (2 x 10/sup 14/ A/cm/sup -3/ level) intentionally incorporated into the substrates primarily causes a reduction in the short-circuit current for both epitaxial and bulk cells. However, the epitaxial cells were much less effected by the presence of titanium and efficiencies as high as 11.7% were obtained while the efficiency for bulk cells was approx. 8%. Preliminary experiments in a laboratory model of RCA's advanced rotary disc reactor have produced solar cells with 10 to 12% efficiency. These cells were grown on single-crystal control substrates and the growth which included studies of submicron surface layers showed a trend toward increased short-circuit current density for shallower junctions.