Designing More Efficient Solar Cells

With a climate similar to western Oregon, Germany leads the world in solar energy production. But one of the world’s leading solar cell manufacturers, SolarWorld Industries, is opening a large manufacturing plant in Oregon. That’s good news for Oregon’s economy and for a team of Oregon BEST-funded researchers who are working hard to make solar cells more efficient.

Research team members David Cohen and Steven Kevan, both from the University of Oregon, and Janet Tate, from Oregon State University, are leading a team interested in developing ways to use nanometer-sized objects to more efficiently harvest light.

The functioning of a solar cell involves two steps: absorption of sunlight to produce free charged carriers, and the transport of those carriers out of the device to serve as a source of electrical energy. The efficiency of a solar cell depends on both of these steps: how many free carriers are generated inside the device for a given amount of sunlight, and the fidelity with which the carriers are transmitted through the device and into the external world.

This Oregon BEST research project is designed to separate these steps and to optimize them independently. The researchers embed light harvesting, nanometer-sized objects in a carrier-transporting host. Because the light harvesters can be optimized for different portions of the solar spectrum, when the carriers produced in these harvesters enter the host, they will have substantial energy.

“Our primary goal is to capture this energy by a process called impact ionization, wherein the excess energy of those carriers is transformed in a concerted fashion to produce more free carriers,” says Kevan. “This is a sort of amplification or gain that is designed into the material. If all the extra carriers produced in this fashion can be collected, the efficiency of the solar cell will be correspondingly increased.”

The researchers say the key material ingredient of this approach is the junction between the harvesters and the host, so a wide range of techniques will be used to synthesize, optimize, measure, analyze, and model the interfaces in these complex, composite photovoltaic materials.

As these Oregon BEST researchers continue to improve solar cell efficiency, Oregon’s reputation as a state that invests in renewable energy research and education continues to grow, which ultimately brings new companies and jobs to Oregon.

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