Perovskites for "Tandem" Solar Cells

"Tandem" photovoltaics that may give a boost to traditional silicon solar cells

2 min read
Perovskites for "Tandem" Solar Cells
Rongrong Cheacharoen/Stanford University

By developing a way to coat silicon photovoltaics with crystals known as perovskites, researchers are creating tandem solar cells that may be substantially better at converting light to electricity than conventional solar cells while also being manufactured at low cost.

Although photovoltaics based on crystalline silicon currently account for 90 percent of the global photovoltaic market, the power conversion efficiency of silicon photovoltaics has been at a creep, advancing from 25 percent to 25.6 percent in the past 15 years. In order to produce solar cells with higher efficiencies while making the most of the existing manufacturing capacity for silicon photovoltaics, the industry has explored devices that combine silicon with other materials. But these so-called tandem solar cells, despite offering better efficiencies, have have yet to capture more than a fraction of a percent of the global photovoltaic market. Why? Because they are typically made using expensive processes.

Scientists at MIT and Stanford, hoping to achieve high efficiency without high costs, looked into creating tandem solar cells using perovskites, which have recently become the darlings of the photovoltaic world. The efficiencies of solar cells made from perovskites have shot up from under 4 percent to more than 20 percent in the last five years or so, quickly catching up to silicon. Moreover, perovskites are inexpensive and easily produced in labs. The MIT-Stanford group detailed its findings in today’s online edition of the journal Applied Physics Letters.

In the new tandem solar cells, a layer of methylammonium-lead(II)-iodide perovskite is stacked on top of crystalline silicon. The device also incorporates layers of other materials on top of and between the perovskite and silicon to assist with the flow of electric charge. The perovskite absorbs higher-energy visible photons, while the silicon absorbs lower-energy infrared photons. According to the researchers, dividing the spectrum of sunlight between specialized absorbing layers is more efficient than letting a single layer attempt to convert the entire spectrum by itself.

The team says it developed a 1-square-centimeter tandem solar cell with a 13.7 percent conversion efficiency. The scientists suggest that if they could improve each component of the tandem solar cell to match the highest-quality devices available today, they could achieve an efficiency of roughly 29 percent; ultimately, they predict, perovskite-silicon tandems could surpass 35 percent efficiency.

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Practical Power Beaming Gets Real

A century later, Nikola Tesla’s dream comes true

8 min read
This nighttime outdoor image, with city lights in the background, shows a narrow beam of light shining on a circular receiver that is positioned on the top of a pole.

A power-beaming system developed by PowerLight Technologies conveyed hundreds of watts of power during a 2019 demonstration at the Port of Seattle.

PowerLight Technologies
Yellow

Wires have a lot going for them when it comes to moving electric power around, but they have their drawbacks too. Who, after all, hasn’t tired of having to plug in and unplug their phone and other rechargeable gizmos? It’s a nuisance.

Wires also challenge electric utilities: These companies must take pains to boost the voltage they apply to their transmission cables to very high values to avoid dissipating most of the power along the way. And when it comes to powering public transportation, including electric trains and trams, wires need to be used in tandem with rolling or sliding contacts, which are troublesome to maintain, can spark, and in some settings will generate problematic contaminants.

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