Hybrid Solar Cells Using Mismatched Materials Are Hard to Produce but Potentially More Efficient

Hybrid solar cells based on mixing mismatched elements can enhance efficiency of solar cells according to researchers from the University of Michigan and Tyndall National Institute in Ireland. They have discovered new materials that could give birth to a new breed of highly efficient solar cells.

The research team, led by Rachel Goldman of the University of Michigan, is currently developing a unique class of materials called highly mismatched alloys to greatly enhance the efficiency of solar cells. They claimed that these materials can fully capture the sun’s rays, unlike traditional solar cells.Conventional solar cells convert radiant energy from the sun into electricity by absorbing light. However, the sun gives out light at different wavelengths, each with different intensities of energy, and current solar cells only respond well to some wavelengths.

The cells only harness energy from the visible spectrum, holding 43 percent of the sun’s radiant energy. But the infrared portion of the range, which offers about 52 percent of solar energy, is often overlooked in solar panel production.

The most efficient solar cells are made of multiple materials that can capture a greater portion of the sunlight spectrum, and solar panel developers worldwide are seeking to develop the perfect solar cell that will make use of the sun’s infrared light.

The research team was very interested in using highly mismatched alloys for solar cells because its electrical and optical properties drastically change when exposed to certain elements.

In their experiments, the researchers made samples of gallium arsenide nitride, a highly mismatched alloy with nitrogen, to tap into the infrared radiation.

One of the biggest problems to get mismatched alloys out of the lab is that the materials do not naturally mix together with the elements that imbue them with special properties. However, the researchers used molecular beam epitaxy, which involves vaporizing pure samples of the mismatched elements and combining them in a vacuum, to coax the nitrogen to mix with their other elements.

If researchers can learn to control the formation of these clusters, they could build hybrid solar cells that are more efficient at converting light and heat into electricity, Ms. Goldman said.

A large amount of efficiency is possible if future solar panels could capture energy directly from the sun and indirectly from energy re-radiated all around by the ground and buildings.

"The availability of higher efficiency thermoelectrics would make it more practical to generate electricity from waste heat such as that produced in power plants and car engines," Ms. Goldman added.

The team’s research in hybrid solar cells is funded by the National Science Foundation, the Science Foundation Ireland and the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center financed by the United States Department of Energy.

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