The change to nickel can reduce the cell's already low material costs by 40 to 80 percent, says Lukasz Brzozowski, the director of the Photovoltaics Research Program in Professor Ted Sargent's group. They present their research in the July 12, 2010 issue of Applied Physics Letters, which is published by the American Institute of Physics (AIP).
Quantum dots are nanoscale bits of a semiconductor material that are created using low-cost, high-throughput chemical reactions in liquid solutions. Since their properties vary according to their size, quantum dots can be made to match the illumination spectrum. Half of all sunlight, for example, is in the infrared wavelengths, most of which cannot be collected by silicon-based solar cells. Sargent's group has pioneered the design and development of quantum dot solar cells that gather both visible and infrared light. They have reached a power-conversion efficiency as high as 5 percent and aim to improve that to 10 percent before commercialization.
At first, nickel did not appear to do the job. "It was intermixing with our quantum dots, forming a compound that blocked the current flow from the device," says Dr. Ratan Debnath, first author on the group's paper. Adding just one nanometer of lithium fluoride between the nickel and the dots created a barrier that stopped the contamination, and the cell's efficiency jumped back up to the expected level.
This is the latest of several recent solar-cell milestones by the Canadian researchers. "We have been able to increase dramatically the efficiency of our photovoltaics over the last several years and continue to hold the performance world records," Professor Sargent said.
The article, "Depleted-Heterojunction Colloidal Quantum Dot Photovoltaics Employing Low-Cost Electrical Contacts" by Ratan Debnath, Mark Theodore Greiner, Illan Kramer, Armin Fischer, Jiang Tang, Aaron Barkhouse, Xihua Wang, Larissa Levina, Z. H. Lu and Edward H. Sargent will appear in the journal Applied Physics Letters. See: http://apl.aip.org/applab/v97/i2/p023109_s1
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This work was supported through an E8 scholarship, an award made by King Abdullah University of Science and Technology (KAUST), and funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chairs, and the Canada Foundation for Innovation.
ABOUT APPLIED PHYSICS LETTERS
Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. Content is published online daily, collected into weekly online and printed issues (52 issues per year). See: http://apl.aip.org/
The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world's largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.
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