Solar cell mimics plants to self-repair

Posted by Emma Woollacott

Using carbon nanotubes and DNA, researchers have created a new type of solar cell designed to self-repair like natural photosynthetic systems in plants.

Unlike the self-repairing solar cells developed by MIT last year, the Purdue University design exploits the unusual electrical properties of single-wall carbon nanotubes, using them as 'molecular wires' in light harvesting cells.

"We've created artificial photosystems using optical nanomaterials to harvest solar energy that is converted to electrical power," says Jong Hyun Choi, an assistant professor of mechanical engineering at Purdue University. "I think our approach offers promise for industrialization, but we're still in the basic research stage."

Photoelectrochemical cells convert sunlight into electricity and use an electrolyte to transport electrons and create the current. The cells contain light-absorbing, chlorophyll-like dyes called chromophores - but these degrade after exposure to sunlight.

The new technology overcomes this problem by continuously replacing the photo-damaged dyes with new ones, just as plants do. It could lead to a new type of photoelectrochemical cell that continues operating at full capacity indefinitely, as long as new chromophores are added.

The carbon nanotubes work as a platform to anchor strands of DNA. The DNA itself is engineered to have specific sequences of building blocks called nucleotides, enabling them to recognize and attach to the chromophores.

"The DNA recognizes the dye molecules, and then the system spontaneously self-assembles," Choi said.

When the chromophores need replacing, they could be removed by using chemical processes or by adding new DNA strands with different nucleotide sequences, kicking off the damaged dye molecules. New chromophores would then be added.

Unfortunately, using natural chromophores is difficult, and they need to be harvested and isolated from bacteria - expensive on an industrial scale, says Choi.

"So instead of using biological chromophores, we want to use synthetic ones made of dyes called porphyrins," he said.