Toronto, ON, Canada--Led by University of Toronto (U of T) engineering professor Ted Sargent, both U of T and King Abdullah University of Science & Technology (KAUST) researchers have created the most efficient colloidal quantum-dot (CQD) solar cell to date—with a record-breaking 7.0% efficiency. The CQD is a type of semiconductor only a few nanometers in size that is used to harvest electricity from the entire solar spectrum, including both visible and infrared wavelengths, and is fabricated using low-cost manufacturing techniques that make quantum dots a cost-effective alternative to other solar-cell technologies.
"Our world urgently needs innovative, cost-effective ways to convert the sun's abundant energy into usable electricity,” said 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." The findings are published in Nature Nanotechnology.
"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 post-doctoral fellow Susanno Thon, a lead co-author of the paper. "Our breakthrough was to use a combination of organic and inorganic chemistry to completely cover all of the exposed surfaces." 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 in mass quantities.
The U of T cell represents a 37% 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 synthesizing 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."
Work led by professor Aram Amassian of KAUST showed that the organic ligand exchange was necessary to achieve the densest film. "The KAUST group used state-of-the-art synchrotron methods with sub-nanometer resolution to discern the structure of the films and prove that the hybrid passivation method led to the densest films with the closest-packed nanoparticles," said Amassian.
SOURCE: University of Toronto; https://www.utoronto.ca/news/new-solar-cell-sets-world-record-efficiency