Researchers create tiny solar cells to power cell phones and MP3 players

In a USF lab illuminated by blue UV laser light, researchers are creating tiny organic solar cells that could power very small machines.

Called microelectromechanical systems (MEMS), the small machines include chemical sensors and small devices inside everyday technology, such as cell phones and MP3 players.

These solar cells, made of organic materials, have many advantages over traditional silicon solar cells. At only 1 square millimeter, about one-fourth the size of a grain of rice, the cells are not brittle like their silicon counterparts and can be produced on many different surfaces, such as fabrics, cars and microchips.

The size and flexibility of these organic cells are what make them so versatile, said Xiaomei Jiang, physics professor and lead researcher for the project.

“It is small, so it has the potential to go smaller,” Jiang said.

These solar panels are also lightweight, easy to carry and less expensive than the traditional silicon type.

Solar cells produce a current — a flow of eletricity and voltage — giving them the potential to produce this energy.

“(Silicon) solar cells are considered for their current source, not voltage,” said Jason Lewis, a graduate student working on the project.

The downside of MEMS device applications  is that they require a high voltage to run effectively — which the organic cells can provide. An 18-cell array on a solar panel can produce 7.8 volts, but Lewis said they are working on increasing this voltage. Fifteen volts are necessary to power a MEMS device.

Prototype solar cells, which are 2.2 square centimeters, were created on glass, Lewis said. The glass was coated with a compound called indium tin oxide, and then spun like spin-art with a material called positive photoresist. When a stencil is placed on the panel and exposed to UV light, the photoresist washes away in development, leaving the anode — or negative part of the solar cell — in place.

Solar cells, like batteries, can hold a charge, and have both negative and positive parts, Lewis said.

After several other intermediate steps, another stencil — a shadow mask — is placed on the panel. It is placed in a vacuum box, where the aluminum is heated until it evaporates and deposits in cut-out holes in the mask.

Aluminum — the cathode, or positive part of the cell — overlaps the anode, creating the 1-square-millimeter active area of the solar cell.

Lewis created several prototype panels, and the most efficient one with the highest voltage had 20 cells. Two of the cells shorted when it was manufactured, however, so only 18 cells could be accounted for, he said.

The USF research group is one of the leading labs in this type of solar cell development, and has made many recent improvements.

“We’re on the cutting edge,” Lewis said. “There is only one lab ahead of us in this research.”

The project has been running for six months and receives a little more than $20,000 from a USF internal grant, Jiang said.

They hope for more money, she said, because the product could benefit the community and the environment.