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.
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.
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
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,
Enhanced Thermionic Emission.
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
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.