The U.S. Energy Department's National Renewable Energy Laboratory has developed an innovative furnace that sharply boosts solar cell efficiency, speeds up the processing time and could ultimately help cut costs.
Within the manufacturing process, solar cells are tested for mechanical strength, oxidized, annealed, purified, diffused, etched and layered. Furnaces are common in large solar cell factories because heat is the primary tool used in each one of those steps. Until now, factories have relied on rapid-thermal processing furnaces that use radiant or infrared heat to boost the temperature of silicon wafers up to 1,000 degrees Celsius within several seconds, according to the NREL.
The NREL has put a new spin on the furnace by using optics to heat and purify solar cells, which allows greater control and precision. The Optical Cavity Furnace (not the most inviting name) encloses an array of lamps within a reflective chamber. The highly reflective ceramics, which are placed in a complex geometric design, eliminate all energy loss and help keep the temperature consistent and uniform throughout the furnace.
The cavity design uses about half the energy of a conventional thermal furnace because the wafer itself absorbs what would otherwise be energy loss, the NREL said. The furnace operates in the same way a microwave oven does by dissipating energy only on the object and not on the container.
Unlike conventional furnaces, the optical cavity process heats the wafers at a slower rate, which lowers the power requirements and energy loss. Meaning it can boost efficiency and lower costs at the same time.
The upshot? While researchers continue to tweak the furnace and make improvements, they expect to be able to hike efficiency by 4 percentage points -- a mammoth leap forward for the industry.
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, NREL Principal Engineer Bhushan Sopori said in a news feature on its website. That's huge.
The NREL and AOS Solar also are building a manufacturing-sized optical cavity furnace capable of processing 1,200 wafers an hour.
Photo: NREL/Dennis Schroeder
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