Although photovoltaics have seen marked advances in recent years, they are still remarkably inefficient when it comes to harvesting the energy they receive. Even the best production silicon photovoltaics convert less than 20 percent of the light they receive to electricity.

Silicon photovoltaics suffer a compound problem in energy generation. First, they can only capture a narrow spectrum of the sunlight they receive, producing immediate waste energy from the unused light in the form of heat. Second, silicon photovoltaic efficiency suffers from heat. In essence, a cell's own waste energy cripples it. Silicon photovoltaics produce zero energy at temperatures even below 100 degrees Celsius, regardless of how much light they receive.

Rather than trying to improve the efficiency of these already self-hobbled solar cells, Stanford researchers, led by materials sciences and engineering assistant professor Nick Melosh, have created a new material that can harvest both incident light and heat energies. Their paper has been published in the August 1st edition of Nature Materials online.

To create a solar cell that would flourish under both light and heat, they broke away from the familiar silicon semiconductor platform and instead looked to gallium-based photovoltaic surfaces. But in order to harvest the heat generated by the waste energy, they needed to add an additional layer of material, for which they used a thin coating of cesium metal. They have dubbed the energy harvesting process PETE, for Photon Enhanced Thermionic Emission.

Unlike traditional silicon cells, Melosh's group's don't hit their peak efficiency until temperatures in excess of 200 degree Celsius--well above the point where silicon cells have already been rendered inert. To make the best use of the material's properties, they could be used in solar concentrators, where temperatures regularly exceed 800 degrees Celsius. Further waste heat could then be used in thermal exchangers, much in the same way solar heat is currently harvested to create energy.

Melosh's team is looking to hit 50 to 60 percent conversion between the cesium layer and semiconductors like gallium arsenide. And to make the material and process even more promising, fabrication costs for a standard six inch wafer of the material put it theoretically on par with oil-based energy generation by output.