Rays of Hope

Profs poised to make solar energy more affordable

Throughout the world, environmental, economic, and political events seem to be aligning with the stars—most notably the solar system's largest star—to create unprecedented urgency for new, cost-effective, "green" power. Arguably, there has never before been a time when the mission to find cost-effective ways to harness the sun's energy has seemed more environmentally necessary or more economically and politically expedient than it is today.

Global concerns about the effects on climate of fossil fuel-generated greenhouse gases combined with budget-busting gasoline and fuel-oil prices gave rise to then-Senator Barack Obama's campaign proposal to increase federal spending for clean-energy research, development, and deployment to $150 billion over 10 years.

At Purdue, leaders for the university's Solar Energy Research Group in the School of Chemical Engineering, Rakesh Agrawal and Hugh Hillhouse, say they hope that all these factors will result in robust funding for their future solar energy research from the National Science Foundation. They hope to expand their ongoing research aimed at creating an economical means of producing electricity from the sun and training the next generation of students for a solar economy of the future.

Agrawal, the Winthrop E. Stone Distinguished Professor of Chemical Engineering, says not only is now an opportune time in history to pursue solar energy answers, but that science is ready to conquer the challenges that stand in the way of making solar solutions affordable.

Agrawal with his equipment

"Never in my life has it been better than this," Agrawal says. "These are exciting times because I think there is a need and I think scientifically and technically we have advanced enough that there are possibilities of solutions. The dream I have is to bring chemical engineering principles to bear on our problems in order to make things in large quantities, such as nanocrystalline inks (to be used in solar cells), at a very low cost."

Agrawal and Hillhouse oversee a team of graduate and undergraduate researchers that is developing novel processes and unique nanostructures to create thin-film photovoltaic devices, or solar cells. Solar cells generate electricity directly from visible light by means of the photovoltaic effect. These thin-film devices hold the promise to become a cost-effective alternative to today's crystalline silicon-based devices; the electricity produced using silicon-based devices costs about three times more than electricity produced using fossil fuels.

The thin-film photovoltaics use nanocrystals created by solution-based chemistry in order to avoid the inefficient, energy-intensive vacuum co-evaporation method that is common in creating current solar cells.

"The cost of turning sunlight into electricity is too high right now; that's the big problem," says Hillhouse, associate professor of chemical engineering. "The cost lies in the chemical and material processing. And because chemical engineers have a long and distinguished history of figuring out ways to scale things up and produce things in more cost-effective ways, it is a great opportunity."

Hillhouse and Agrawal hope to secure funding for an ambitious multidisciplinary, multi-institutional research effort to "enable a fossil-fuel-free world" and educational initiatives to train "a new breed of experts" that can identify and solve the grand challenges of a future solar economy.

Their educational goal is to instruct future researchers, teachers, leaders, and entrepreneurs so they have an "interdisciplinary, systems-level understanding of the complexities and constraints" of the evolving energy economy and they understand the art of sun-to-electricity and sun-to-liquid-fuel solutions. The researchers also intend to develop and deploy new educational materials and models on the Web in order to make a broad educational impact.

The research will use systems analysis to create a system model of an optimized solar economy in which all interactions and opportunities are revealed. In addition, the researchers intend to develop new concepts for capturing, converting, and storing solar energy that will yield cost-effective manufacturing processes. Those processes will reduce the cost of electricity from solar cells and increase the efficiency of solar-energy harvesting and conversion to liquid fuels.

A potentially revolutionary approach In addition to the collaborative research Hillhouse and Agrawal conduct, Hillhouse is working with post-doctoral assistants, graduate students, and undergraduates to develop prototype solar cells based on nanotechnology that he and his team patented in 2006. The technology, purchased from Purdue by investors, gave birth to NanoG, a corporation for which Hillhouse serves as chief scientific advisor.

The patent is on a new fabrication technology used to form a nonconventional solar cell that Hillhouse says holds the potential to revolutionize solar energy by making it far less expensive to harness.

"We've come up with a way to grow and template interconnected wires that are smaller in diameter than anybody's ever made before—about four nanometers in diameter," Hillhouse explains. "This invention—the capacity to make coatings composed of a network of unique and special nanoscopic wires—is a key step in the development of a new generation of higher efficiency solar cells that may dramatically reduce the cost of electricity from sunlight."

The structures actually form spontaneously in seconds when conditions are right—they self-assemble, Hillhouse says. "This quick and easy process has the potential to be very inexpensive," he says. "Currently, we're focused on making a prototype solar cell that is more efficient, such that it merits commercial-scale production and can justify large-scale investment. We are hoping to have a prototype within a year."

Hillhouse proudly points to the students who have helped him every step of the way: "NanoG is something that has only come after a lot of hard work and a lot of student involvement. There are at least three PhD students who share rights on the invention. All the students who work with me are intellectual partners in every sense of the word. The investors bought the patent from Purdue, and the students who worked on the project got a check."

-Amy Raley