A 19.8% efficient honeycomb multicrystalline silicon solar cell with improved light trapping

Abstract

This paper reports a substantially improved efficiency for a multicrystalline silicon solar cell of 19.8%. This is the highest ever reported efficiency for a multicrystalline silicon cell. The improved multicrystalline cell performance results from enshrouding cell surfaces in thermally grown oxide to reduce their detrimental electronic activity and from isotropic etching to form a hexagonally-symmetric "honeycomb" surface texture. This texture, largely of inverted hemispheres, reduces reflection loss and improves absorption of infrared light by effectively acting as a randomizer. Results of a ray tracing model are presented, with the notable finding that up to 90% of infrared light is trapped in the substrate after the first two passes, compared with only 65% for the well known inverted pyramid structure. These optical features are considered to contribute to an exceptionally high short-circuit current density of 38.1 mA/cm/sup 2/. A further improvement is expected by using under-etched wells for these honeycomb cells.