February 13, 2013
New Manufacturing Method Could Drop Price Of Solar Cells
Lee Rannals for redOrbit.com — Your Universe Online
Solar cells are nothing new, but what may be coming is a technology to make a less expensive version of them.Silicon is used in both computer chips and solar cells, and both require a surface coating before use. This coating requires a lot of heat and energy to run in a passivation process, making it a costly step.
A group of MIT researchers wrote in the journal Advanced Materials they have found a way to passivate silicon at room temperatures, which could significantly help with the high price of manufacturing computer chips and solar cells.
The new process decomposes organic vapors over wires heated to 572 degrees Fahrenheit, but the silicon never goes above room temperature. Heating the wires requires less power than illuminating an ordinary light bulb, so the energy cost is kept low.
Tonio Buonassisi, an associate professor of mechanical engineering and a researcher on the project, said silicon-nitride passivation is one of the more expensive parts, and one of the more finicky parts in the processing of silicon for solar cells. By replacing part of the silicon nitride's functionality with an organic layer, Buonassisi says it has "potential to be a big win."
Without passivation, silicon's surface is oxidized as soon as it´s exposed to air, which can impede its performance as a solar cell. The team tested silicon chips with the new polymer coating in place for more than 200 hours and observed no degradation at all in performance.
Because the silicon chip making process has a low temperature, it can be combined with other materials, such as organic compounds, that would be normally destroyed at higher temperatures. This enables new applications for the chips.
As the cost of manufacturing silicon solar cells begins to drop, the savings helps make the alternative to other sources of electricity a more viable option.
According to Buonassisi, lowering the cost of manufacturing equipment is one of three steps needed to help try and drive down the price of solar modules. The next step, he said, is to scale up the process from laboratory-scale to production levels.
University of Michigan researchers also reported a method, similar to the MIT teams, last month, of making silicon crystals at just 180-degrees fahrenheit, which is the internal temperature of a cooked turkey.
During this study, Stephen Maldonado, professor of chemistry and applied physics at the University of Michigan, and colleagues made a solution containing silicon tetrachloride and altered it over a liquid gallium electrode. This is similar to when water is super-saturated with sugar and that sugar spontaneously forms crystals. However, instead of water, they used liquid metal, and instead of sugar, silicon.
“The liquid metal is the key aspect of our process,” Maldonado said. “Many solid metals can also deliver electrons that transform silicon tetrachloride into disordered silicon, but only metals like gallium can additionally serve as liquids for silicon crystallization without additional heat.”
When considering both papers, published just weeks apart, it becomes obvious a day is coming when solar cell energy could become a more lucrative option for a home.