Efficiency (>15%) for thin-film epitaxial silicon solar cells on 70 cm2 area off spec silicon substrate using porous silicon segmented mirrors

We report on the beneficial use of embedded segmented porous silicon broad-band optical reflectors for thin-film epitaxial silicon solar cells. These reflectors are formed by gradual increase of the spatial period between the layer segments, allowing for an enhanced absorption of low energy photons in the epitaxial layer. By combining these reflectors with wellestablished solar cell processing by photolithography, a conversion efficiency of 15-2% was reached on 73 cm2 area, highly doped offspec multicrystalline silicon substrates. The corresponding photogenerated current densities (Jsc) were well above 31 mA/cm2 for an active layer of only 20 m.