Technology

Self-Assembling, Self-Repairing Solar Cells Pass Endurance Test

80beatsBy Joseph CalamiaSep 8, 2010 5:00 PM

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Faced with the sun's damaging rays, new biological solar cells can repair themselves, regaining their maximum efficiency when some competitors might fade. In their current form these biological solar cells, made with a bacterium's photosynthesis hub and carbon nanotubes, only reach a small fraction of the efficiency seen in the best traditional solar cells. But their ability to reinvent themselves by shedding damaged proteins and reassembling to regain their maximum efficiency could be a useful feature for future solar cells. The researchers, who published their work in Nature Chemistry, used a bacterium's natural light collection center to generate solar power, used proteins and lipids to make supporting disc forms, and employed conducting carbon nanotubes to channel away electric current. This set of materials chemically clumps together, making the cells self-assembling.

The spontaneous assembly occurs thanks to the chemical properties of the ingredients and their tendency to combine in the most energetically comfortable positions. The scaffolding protein wraps around the lipid, forming a little disc with the photosynthetic reaction center perched on top. These discs line up along the carbon nanotube, which has pores that electrons from the reaction center can pass through. [Science News]

The components' chemical properties also allow the solar cells to repair themselves. When the cells start to lose efficiency, the researchers pump a detergent called a surfactant into the solar cells' liquid home in order to make the pieces spread apart, and then add new proteins. When they remove the surfactant, the structures automatically recombine with new proteins instead of the damaged ones and regaine their initial efficiency.

The authors simply added a bit of detergent to the solution, and its ability to generate a photocurrent plunged.... They then added a bit more proteins, and pulled the detergent back out of the solution by dialysis. As predicted, any damaged proteins were not incorporated into the newly reformed photosynthetic complexes. Performance went right back to its initial peak once the detergent was gone before declining again along a similar trajectory. This behavior kept going through at least four cycles of detergent addition, with the system regenerating to the same peak each time. [Ars Technica]

These self-repairing natural systems are a good starting point for researchers who are investigating ways to make solar cells last longer, making them even more sustainable.

"Sunlight, when it hits oxygen, is very damaging," explained Michael Strano, the Massachusetts Institute of Technology chemical engineer who led the research. "It's the reason why we age, and the reason why when we leave paper or plastic out in the sun, it fades.... There's a kind of a horse race among scientists around the world to make the highest efficiency cell, but very few people are asking what happens with that cell when you plug it in for a few hours or for a week or for months," he said. [BBC]

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Image: Nature / Michael S. Strano et al.

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