Increased photogeneration in thin silicon concentrator solar cells

Abstract

Recent progress in silicon concentrator solar cells has resulted in several designs capable of 25-percent efficiency with one group reporting 28 percent under 14 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of incident power at 25°C. It has been shown that further improvement is possible by restricting the sunlight acceptance angle of the cell. In this letter, a practical implementation which is equivalent in its effect is proposed which results in an increased utilization of weakly absorbed near-bandgap light. This increased absorption is obtained by placing the cells in a cavity with a small entrance aperture. An analysis is given based upon work on the acceptance angle enhancements by Campbell and Green. The design is expected to improve the efficiencies of existing solar cells to 30 percent. If used in conjunction with previously proposed cell improvements, the efficiencies will be improved towards 33 percent, very near the limit efficiency of 36 percent. This design also has the effect of decreasing the differences in performance between the leading candidate concentrator cell designs and diminishing the dependence of the efficiencies on the cell texturization and bulk carrier lifetimes.