Pricey New Space Age Perovskite Solar Cell Aims For Low-Cost Rooftop Solar Market

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Researchers at the National Renewable Energy Laboratory and the University of Washington, have come up with a strategy for driving down the cost of solar cells while ramping up efficiency: start at the top. The team has developed a high cost, high efficiency quantum dot solar cell for space applications, where price is no obstacle. The idea is to hook the expensive new solar cell up with a cheaper — much cheaper — perovskite layer. The combined solar cell would be aimed at terrestrial applications with a more down-to-earth price point, too.

So…when will this space age research come to a rooftop near you?

Oxymoron Alert: Pricey Perovskite Solar Cells

Perovskite fans take note: in the proposed low cost solar cell, the cheap layer is not the only role for perovskite. The expensive quantum dot layer would also be made of perovskite.

Expensive perovskite is practically an oxymoron, so let’s take a closer look.

For those of you new to the topic, multijunction is fancyspeak for packing layers of different materials into one solar cell, in order to ramp up efficiency. Perovskite refers to a class of synthetic crystals that mimic the superior solar properties of the naturally occurring mineral, perovskite.

Synthetic perovskites are dirt cheap, and researchers have been making rapid progress on improving their solar conversion efficiency.

That’s where the counter-intuitive pricing strategy comes in. Colloidal quantum dot solar cell technology is costly, but the promise of high efficiency is too tempting to ignore. Here’s the explainer from NREL:

Colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties.

NREL tracks the year-by-year efficiency of various solar cells on one handy chart, and quantum dots didn’t even rate their own line until 2010:

That first quantum dot solar cell had a conversion efficiency of just 2.9% and was based on a lead sulfide formula. Things moved along quickly after that, and NREL noted a record of 12% for lead sulfide logged by the University of Toronto just last year.

NREL attributes the improvements to “better understanding of the connectivity between individual quantum dots, better overall device structures and reducing defects in quantum dots.”

The Perovskite Path To Record Solar Cell Efficiency

The NREL research team achieved its new 13.4% record for quantum dot solar cells by switching from lead sulfide to cesium lead triiodide, which is one of the perovskite versions to emerge at the front of the pack:

The latest development in quantum dot solar cells comes from a completely different quantum dot material. The new quantum dot leader is cesium lead triiodide (CsPbI3), and is within the recently emerging family of halide perovskite materials. In quantum dot form, CsPbI3 produces an exceptionally large voltage (about 1.2 volts) at open circuit.

According to NREL, the new quantum dot solar cell would be an “ideal candidate” for the topmost layer of a multijunction cell. Combined with a layer of conventional perovskite, the new cell could combine high efficiency with a price point low enough to break into the mainstream rooftop solar market.

You can get all the details in the journal Science Advances under the title “Enhanced mobility CsPbI3 quantum dot arrays for record-efficiency, high-voltage photovoltaic cells.”

What Now, NREL?

As for the real-life prospects for a high efficiency, low cost rooftop perovskite solar panel, that depends partly on the technology.

For all their promise, perovskite solar cells have a major drawback: they are fragile in real-world conditions, and the use of lead as a stabilizer makes for a questionable pathway into the sparkling green future.

Neither of those issues are un-solvable. The main issue here in the US is political will.

So far, Energy Secretary Rick Perry has been engaged in a tricky balancing act of toeing the Trump administration fossil-friendly line while continuing to promote his agency’s renewable energy programs, including the foundational research supported by NREL and other facilities in the sprawling national laboratory network.

That dance is becoming more trickier with each passing week, to the extent that Perry has also been cheering on the Trump administration’s antipathy to climate science (Perry’s track record on women’s health is a whole ‘nother can of worms).

With the Republican-lead Congress eyeballing budget cuts, chatter about President* Trump and his mental condition rising and the investigation into Russian interference coming to a head, anything could happen.

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*As of this writing.

Images: (1) “NREL scientists Joey Luther and Erin Sanehira are part of a team that has helped NREL set an efficiency record of 13.4% for a quantum dot solar cell” via NREL; (2) NREL solar efficiency chart.