RAY TRACING ANALYSIS OF THE INVERTED PYRAMID TEXTURING GEOMETRY FOR HIGH-EFFICIENCY SILICON SOLAR-CELLS

Various texturing schemes to trap weakly absorbed light into solar cells have been proposed. light trapping in indirect band gap solar cells is necessary to increase the photogenerated current, thereby increasing the efficiency. Several common texturing geometries (slats, pyramids) have been examined to determine their light trapping characteristics. However, a detailed analysis of the geometry which produces the highest efficiency cells, the inverted pyramids, has not been reported. A quantitative analysis of the internal and external light trapping characteristics of the inverted pyramid geometry is presented for the first time. The internal characteristics show that the inverted pyramid geometry is able to confine the light better than the slats or upright pyramid designs, but possesses slightly poorer light trapping efficiency compared to a Lambertian front surface design. The path length enhancement for the inverted pyramid design is calculated to be almost-equal-to 1.40 (as compared to a planar cell) which is superior to that of the slat (almost-equal-to 1.13) and pyramid (almost-equal-to 1.30) designs. The short wavelength spectral response analysis indicates that almost-equal-to 37% of the incoming light experiences a triple bounce on the front surface of the inverted pyramid geometry, while no rays experience a triple bounce in the slat and upright pyramid geometries. The superior internal response coupled with the path length enhancement and reduced front surface reflectance makes inverted pyramids an attractive and efficient single sided geometric light trapping geometry.