New texturing geometry for producing high efficiency solar cells with no antireflection coatings

Various schemes to trap weakly absorbed light into solar cells have been proposed. These schemes include texturing the cell, texturing the cover glass and geometric arrangements of the individual cells. The perpendicular slats geometry is considered to be the best cell texturing design for light trapping. In this paper a new cell surface texturing design is proposed which, without the use of anti-reflection coatings, can outperform the perpendicular slats geometry with a double layer anti-reflection coating by virtue of efficient internal light trapping and a decrease in the front surface reflectance. The single sided texture uses three perpendicular planes on the front surface and a planar back surface. The three perpendicular planes provide a triple bounce for the incoming light and efficient confinement for light which has entered the cell. TEXTURE, a raytracing program for textured cells, was used to predict the performance of this new design. A quantitative comparison with other texturing schemes is also provided. It is shown that for a cell without an anti-reflection coating on the front and a 98% effective back surface reflector, the new design produces a maximum short circuit current density of 40.99 mA/cm2 as compared to 41.46 mA/cm2 and 35.16 mA/cm2 for the perpendicular slats geometry and flat surfaces, respectively, with a conventional single layer AR coating on the front. Effects of different front surface reflection coefficients are examined to show that as the front reflectance is decreased by improved antireflection coatings, the importance of the triple bounce is reduced and most promising surface texturing schemes approach the same value of maximum current.