But this cell hasn’t bested any records yet. Its efficiency was about 6 percent in tests, so it has a long way to go before it can compete against existing silicon solar cells, let alone show up on a rooftop. But this work was only meant as a proof of concept of exciton fission in a solar cell. To bump the cell’s efficiency higher, Baldo says, will require some engineering work to optimize it for exciton fission.In this sense, what the MIT team demonstrated wasn’t so much a competitive technology but a new tack for going beyond the limits of existing photovoltaics, says Joseph Berry, a senior scientist at the National Renewable Energy Laboratory. “What’s cool here is that this is a fundamentally different approach from traditional photovoltaics,” he says. “It’s an idea that’s been around for a long time, but hadn’t been translated into any kind of functional device.”Berry and his colleagues at NREL are exploring other ways of advancing solar cell efficiency without the added complexity and cost of multi-junction cells. One of the most promising directions being explored by Berry are perovskite cells , which use synthetic materials that have structural properties similar to the naturally occurring mineral Perovskite. The first perovskite solar cells were only produced a decade ago, but since then they have witnessed the fastest efficiency gains of any type of solar cell to date.Perovskite cells have a number of advantages over traditional silicon solar cells, says Berry, in particular their tolerance for material defects. Just a few unwanted particles on a silicon solar cell can render it useless, but perovskite materials still function well even if they’re not perfect. They also handle photonic energy more efficiently than silicon. Indeed, one of the main reasons silicon has dominated solar cell technology is not because it’s the best material for the job, but simply because scientists know so much about it due to its widespread use in digital technologies.
So far, none of these next-generation solar cells have found their way into commercial products. Almost all of the solar panels currently in operation are using traditional single-layer silicon cells, which have been proven to withstand the elements for decades. Getting perovskite-based solar panels into the field will require demonstrating that they’re stable and can last for 20 or more years. Berry says a number of companies have already deployed small-scale perovskite panels, which he hopes will pave the way for wider adoption down the road.
Looking to the future, Berry says it’s conceivable that the exciton fission technology under development at MIT could be combined with perovskite solar cells to increase their efficiency. “It’s not an either/or proposition,” Berry says, but first exciton fission must prove that it’s efficient enough for real-world applications. Ultimately, getting more sunlight on the grid will likely involve a suite of solar technologies, each with its own advantages.
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These combination or “multi-junction” cells have already hit efficiencies above 40 percent—twice that of a traditional solar panel on the market today.“The most important thing to getting this technology to the market is being very open to unique use cases,” says Paul Meissner, CEO of Silicon Valley-based startup Energy Everywhere, one of a handful of new companies trying to develop perovskite, along with other unproven technologies.