November 25, 2008--Using computer modeling and a variety of advanced chip-manufacturing techniques, a team of physicists and engineers at the Massachusetts Institute of Technology (MIT; Cambridge, MA) have applied an antireflection coating to the front, and a novel combination of multi-layered reflective coatings and a tightly spaced array of lines (diffraction grating) to the backs, of ultrathin silicon films to boost the cells' output by as much as 50%.
The team ran thousands of computer simulations in which they tried out variations in the spacing of lines in the grid, the thickness of the silicon and the number and thicknesses of reflective layers deposited on the back surface. "We use our simulation tools to optimize overall efficiency and maximize the power coming out," Bermel said.
"The simulated performance was remarkably better than any other structure, promising, for 2 µm thick films, a 50% efficiency increase in conversion of sunlight to electricity," said Lionel Kimerling, the Thomas Lord Professor of Materials Science and Engineering, who directed the project.
The simulations were then validated by actual lab-scale tests. "The final and most important ingredient was the relentless dedication of graduate student Lirong Zeng, in the Department of Materials Science and Engineering, to refining the structure and making it," Kimerling said. "The experiments confirmed the predictions, and the results have drawn considerable industry interest." The team will report the first reduction to practice of their findings on Dec. 2 at the Materials Research Society's annual meeting in Boston. A paper on their findings has been accepted for publication in Applied Physics Letters.
--Posted by Gail Overton
For more information, visit www.mit.edu.