A 22.5% cell efficiency is reported for n-type passivated emitter, rear totally-diffused (nPERT) silicon solar cells manufactured on 6-inch (150 mm) mono-crystalline epitaxially grown kerfless wafers. This development, along with an open-circuit voltage of 700 mV, is claimed by Belgium-based research institute imec and Crystal Solar. Their collaboration demonstrates one of the highest efficiencies to date for homojunction solar cells on epitaxially grown silicon wafers.

Crystal Solar’s high throughput epitaxial reactor.The initiative was based on Direct Gas to Wafer manufacturing technology devised by Crystal Solar of Santa Clara, Calif. The process supports direct conversion of feedstock gas to mono crystalline silicon wafers by high throughput epitaxial growth. Capital cost savings and efficiency gains stem from elimination of polysilicon, ingoting, and wire-sawing steps. The result is production of high quality p-n junctions in-situ at lowest cost per watt for wafers.

The efficient nPERT Si solar cell process developed by imec was modified to align with the properties of Crystal Solar’s kerfless wafers and to fabricate 156x156mm² cells on 160 to 180 um thick grown n-type wafers with built-in rear p+ emitter. Imec’s nPERT process includes a selective front surface field realized by laser doping, advanced emitter surface passivation by Al₂O₃ and Ni/Cu plated contacts.