UF Team Helping To Create Solar Cells Thinner Than Human Hair

July 21, 1999

GAINESVILLE — University of Florida engineers are pioneering an inexpensive method for making a new breed of exceptionally thin and cheap solar cells expected to make solar power a more widespread source of electricity in the new millennium.

The cells, known as “thin-film solar cells,” are 100 times thinner and potentially lighter than today’s silicon cells. They also require less semiconductor materials, an attribute that opens the door for the cells to be made cheaply and in great quantity.

“The material cost is very minimal,” said Sheng Li, a UF professor of electrical and computer engineering and part of a four-member UF faculty team at work on the process. “This is a very promising technology for solar cells.”

The UF research comes at a time when the market for solar cells is in a strong growth spurt. For the past several years, the industry has an annual growth rate of 15 to 20 percent, similar to that of the booming semiconductor and computer industries. Total sales reached the $1 billion mark in 1998, according to industry publications.

Solar cells’ advantage is that they produce “green” power without harmful emissions. Also, they can generate power for a house or small business on site, reducing electrical demand on power plants and electrical grids.

Traditional silicon cells, however, require relatively large amounts of semiconducting materials, making them expensive to manufacture and driving up their cost in the marketplace. They also are heavy and unwieldy, limiting their potential applications, Li said.

The UF researchers hope to get around these problems through the thin-film cells, which can be created with “pennies’ worth” of materials on flexible surfaces such as plastic. Where traditional solar cells use wafers similar to computer chips, thin film cells use thin layers of semiconductor material. Thin-film cells, however, have a far more complex chemical structure and are more difficult to make than traditional cells, attributes that have limited their production and commercialization to date.

Scientists and engineers at more than a dozen universities, government labs and corporations are exploring several different thin-film solar cell technologies as part of a major initiative sponsored by the National Renewable Energy Laboratory, a government lab that seeks to develop renewable energy technologies and improve energy efficiency.

The UF team, part of the “Thin Film Partnership program,” is focusing on a technology that uses a compound semiconductor called “copper indium diselenide,” or “CIS.”

The technology involves depositing an extremely thin layer of CIS on a specially prepared material such as glass, Li said. Two to 3 microns thick, the semiconductor layer is thinner than a human hair and 100 times thinner than conventional solar cells, he said.

Researchers elsewhere have demonstrated CIS cells can convert as much as 18 percent of sunlight to electricity, about the efficiency of the most efficient traditional silicon cells, according to the National Renewable Energy Laboratory. But there still are major challenges to overcome in manufacturing the cells.

“They have a more complicated structure and require more complicated processing,” said Tim Anderson, chairman of the UF chemical engineering department and member of the CIS team. “Our role is to better understand the processing and transfer the technology to industry.”

The UF team also is experimenting with ways to simplify the manufacturing process, Li said. Three years into the six-year project, the team has used a simpler, cheaper process to make CIS cells with efficiencies in the range of 8 to 10 percent — good progress toward the project’s goal of 13 to 15 percent efficiency, Li said. He added that he expects CIS cells to be widely available on the market in less than 10 years.

The National Renewable Energy Laboratory is providing about $1.6 million for the research. The other UF team members are Paul Holloway, a professor of materials science and engineering, and Oscar Crisalle, an associate professor of chemical engineering.