New method could lead to solar cells with greater efficiency

Washington, Nov 25 : Researchers at MIT (Massachusetts Institute of Technology) have developed a method that could lead to solar photovoltaic cells with greater efficiency and lower cost.

Using computer modeling and a variety of advanced chip-manufacturing techniques, researchers have applied an antireflection coating to the front, and a novel combination of multi-layered reflective coatings and a tightly spaced array of lines to the backs of ultrathin silicon films to boost the cells' output by as much as 50 percent.

The carefully designed layers deposited on the back of the cell cause the light to bounce around longer inside the thin silicon layer, giving it time to deposit its energy and produce an electric current.

Without these coatings, light would just be reflected back out into the surrounding air, according to Peter Bermel, a postdoctoral researcher in MIT's physics department who has been working on the project.

"It's critical to ensure that any light that enters the layer travels through a long path in the silicon," Bermel said. "The issue is how far does light have to travel (in the silicon) before there's a high probability of being absorbed and knocking loose electrons to produce an electric current," he added.

The team began by running 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-micrometer-thick films, a 50 percent 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.

According to Kimerling, "The experiments confirmed the predictions, and the results have drawn considerable industry interest."

The work is just a first step toward actually producing a commercially viable, improved solar cell.

That will require additional fine-tuning through continuing simulations and lab tests, and then more work on the manufacturing processes and materials.

"If the solar business stays strong, implementation within the next three years is possible," Kimerling said.

ANI