Volunteers Help Scientists in Search for Cheap Solar Cells

July 15,2013

Solar cells remain a relatively expensive investment for ordinary consumers of electric power. But a group of scientists at Harvard University is looking for cheaper, organic solar cells, which could be painted on rooftops and building facades. In their research, they are employing the help of thousands of volunteers around the world.

Most of today's solar cells are silicone-based and their manufacture requires sophisticated machinery and expertise. An average home in the United States uses between 20 and 24 kilowatt hours of electricity every day. And it may cost up to $20,000 to buy and install solar panels that can produce that much energy. While economical in the long run, it is an expense many cannot afford.

But a group of researchers in the Harvard Clean Energy Project is looking for cheaper, carbon-based compounds that could substantially lower that price. Project head Alan Aspuru said that a carbon-based solar cell would have to be about 10 percent efficient to make an impact.

"This basically means that 10 percent of the sunlight that hits the device is converted into energy. There's about three, or four, or maybe five - a handful of molecules that we know about, that already have this efficiency. And this has been discovered in the last year or a couple of years," said Aspuru.

Aspuru says today's most commonly used silicone-based solar cells also do not have a very high efficiency, just about 15 percent. More-efficient solar cells do exist, but they are used mainly on satellites, due to their high cost. But cheap carbon-based solar cells could cover large surfaces - compensating for their low efficiency.

Researchers already have identified 2.3 million carbon-based compounds, out of which 35,000 potentially could have efficiency above 10 percent.

"That does not necessarily mean that those 35,000 molecules, all of them would be above 10 percent efficient. For a solar cell that basically means they could potentially be, and more research has to be done on them," he said.

Aspuru said further analysis of those compounds requires large computing power, which his group is getting from volunteers around the world who donate their computers' time to a "virtual supercomputer" project.

"In my case, in partnership with [the] IBM project for the World Community Grid, hundreds of thousands of people that are registered in the database of IBM are on and off computing for many projects, including ours," he said.

Researchers are hopeful their findings will spur innovation, and that based on this research, experimental laboratories around the world will be able to come up with new materials.

Results so far are encouraging. The Clean Energy Project already has discovered a powerful organic semiconductor named DA2T. It's the second best semiconductor reported in scientific literature.