Researchers at Rensselaer Polytechnic Institute have developed a new nanoengineered antireflective coating that boosts the amount of sunlight captured by solar panels to near-perfect levels (>96%) and allows those panels to absorb the entire solar spectrum from nearly any angle. The discovery could help enable the wider use of solar power.
A paper describing the work led by Professor Shawn-Yu Lin is published in the journal Optics Letters.
An untreated silicon solar cell only absorbs 67.4% of sunlight shone upon it. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.
After a silicon surface was treated with Lin’s new nanoengineered reflective coating, however, the material absorbed 96.21% of sunlight shone upon it. This gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared. Lin’s new coating also absorbs sunlight evenly and equally from all angles.
Most surfaces and coatings are designed to absorb light and transmit light from a specific range of angles. This same is true of conventional solar panels, which is why some industrial solar arrays are mechanized to slowly move throughout the day so their panels are perfectly aligned with the sun’s position in the sky. Without this automated movement, the panels would not be optimally positioned and would therefore absorb less sunlight. The tradeoff for this increased efficiency, however, is the energy needed to power the automation system, the cost of upkeeping this system, and the possibility of errors or misalignment.
Typical antireflective coatings are engineered to transmit light of one particular wavelength. Lin’s new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to “bend” the flow of sunlight to an angle that augments the coating’s antireflective properties. Each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it.
The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle. The nanorods were attached to a silicon substrate via chemical vapor disposition, and Lin said the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.
Along with Lin and Kuo, co-authors of the paper include E. Fred Schubert, Wellfleet Senior Constellation Professor of Future Chips at Rensselaer; Research Assistant Professor Jong Kyu Kim; physics graduate student David Poxson; and electrical engineering graduate student Frank Mont.
Funding for the project was provided by the US Department of Energy’s Office of Basic Energy Sciences, as well as the US Air Force Office of Scientific Research.
(A hat-tip to Jeremy!)
Mei-Ling Kuo, David J. Poxson, Yong Sung Kim, Frank W. Mont, Jong Kyu Kim, E. Fred Schubert, and Shawn-Yu Lin (2008) Realization of a near-perfect antireflection coating for silicon solar energy utilization. Optics Letters, Vol. 33, Issue 21, pp. 2527-2529 doi:10.1364/OL.33.002527