In December last year, a company called Spectrolab has achieved a new world record in solar cell efficiency. By using concentrated sunlight, Spectrolab demonstrated the ability of a photovoltaic cell to convert 40.7% of the sun's energy into electricity. By contrast, regular solar cells are 12 - 20% efficient. Multijunction solar cells are credited with helping scientists gather much more data than expected on Mars by dramatically extending the extraterrestrial lifetimes of the Spirit and Opportunity space rovers. But they were initially designed for earthbound applications. After proving themselves in space, the high-efficiency cells are finally becoming cost-effective for generating renewable energy back on Earth.Multijunction cells perform at higher efficiencies than conventional single-junction silicon solar cells, because they convert more of the solar spectrum into energy by breaking it up into chunks. For example, the first layer of Spectrolab's record-breaking triple-junction cell is composed of gallium indium phosphide, which converts short-wavelength portions of the spectrum, such as blue and UV. The second layer, made of gallium arsenide, captures the middle part of the spectrum. The third germanium layer does a good job with IR light.
"This solar cell performance is the highest efficiency level any photovoltaic device has ever achieved," said Dr. David Lillington, president of Spectrolab. "The terrestrial cell we have developed uses the same technology base as our space-based cells. So, once qualified, they can be manufactured in very high volumes with minimal impact to production flow."
The inventors of the multijunction solar cells were also recently award a $1 million prize.