MIT creates plant-inspired solar cell

Researchers in the US are hoping to improve the efficiency of solar power cells using plant-inspired technology that repairs itself when damaged by the sun.

Sunlight can degrade the materials used in many new non-silicon solar generation systems, reducing their efficiency to as little as 10 per cent of their initial performance, according to scientists at the Massachusetts Institute of Technology (MIT).

To combat this problem, the team has created a complex structure of molecules that turns sunlight into electricity and that can break down and then reassemble itself with replacement molecules when another chemical is added.

‘In the solar energy field, there is this focus on the immediate efficiency of new devices,’ team leader Prof Michael Strano told The Engineer. ‘But few people are asking questions about what happens after several hours or even weeks.

‘It’s a tedious problem but the truth is that in photoelectrochemical cells you see a precipitous drop-off in efficiency in just a few hours.’

Strano’s solar cell contains a synthetic complex of seven components in solution with electrochemical mediators ferrocyanide and ubiquinone, which help to carry electrons to and from the cell’s electrodes.

The complex itself consists of molecules that release electrons when struck by particles of light, held on discs of other molecules called phospholipids. These spontaneously attach themselves to carbon nanotubes, which hold the discs in uniform alignment and conduct the charge away from them.

Under Strano’s system, a surfactant similar to oil-dispersing chemicals is periodically added to the cell, causing the complex to break down. The solution is then passed through a membrane, removing the surfactant and allowing the complex to reassemble, with new molecules replacing any that were damaged by the sun.

The idea was inspired by the natural repair system used by plants when they photosynthesise. When sunlight damages the proteins in chloroplasts – the part of plant cells where photosynthesis happens – the molecules naturally reassemble to restart the process.

‘The human approach is to filter out damaging parts of the sun,’ said Strano. ‘What nature does is harnesses the full solar spectrum, but has figured out a scheme to continuously rebuild the parts that degrade.’

Although Strano’s cell had to go through periods of repair and so electricity production was intermittent, the process helped increase energy efficiency by 300 per cent.

The next step will be to increase the concentration of the complex in solution while maintaining the repair mechanism.

‘For that, we’re looking at plants as well,’ said Strano. ‘Plants have interesting structures that they form to display these proteins to harvest light. So we think we’re going to be able to continue to learn from nature and make man-made equivalents.’

He hopes to have a desktop prototype device ready in two to three years, after which it could begin to be developed commercially.

The research, published in Nature Chemistry, was supported by grants from the MIT Energy Initiative and the Department of Energy, as well as funding from Italian oil company Eni.

A low-cost solar cell that imitates photosynthesis opens up new applications for photovoltaics. Click here to read more.