“A lot of other low-cost approaches don’t produce high-performance devices, but in this case great performance is maintained,” says Yi Cui, professor of materials science and engineering at Stanford University. “And in the end it’s flexible, something you can’t get with conventional processing,” he adds. Rogers developed a similar method for making large area, flexible silicon electronics a few years ago, and adapted the chemistry to work with gallium arsenide. Cui says that the latest work shows that the method should work with any crystalline semiconducting materials, as long as the right chemistry can be found so that the etching step affects only the sacrificial layer.
The multilayer technique “is quite attractive since it makes the process highly scalable and potentially cost-effective, making the potential use of gallium arsenide for large-scale photovoltaics a reality,” says Ali Javey, professor of electrical engineering and computer science at the University of California, Berkeley.
Semprius is using the process to make multilayer, microscale concentrated solar modules with efficiencies as high as 37 percent. These modules should produce power at a cost of about $2 to $3 per watt after installation. Joe Carr, the company’s CEO, says Semprius’s pilot plant will be operational by the end of this year, at which time it will begin making its first products. The company has funding from the U.S. Department of Energy and a development agreement with Siemens.
Rogers says he pursued solar power as an initial application because photovoltaic sales are so cost-sensitive. His research group will continue to develop other devices, and it also plans to adapt the technique to other materials. He also hopes to adapt the method to gallium nitride, which works well in the visible spectrum and can be used to make solid-state lighting.