Consortium Achieves Record-High Solar Cell Efficiency and Closes in on The 50% Efficiency Mark

Using a novel technology that adds multiple innovations to a very high-performance crystalline silicon solar cell platform, a consortium led by the University of Delaware has achieved a record-breaking combined solar cell efficiency of 42.8 percent from sunlight at standard terrestrial conditions.

That number is a significant advance from the current record of 40.7 percent announced in December and demonstrates an important milestone on the path to the 50 percent efficiency goal set by the Defense Advanced Research Projects Agency (DARPA). In November 2005, the UD-led consortium received approximately $13 million in funding for the initial phases of the DARPA Very High Efficiency Solar Cell (VHESC) program to develop affordable portable solar cell battery chargers.

Combined with the demonstrated efficiency performance of the very high efficiency solar cells’ spectral splitting optics, which is more than 93 percent, these recent results put the pieces in place for a solar cell module with a net efficiency 30 percent greater than any previous module efficiency and twice the efficiency of state-of-the-art silicon solar cell modules.

As a result of the consortium’s technical performance, DARPA is initiating the next phase of the program by funding the newly formed DuPont-University of Delaware VHESC Consortium to transition the lab-scale work to an engineering and manufacturing prototype model. This three-year effort could be worth as much as $100 million, including industry cost-share.

The ground-breaking research was led by Allen Barnett, principal investigator and UD professor of electrical and computer engineering, and Christiana Honsberg, co-principal investigator and associate professor of electrical and computer engineering. The two direct the University’s High Performance Solar Power Program and will continue working to achieve 50 percent efficiency, a benchmark that when reached would mean a doubling of the efficiency of terrestrial solar cells based around a silicon platform within a 50-month span.

“The University of Delaware is very proud of the achievements of Allen Barnett and Christiana Honsberg, both their research and their work in leading the consortium,” UD President Patrick T. Harker said. “We are grateful to DARPA for its confidence in the University and very much look forward to working with DuPont and our other partners in industry, government and academia on this project, which will have wide application and will be of particular benefit to our men and women in the service.”

“UD has become an important center for renewable energy research, and we applaud the efforts of the University-led consortium,” UD Provost Dan Rich said. “This project is of vital importance, particularly given the pressing need for alternative sources of energy.”

"The University is committed to the advancement of leading-edge research that solves important problems and results in the invention of new technologies aimed at enhancing society," Carolyn Thoroughgood, vice provost for research and graduate studies at UD, said. "This project highlights the quality of research at UD and also demonstrates the value of collaboration."

“The achievement of this benchmark is a major step forward in the ongoing development of low-cost solar photovoltaic technology,” Rhone Resch, president of the Solar Energy Industries Association, said. “Furthermore, we applaud DARPA for making a strategic investment in American’s energy security. We anticipate that this project will result in a wide range of commercial solar applications that will benefit the U.S. military and American consumers alike.”

"Many of us have been working with programs to take us to a real photovoltaic energy future. This project is already working in that future. DARPA has leapfrogged the 'conventional,' demonstrating that creativity and focus can significantly accelerate revolutionary research-bench concepts toward reality, demonstrating this does not have to take decades,” Lawrence L. Kazmerski, director of the U.S. Department of Energy’s National Center for Photovoltaics at the National Renewable Energy Laboratory in Golden, Colo., said. “This is a first step—but a significant one in making sure our energy future is what we know it should look like."

The consortium’s goal is to create solar cells that operate at 50 percent in production, Barnett said. With the fresh funding and cooperative efforts of the DuPont-UD consortium, he said it is expected new high efficiency solar cells could be in production by 2010.

The highly efficient VHESC solar cell uses a novel lateral optical concentrating system that splits solar light into three different energy bins of high, medium and low, and directs them onto cells of various light sensitive materials to cover the solar spectrum. The system delivers variable concentrations to the different solar cell elements. The concentrator is stationary with a wide acceptance angle optical system that captures large amounts of light and eliminates the need for complicated tracking devices.

The VHESC would have immediate application in the high-technology military, which increasingly relies upon a variety of electronics for individual soldiers and the equipment that supports them. As well, it is hoped the solar cells will have a large number of commercial applications.

Today, the American soldier carries a pack that weighs nearly 100 pounds of which about 20 pounds are the three-day supply of batteries needed to power their gear. The DARPA program aims to dramatically reduce the battery logistics pipeline and provide the soldier with more power at reduced weight, thus improving mobility, survivability and the availability of advanced electronic technologies on the battlefield. With the dramatically higher efficiency of the VHESC technology, solar rechargers could be integrated into common battlefield devices such as night vision goggles, radios and GPS navigation systems.

Barnett and Honsberg said that reaching the 42.8 percent mark is a significant advance in solar cell efficiency, particularly given the unique small and portable architecture being used by the consortium and the short time – 21 months – in which it was developed.

Modern solar cell systems rely on the concentration of the sun’s rays, a concept similar to youngsters using magnifying glasses to set scraps of paper on fire. Honsberg said the previous best of 40.7 percent efficiency was achieved with a high concentration device that requires sophisticated tracking optics and features a concentrating lens the size of a table and more than 30 centimeters, or about 1 foot, thick.

The UD consortium’s devices are potentially far thinner at less than 1 centimeter. “This is a major step toward our goal of 50 percent efficiency,” Barnett said. “The percentage is a record under any circumstance, but it’s particularly noteworthy because it’s at low concentration, approximately 20 times magnification. The low profile and lack of moving parts translates into portability, which means these devices easily could go on a laptop computer or a rooftop.”

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