Out of sight, but not out of power
Alternative energy will have a brighter future if researchers, like Karin Hinzer, can enable solar energy technology to see more sunlight.
by Tim Lougheed
When we talk about solar energy, most of us naturally think of the sunlight we can see. But a great deal of sunlight is simply invisible to us, striking the earth as electromagnetic energy at ultraviolet or infrared wavelengths. Engineers can see a broader spectrum that will improve the output of the panels we currently use to capture this energy and convert it into electricity.
Karin Hinzer, associate professor at the School of Electrical Engineering and Computer Science, has been studying this prospect for more than a decade. She aban¬doned life as a physicist in the late 1990s to begin working with lasers for Nortel Networks. Hinzer eventually came to the University of Ottawa in 2007 as holder of the Canada Research Chair in Photonic Nanostructures and Integrated Devices. There, she established the SUNLab, one of the country’s leading solar technology research facilities.
Along the way she has become a key member of the Photovoltaic Innovation Network, a nation-wide collaboration between industry, government and the research community created to make progress in solar power systems. While these systems have become commercially available and widely installed, Hinzer maintains that the technology remains far from realizing its full potential.
“The traditional panels that you buy are a single p-n junction,” she explains, referring to the circuit commonly used in the semiconductor devices that drive modern electronics. “Light comes into the semiconductor and gets absorbed. The thing is, only part of the solar spectrum gets absorbed.”
This limitation explains why solar panels currently on the market have an efficiency of about 20%, which means that only this percentage of the energy arriving at the panel is converted into useable electricity. Hinzer’s work focuses on developing a much more complex design for these panels aimed at raising their level of efficiency to as much as 40%.
Arrays of mirrors and lenses are installed within the panel, concentrating the amount of sunlight until it can reach up to 1,000 times the intensity of the original sunbeam. Rather than falling on a single semi¬conductor, energy from the light hits a device with three semiconducting layers. The top consists of a gallium-indium-phosphide compound to absorb ultraviolet radiation, the middle is a gallium-arsenide compound responding to the visible spectrum and the bottom is a germanium compound that is sensitive to infrared light.
The underlying principle is simple: each layer samples a different part of the spectrum, thereby increasing the total amount of electricity that is generated. However, constructing such an intricate semiconductor package—which will allow parts of the solar spectrum light to pass through its various layers—is far from simple. Hinzer and her colleagues are tackling the task with an extraordinary type of semi¬conductors called quantum dots.
These nanoscale-size crystals demonstrate the same semiconducting properties as the material from which they are “grown.” Moreover, those properties can now be applied to films thin enough to allow light to pass through. Depending on the material that is chosen and how its crystal structure is created, each dot can be tuned for sensitivity to specific wavelengths of light.
Achieving just the right mixture of elements has been a major challenge for investigators since a quantum dot contains as few as 1,000 atoms. Nevertheless, progress is being made, and Hinzer is optimistic that this approach will continue yielding the desired improvements in efficiency.
Incorporating this type of technology in low-cost concentrating systems effectively makes the system technology look very similar to traditional flat panel systems and has already earned Hinzer a Canadian Energy Innovation Award from the Ontario Centres of Excellence, an honour she shared last fall with Toronto-based company Morgan Solar Inc. The firm now markets this next generation of solar panels under the name “Sun Simba,” anticipating it will find widespread use in Ontario and elsewhere.
The SUNLab touts itself as Canada’s only university research centre investigating the Sun Simba design. At the same time, this facility also protects the patentable intellectual property it creates as well as attracts new industry partners in other collaborative projects. Together, these activities lay the foundation for new products and businesses that could return some royalties to the University. But for Hinzer, the lab’s greatest accomplishment is the talent that it nurtures.
“The best knowledge transfer to industry occurs when trained students and researchers leave the SUNLab to join emerging companies or well-established ones that are expanding in a new field,” she says. “These individuals bring with them advanced knowledge on theory, processes, fabrication, testing, supply chain and prospective clients. Some of them will even go on to form their own companies, often complementing an existing industry or increasing the strength of a specific sector.”