Until now, solar cells have been unable to make use of the sun’s entire radiation spectrum, but this may change. An accidental discovery at the Lawrence Berkeley National Laboratory has researchers hoping that they can break the “band gap” barrier to development a new generation of photovoltaic cells with greatly increased efficiency.
Band-gap energy (BGE) is the amount of energy needed to free an electron from its atom. Existing solar cells can only capture sunlight at energies equal to or greater than their BGE. While studying the properties of light-emitting diodes, LBNL researchers discovered that the BGE of indium nitride was much lower than expected — 0.7 electron volts, instead of the anticipated 2.0.
Unlike cells currently in use, those made with indium nitride could capture low-frequency red or near-infrared light. Researchers hope to make cells from several layers of varying alloys of indium, gallium and nitrogen. They believe that it would be possible to create inexpensive two-layer solar cells with a 50% efficiency for sunlight to electricity conversion. Multi-layered cells might conceivably attain 70% efficiency. In comparison, existing cells only achieve about 33% efficiency.
