imec and Crystal Solar achieve 22.5 percent efficient kerfless nPERT cell

Only days after it was announced that Hanwha Q Cells will purchase 700 MW of kerfless wafers, over five years, from 1366 Technologies, a significant efficiency milestone has been reached in another U.S.-EU cooperation. Researchers from imec have been able to apply their PERT technology to an n-type wafer developed by Californian technology company Crystal Solar.

Silicon Valley-based Crystal Solar’s Direct Gas to Wafer technology can produce a 6-inch, 160 to 180 µm thick monocrystalline wafers, with a p-n junction formed during crystallization. Crystal Solar’s epitaxy wafer production process grows the monocrystalline silicon wafer from gas, with the company claiming that it is a high throughput process that can result in low cost/watt production.

The result announced by imec and Crystal Solar today has seen 156x156mm2 PV PERT cells produced using a wafer manufactured using the Direct WaferTM process, achieving a conversion efficiency of 22.5%. The two organizations claim it to be the highest efficiency achieved to date on a single junction PV cell based on an epitaxially grown wafer. imec reports that its PERT cell team adapted its nPERT cell technology to the Crystal Solar kerfless wafer.

"Imec’s n-PERT process included a selective front surface field realized by laser doping, advanced emitter surface passivation by Al2O3 and Ni/Cu-plated contacts," the Belgium research body set out in a release. It says a Voc of 700mV was achieved with the cells, indicating the high quality of the wafers and p-n junction.

"The combination of our advanced cell process and the innovative wafer manufacturing technique of Crystal Solar, is paving the way to the manufacturing of highly efficient solar cells at [a] lower cost than currently possible," said Jozef Szlufcik, PV Department Director at imec. "Using these kerfless wafers will be disruptive for the complete solar cell manufacturing value chain.”

T.S. Ravi, CEO of Crystal Solar added that efficiencies exceeding 23% can be achieved using imec’s PERT technology on its kerfelss wafers in the future.

“The epitaxial direct wafer growth with built in junctions approach represents a new paradigm in cell manufacturing with its unique ability to bypass significant steps in both wafer and cell manufacturing thereby dramatically reducing the capex and the overall cost per watt," said Ravi.

The challenge for Crystal Solar will now be to take its epitaxy wafer process into scale production. The time required for silicon crystal formation has been a challenge for epitaxy processes applied to PV in the past.

Hanwha Q Cells announced in October 2015 that it had achieved 19.1% efficiency PERC cells using 1366 Technology kerfless wafers. 1366 uses molten silicon for wafer production, rather than gas feedstock.