Epitaxial silicon solar cells

Epitaxial silicon solar cell structures have been grown on both single crystal, as well as polycrystalline EFG "ribbon" substrates. Using EFG substrates, a comparison is made of the material, and electrical characteristics of solar cells fabricated from grown epitaxial junctions and those formed by direct diffusion into the ribbon. Efficiencies of 10% (AM-1) have been achieved with the epitaxial structures, which are substantially higher than achieved by diffusion. The improvement is shown to result mainly from the lower saturation current density of the epitaxial junctions. Epitaxial single crystal P⁺/P/N/N⁺solar cell structures containing intentionally graded N-base regions were also studied. Near ideal I-V characteristics were obtained with an open circuit voltage of 636 mv, fill factor of 0.79 and AM-1 efficiency of 12.6%.