New Materials Make Photovoltaics Better  

Technology Review has a look at improvements in solar PV materials science - New Materials Make Photovoltaics Better.

A startup called Solar Junction says its pilot manufacturing plant is producing solar cells units that are more efficient than the best ones on the market today. The advance, based on new semiconductor materials that the company has developed, could help make a type of solar power system called concentrated photovoltaics a far more attractive way to generate electricity from the sun.

Concentrated photovoltaic systems account for a small fraction of total solar power today—with only several megawatts of production capacity installed, compared to many gigawatts of capacity for conventional solar panels. They're limited to very sunny areas, where they compete with solar thermal, the cheapest form of solar power today, which uses mirrors to concentrate sunlight for the purpose of generating steam for steam turbines. Advances in solar cell efficiency have only recently made concentrated photovoltaic systems economical in some areas.

Craig Stauffer, cofounder of Solar Junction, based in San Jose, California, says his company's new cells could bring the price of solar power to below 10 cents per kilowatt hour, compared to 16.5 cents per kilowatt hour or more for typical solar panels. Solar Junction's cells require fewer layers than many other ultra-efficient solar cells and are better matched to the solar spectrum.

Solar Junction's cells are designed for photovoltaic systems that use mirrors or lenses to concentrate sunlight 1,000 times. Concentrating sunlight improves the efficiency of most solar cells, but solar cells designed for use under such high concentrations—called multi-junction cells--do particularly well because they incorporate two or three semiconductor layers for absorbing different colors of sunlight, rather than the single semiconductor layer used in conventional solar panels.

Concentrated solar power has been held back by the difficulty of finding semiconductors that divide up the spectrum in the optimal way, but that also have matching crystalline structures, which makes the cells easy to fabricate. Solar Junction's technology tackles the problem for the infrared end of the spectrum, the part that's proven the most challenging for multi-junction cell developers. In conventional multi-junction cells semiconductor materials designed for this part of the spectrum either absorb light that's too far into the infrared or aren't compatible with the other semiconductors in the cell, and so require costly buffer layers.