Wednesday, September 8, 2010

MIT boffins unveil self-healing solar cell

For years scientists have managed to develop solar cells that are highly efficient in laboratory conditions, but quickly deteriorate when asked to cope with direct sunlight – which constitutes something of a drawback for a solar panel.

Now a team of researchers from the Massachusetts Institute of Technology (MIT) reckon they may have found the solution to the problem of deteriorating solar cells following the demonstration of a new cell design that manages to repair itself.

The cell mimics the ability of plants to convert sunlight into energy at the same time as continuously breaking down light-capturing molecules and reassembling them from scratch in order to avoid the debilitating effects of sunlight.

Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering, who led the research team, said the cell was "basically imitating tricks that nature has discovered over millions of years", such as plants' " reversibility, the ability to break apart and reassemble".

The cell uses synthetic molecules known as phospholipids that form disks which then provide structural support to proteins that respond to light. The molecules then create "reaction centres" that release electrons when hit by light particles. When suspended in a solution these reaction centres spontaneously attach themselves to carbon nanotubes that hold the disks in place and also act as wires that can transmit the released electrons.

The research team then added a surfactant to the self-assembling mixture, which resulted in the seven components that make up the system breaking apart. Once the surfactant, which MIT said was similar to that used to break up the BP oil spill in the Gulf, was removed from the mixture using a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

The team then ran the cell through the same cycle of assembly and disassembly repeatedly over a 14-hour period and recorded no loss of efficiency.

Strano said that the initial experiment delivered very low levels of efficiency, because the concentration of the molecular structures in the solution was very low. However, the efficiency of each individual structure stood at around 40 per cent, double that of the most efficient solar cells currently available, while the team believes that, theoretically, the structures could reach close to 100 per cent efficiency. MIT said the team is now working on how to increase the concentration of the solution.

It is likely to take years to develop commercially available solar cells based on the technology, but the breakthrough suggests that one of the most significant technical challenges faced by emerging nanomaterial-based solar technologies could be overcome.

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