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

This paper reports a substantially improved efficiency for a multicrystalli ne silicon solar cell of 19.8%. This is the highest ever reported efficienc y for a multicrystalline silicon cell, The improved multicrystalline cell p erformance 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 absor ption 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% o f infrared light is trapped in the substrate after the first two passes, co mpared with only 65% for the well known inverted pyramid structure. These o ptical features are considered to contribute to an exceptionally high short -circuit current density of 38.1 mA/cm(2). A further improvement is expecte d by using under-etched wells for these honeycomb cells.