Professor Venkat Selvamanickam at the University of Houston has received a $1,499,994 grant from the US Department of Energy (DOE) SunShot Initiative to produce high-efficiency, inexpensive thin-film photovoltaics.
The SunShot Initiative was created in 2011 to make solar energy cost-competitive with other forms of electricity by the end of the decade. Since then, it has funded more than 350 projects, with a goal of reducing the cost of solar electricity to about $0.06 per kilowatt-hour.
Selvamanickam (the M.D. Anderson Chair professor of mechanical engineering and director of the Applied Research Hub at the Texas Center for Superconductivity) says he began thinking several years ago about developing a technique to produce solar cells using a technique similar to the one he uses for coating semiconductors as thin films on low-cost metal substrates, based on a similar roll-to-roll manufacturing technology.
The most efficient solar cells are composed of a germanium wafer topped with gallium arsenide. But GaAs-on-Ge solar cells are expensive, Selvamanickam says, both because of the high costs of the Ge wafer and the manufacturing process. Also, the Ge wafers are small, requiring a large number to cover much area, so they are used mainly for space applications.
Picture: Photo of epitaxial GaAs thin film on flexible metal foil, and (b) schematic of the multilayer architecture developed to grow epitaxial GaAs thin films on metal foil.
Selvamanickam’s process involves using a metal foil tape with a germanium thin film (although another substance could be used as a base) and moving it at high speed with the roll-to-roll technology, coating it in a vacuum chamber with gallium and arsine vapor.
The work is being performed in Selvamanickam's Energy Devices Fabrication Laboratory at the University of Houston’s Energy Research Park (established in 2010 to conduct translational research to rapidly develop and transfer new technologies to industry). The new project with SunShot will be conducted in collaboration with the South Dakota School of Mines and Technology.
Selvamanickam’s team presented a proof-of-concept with his application to the DOE, showing high-quality GaAs thin films on metal foils (P. Dutta et al, Appl. Phys. Lett., vol105, p092104, 2014).
Other researchers have used roll-to-roll manufacturing technology for solar cells, but not with the germanium-GaAs materials so they had much lower efficiency, Selvamanickam says. Single-junction solar cells on germanium wafers produced with GaAs can operate at an efficiency of 28.5%, with a cost of several dollars per watt. Selvamanickam’s goal is to produce a solar cell that operates at 24% efficiency at a cost of 20 cents per watt.
