this research and development effort was designed to investigate epitaxial growth processes which will allow the use of low-cost forms of silicon for fabricating high-efficiency, cost-effective solar cells. this report covers the results of a 1-y effort which involved characterization of potentially low-cost silicon substrates, epitaxial growth studies, and the fabrication and evaluation of solar cells made in the epitaxial layers. silicon substrates prepared from metallurgical grade silicon by potentially low-cost purification and growth techniques form satisfactory substrates for epitaxial growth and the fabrication of 10 to 12 efficient solar cells. the allowable range of variation in the key parameters of the epitaxial process and cell structures was determined and it was found that a greater variation in these parameters is possible for solar cells compared with those required for epitaxial devices now produced in the semiconductor industry. thin-film epitaxially grown solar cells were reproducibly demonstrated with efficiencies of over 10. a scale-up to practical sized cells was shown to be feasible by fabricating cells of 10-cm exp 2 area with almost 10 efficiency. (era citation 81:025263)