Researchers make a claim for 'most-efficient' CQD solar cell

30 July 2012

According to a statement, researchers from Toronto University in Canada and King Abdullah University of Science & Technology (KAUST) in Saudi Arabia created a solar cell out of inexpensive materials that was certified at a world-record 7.0 per cent efficiency.

‘Previously, quantum dot solar cells have been limited by the large internal surface areas of the nanoparticles in the film, which made extracting electricity difficult,’ said Dr Susanna Thon, a lead co-author of a letter on the research published in Nature Nanotechnology. ‘Our breakthrough was to use a combination of organic and inorganic chemistry to completely cover all of the exposed surfaces.’

Quantum dots are semiconductors only a few nanometres in size and can be used to harvest electricity from the entire solar spectrum — including both visible and invisible wavelengths. Unlike current slow and expensive semiconductor growth techniques, CQD films can be created quickly and at low cost, similar to paint or ink. This research paves the way for solar cells that can be fabricated on flexible substrates in the same way newspapers are rapidly printed.

The Toronto University cell represents a 37 per cent increase in efficiency over the previous certified record.

In order to improve efficiency, the researchers needed a way to both reduce the number of ‘traps’ for electrons associated with poor surface quality while simultaneously ensuring their films were very dense to absorb as much light as possible. The solution was a so-called ‘hybrid passivation’ scheme.

‘By introducing small chlorine atoms immediately after synthesising the dots, we’re able to patch the previously unreachable nooks and crannies that lead to electron traps,’ explained doctoral student and lead co-author Alex Ip. ‘We follow that by using short organic linkers to bind quantum dots in the film closer together.’

The advance could open up avenues for further research and improvement of device efficiencies, which could contribute to reliable, low-cost solar energy.

‘Our world urgently needs innovative, cost-effective ways to convert the sun’s abundant energy into usable electricity,’ said project leader Prof Ted Sargent. ‘This work shows that the abundant materials interfaces inside colloidal quantum dots can be mastered in a robust manner, proving that low-cost and steadily improving efficiencies can be combined.’