Optical Cavity Furnace Could Cut Solar Costs

A new furnace system for manufacturing solar cells has been developed — an advance that could boost efficiency and cut the cost of producing solar panels in the future.

The Optical Cavity Furnace (OCF) is designed to replace the standard thermal or rapid-thermal-processing furnaces that use radiant or infrared heat with a technique that uses optics to heat and purify solar cells at unmatched precision while sharply boosting the cells’ efficiency.

The cavity inside the Solar Optical Furnace glows white hot during a simulated firing of a solar cell. (Images: Dennis Schroeder)

The system, developed by the US Department of Energy’s National Renewable Energy Laboratory (NREL), can blast heat up to 1000 ºC, a temperature used to remove impurities from silicon solar wafers. And, because various cell types require various heat treatments, the OCF system can be programmed to fit a specific solar cell configuration and temperature profile.

An NREL colleague inserts a multicrystalline silicon solar cell sample into the Optical Cavity Furnace, while Bhushan Sopori gets ready to read its analysis on his computer screen.

NREL’s system encloses an array of lamps within a highly reflective chamber to achieve an unprecedented level of temperature uniformity. It virtually eliminates energy loss by lining the cavity walls with superinsulating, highly reflective ceramics and by using a complex optimal geometric design. The cavity design uses about half the energy of a conventional thermal furnace because, in the OCF, the wafer itself absorbs what would otherwise be energy loss. As with a microwave oven, the OCF dissipates energy only on the target, not on the container.

Various configurations of the OCF use the benefits of optics to screen wafers that are mechanically strong to withstand handling and processing, remove impurities (called impurity gettering), form junctions, lower stress, improve electronic properties and strengthen back-surface fields.

Sopori discusses the capabilities of the Optical Cavity Furnace with colleagues Vishal Mehta and Peter Rupnowski.

“Our calculations show that some material that is at 16 percent efficiency now is capable of reaching 20 percent if we take advantage of these photonic effects,” said Bhushan Sopori, NREL principal engineer. “That's huge.”

Meanwhile, NREL and its private-industry partner, AOS Inc., are building a manufacturing-size OCF capable of processing 1200 wafers an hour.

NREL said it has cooperative research and development agreements with several of the world’s largest solar-cell manufacturers, all intrigued by the OCF’s potential to boost quality and lower costs.

For more information, visit: www.nrel.gov