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New Materials Could Boost Solar Efficiency

January 6, 2015 By Karen Henry

New materials and designs are being developed to push solar PV cells to new levels of efficiency. An article in Yale Environment 360 provides an overview of some of the more recent material advances, the impact they are having on solar PV development and the challenges that exist for their further development and widespread adoption.

Current silicon-, cadmium-telluride-, and copper-indium-gallium-selenide-based PV cells have efficiency ranges between 12 and 16 percent. Cells made from a class of minerals called perovskites, on the other hand, are becoming even more efficient. Since perovskites were first used in a solar cell in 2009, its efficiency has grown to more than 20 percent, with unconfirmed reports of efficiency levels as high as 24 percent. Such cells are easy to build and inexpensive to make, and unlike the high-heat methods for growing silicon crystals and other solar cell materials, perovskites are produced from a low-temperature liquid solution. Because perovskites can be painted onto thin, flexible substrates such as plastic, the potential applications for light, bendable and inexpensive solar panels are enormous. However, the crystals break down in humid conditions, so outdoor installations are problematic. Scientists are currently working on solutions to this problem, something they estimate could take as long as a decade.
Another technology that is being developed is a high-performance cell with multiple semiconductor layers. Each layer is “tuned” to absorb different light wavelengths. By splitting the solar spectrum into separate colors, the cells maximize the harvest for each. Two junction cells made with gallium-arsenide have already achieved 30 percent efficiency, and researchers anticipate this could reach 50 percent. Gallium-arsenide is able to absorb a thousand times more strongly than silicon and can be extremely thin. However, the material is expensive, and adding the layers is complicated and costly.

Still another design uses nanometer-sized crystals called quantum dots that are able to confine energized electrons and help them knock loose others, a process that can potentially recover a third of light energy normally lost as heat. While scientists have only achieved 8.6 percent efficiency with this material, a single layer could theoretically achieve 45 percent efficiency.

Advances like these could herald in a new era of solar technology, but they will not be broadly developed or become commercialized unless companies invest in them. Stronger, more consistent energy policies are also needed, the article concludes.

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