There's a annoying theoretical limit on the efficiency of solar cells that limits the amount of electricity they can create from sunlight. But now a team of MIT engineers has developed a system that overcomes the problem by first converting light to heat — and it could double the efficiency of solar cells. Most solar cells have to face up to the Shockley-Queisser Limit, which places a ceiling on the power-producing efficiency of a given device based on the wide spread of light frequencies that land on a surface. In the case of the most common solar cells — which are made of silicon — that limit is about 32 per cent. Some cells use multiple layers or attempt to turn absorbed heat into electricity in order to catch a few extra per cent.
But a team from MIT is thinking a little differently. The team's new device, pictured above, first absorbs heat and light from sunlight using a special layer that can re-emit radiation at specific wavelengths better suited to the nearby solar cell. That layer is made up of nanophotonic crystals, which emit specific frequencies of light when heated. By carefully tweaking the crystals to produce the correct frequency components, the device can create radiation that's more readily absorbed by the solar cell, in turn improving its efficiency. The team describes how the system works in detail in Nature Energy.
The team reckons that the system could theoretically double the efficiency of solar cells. Initial experiments using low-efficiency solar cells have demonstrated that the device can certainly improve efficiency, though there's certainly some way to go before the technique can be used commercially. First on the list is scaling the system up so that the nanophotonic layers can be made cheaply.