The current world record for triple-junction solar cell efficiency is 44 percent, but a collaboration between the U.S. Naval Research Laboratory (NRL), the Imperial College of London, and MicroLink Devices Inc. has led to a multi-junction photovoltaic cell design that could break the 50 percent conversion efficiency barrier under concentrated solar illumination.
Presently, the best examples of traditional silicon solar cells top out at around 25 percent efficiency, whereas multi-junction cells have achieved more than 40 percent. Multi-junction solar cells contain several layers of semiconducting material stacked one on top of another, each designed to absorb a different wavelength of light, thereby boosting their efficiency. On top, high band gap semiconductor material absorbs the short wavelength radiation, while longer wavelengths are absorbed by the layers below.
The key to the new multi-junction cell design was identifying what are known as "InAlAsSb quaternary alloys" as a high band gap material that can be grown lattice-matched to an indium phosphide (InP) substrate. Used in the team's multi-junction solar cell, the alloys could achieve a maximum direct band gap of 1.8 electron volts (eV), which is higher than commonly used materials that, when lattice-matched to InP, result in a maximum of 1.4 eV.
"This research has produced a novel, realistically achievable, lattice-matched, multi-junction solar cell design with the potential to break the 50 percent power conversion efficiency mark under concentrated illumination," said Robert Walters, Ph.D., NRL research physicist.
The Naval Research Lab, MicroLink, and the Rochester Institute of Technology will develop the technology over the next three years with funding from the U.S. Department of Energy (DoE) and the Advanced Research projects Agency-Energy (ARPA-E). ARPA-E projects develop technology that is promising but too early for private-sector investment.
Source: Naval Research Laboratory
In applications where space is limited or weight is crucial, such as satellites or high-flying electric relay platforms (24-7 planes) to replace communication satellites, efficiency is everything, because one needs to carry as little as possible and has to get out as much as possible.
In applications where space doesn't matter, such as powering a large home in a suburb, cost per kW rules. If the home owner only needs to cover half of his roof to make 80% of his power (and that depends on efficiency of house and appliances), then the only thing he cares about is how much cash to pay to get there.
You have a number, you aim higher, and try harder, and are happy to get there once it happens. Or lower, whatever.
The thing with solar cells is that once upon a time, "experts" said solar cells could never be made with more than "x" % efficiency. Until they realized they had not known enough to make that statement. Between making the statement and the realization, decades can pass. True for pretty much all technologies.
The silicon solar cell efficiency barrier was once thought to be around 30%. Then they started cooking up multilayer-multicompound-cells and thought it would be 40% which at some point was passed. So let's have a look at the number 50 now. It's more exciting than watching baseball!
Sure, there's no way to get close to or make more than 100%. But for theoretical considerations as of now, based on hypothetical multi-multi-super-dooper cells made from Indium Gallium Nitride, people have taken the word "seventy" into their mouths, some 10 years ago, in Berkeley, California. And then, as usually, got bashed for it by "experts".
It's a great spectacle. Get the chips, sit back and enjoy.