UC Berkeley researchers harness nanotechnology for solar panels

Jul 10, 2009 - Daily Californian/UWire

The answer to developing low-cost solar panels may lie in the creation of tiny 3-dimensional fibers that are 1,000 times smaller than a human hair.

UC Berkeley researchers have developed a method to grow nanopillars, which could eventually be used to produce more cost-efficient solar panels.

"A nanopillar is a 3-dimensional, wire material that is made of fiber," said researcher Zhiyong Fan, postdoctorate scholar in the electrical engineering and computer science department.

These nanopillars must grow through specific chemical reactions atop a piece of aluminum foil.

The potential for developing cheap solar panels out of the nanopillars stems from using aluminum as a substrate-rather than silicon-as is currently used in the roll-to-roll process that creates a solar cell, said lead researcher Ali Javey, assistant professor of electrical engineering and computer sciences.

In the researchers' own roll-to-roll process, they rolled semi-crystalline material inside an aluminum foil substrate, which, when unrolled, produces nanopillars that grow to create solar cells.

"If we can make such a roll-to-roll process with the nanopillars then our projected cost is 10 percent lower than projected (cost of other) solar cells," Javey said.

The price of the nanopillars may also be lower than that of the silicon-based counterparts because "the material is more tolerant to surface interface," Javey said.

Tolerance to surface interface means that the new solar technology would potentially lose fewer electrons than the silicon-based technology because of a smaller surface area-an advantage that would increase the energy efficiency of the solar cell.

"You can either increase the efficiency or decrease the material cost," Fan said. "Because our process is highly scalable, by using a larger metals we can easily make production more efficient and scale down the cost."

The researchers formulated a specific process for growing nanopillars atop aluminum.

In that process, a scientist creates a nanopillar "forest" through an interaction in which raw material fuels and vaporizes a powder in the chamber of a nanoparticle. A gold metal particle then acts as a catalyst by releasing a vapor of precipitate that gives rise to a nanopillar.

Fan likens the growth of nanopillars to the "bottom up" growth of a forest.

"A forest needs sunlight, water and pollen to grow from the earth. (Nanopillar) material similarly needs matter to grow so that you end up with a forest of (nanopillars)," Fan said.

Javey said he hopes to further develop the roll to roll process, which will fabricate solar cells from the nanopillars.

"We are moving forward to see if we can develop a roll to roll process ourselves: We know the challenges." Javey said.