Clean Power perovskite solar cell via EPFL

Published on February 5th, 2016 | by Tina Casey

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Yes, Solar Can Go Lower (Perovskite Solar Cells, That Is)

February 5th, 2016 by  

Some solar industry observers have predicted that the cost of solar power will not continue to drop at its current rapid pace, but it’s still going to keep dropping, and with that in mind let’s take a look at a new breakthrough from EPFL, Switzerland’s Ecole Polytechnique Fédérale de Lausanne. It has concocted a perovskite solar cell that replaces a critical — but pricey — layer with a new material at only one-fifth the cost.

perovskite solar cell via EPFL

The Perovskite Solar Cell Bottleneck

For those of you new to the topic, perovskites are a class of synthetic crystal-ish minerals that share the structure and solar-friendly properties of naturally occurring perovskite. Perovskites are relatively cheap and easy to synthesize, and they have been drawing the attention of solar cell researchers around the world.

To ice the cake, perovskite solar cells can be manufactured in the form of a film, through relatively inexpensive solution-process methods.

Recent progress in the perovskite solar cell field has yielded certified power conversion efficiencies topping 20 percent, which is not quite up there with the best silicon solar cells but still a nifty tradeoff for the relatively low cost.

The cost of perovskite solar cells could go even lower without losing efficiency, except for a “bottleneck” consisting of the expensive materials used to form the hole-transporting layer of the solar cell (that’s the layer that receives positive charges from sunlight and passes them along).

A New Material For Perovskite Solar Cells

According to the EPFL, currently the best-performing perovskite solar cells have been made with materials that top €300 per gram to manufacture, a prohibitive price point in terms of commercial development.

The researchers came up with a low cost, alternate layer that seems to have outperformed their expectations. Instead of simply replacing the expensive layer without a loss of efficiency, the new layer resulted in a measurable improvement over solar cells made with the more expensive layer.

Here’s the rundown from the abstract:

In this work, we present a molecularly engineered hole-transport material with a simple dissymmetric fluorene–dithiophene (FDT) core substituted by N,N-di-p-methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for a family of potentially low-cost hole-transport materials. We use FDT on state-of-the-art devices and achieve power conversion efficiencies of 20.2% which compare favourably with control devices with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). Thus, this new hole transporter has the potential to replace spiro-OMeTAD.

Got all that? For more details you can check out the full article, just published in the journal Nature Energy under the title, “A molecularly engineered hole-transporting material for efficient perovskite solar cells.

About Those Perovskite Solar Cells

We had an interesting discussion about perovskite solar cells last summer during a visit to EPFL, where we had a chance to sit down with the world renowned thin film solar expert Michael Graetzel.

Part of the discussion revolved around the use of a toxic material — lead — in perovskite solar cells. Lead is used in perovskite solar cells as a stabilizer, and until a substitute for lead comes up, Graetzel’s prediction is that lead-based perovskite solar cells would be limited to situations where cradle-to-grave tracking could ensure that lead from the solar cells would not enter the environment at any point during their lifespan.

Clean tech or not, materials lifecycle is critical issue for solar cells. Lead in particular is a touchy subject here in the US, where we’ve gotten a chilling reminder about lead hazards from the ongoing crisis in Flint, Michigan due to the potentially criminal mismanagement of the city’s water supply.

Speaking of lifecycle issues shadowing the clean tech field, get a load of this:

soil bacterium via U Wisc

Gross, right? That’s actually not the problem. That’s a common, beneficial bacterium called Shewanella oneidensis. As described by researchers at the University of Wisconsin-Madison this little guy lives in the soil, where it converts metal ions to iron and other metals, which in turn are used as tasty snacks by other microorganisms.

The problem is that the compound nickel manganese cobalt oxide, which is apparently emerging as the material of choice for use as a catalyst in lithium-ion batteries, is toxic to Shewanella oneidensis.

One obvious solution is to keep such batteries out of landfills, but as the crisis in Flint demonstrates, the human factor can come into play with devastating results.

So far the researchers are treating the results of their bacterium study as a possible “red flag” that underscores the need to develop clean tech that is clean throughout its lifecycle.

That leads us all the way back around to perovskite solar cells. About two years ago we noticed that researchers were developing perovskite solar cells that deploy tin instead of lead.

We’re also curious to see how the cutting edge field of “hot-carrier” technology could influence the design and materials used in perovskite solar cells.

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Images: Top, “3-D illustration of FDT molecules on a surface of perovskite crystals” by Sven M. Hein (copyright EPFL); bottom, Shewanella oneidensis by Ella Marushchenko/University of Minnesota via University of Wisconsin-Madison.


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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



  • Shane 2

    Maybe a plastic or glass coating transparent to most of the sunlight spectrum could be used to prevent water from destroying the perovskite.

  • JamesWimberley

    The Gizmag report on the FDT innovation (link) comments that it offers hope of greater stability as well as lower cost:

    “While no determination has yet been made on the stability of the compound used in the study, two considerations leave room for optimism. First, the inorganic nature of the compound is expected to make it more resistant to weather and biodegradation. And secondly, the FTD core material can be reportedly modified with ease, creating not one, but a family of compounds.”

    There is no reason to give up just yet on perovskite stability, or to be cynical about the widespread efforts to find a solution.

    • MtnMark

      I’m not giving up. I have hope for perovskites. There is a lot of good work being done on it right now. I think commercialization is at least a few years away.

  • andereandre

    Grrrrrr.

  • Otis11

    Overly politicized and missed the actual issue with perovskites.

    Come on Tina…

    • Darin

      There’s an underline but was it supposed to be a link. Otherwise, what is this issue you are referring to?

      • Otis11

        The issue with perovskite solar is durability/longevity… And it’s a notable issue, but the article completely over looks that and focuses other “issues” that aren’t really much of a problem.

        And it’s highly politicized when there’s no reason to be…

  • Roger Lambert

    What?!?

    Landfills must represent 0.0000000001 percent of land area. And we are worrying about possible leaching of physically-sequestered lead or nickel manganese cobalt oxide out of solar cells or Li-On batteries that might possibly be manufactured someday which might someday make it into a landfill, and which might someday somehow occur in a high enough concentration to possibly hurt some bacteria or people which might be present in a local area around that 0.00000000001 percent of land area?!?

    I suppose we are just supposed to forget that it is the dose that makes the poison?!?

    Who comes up with such a paranoid concern about solar cell research? Surely not someone with ties to the fossil fuel industry?

    Why does this “issue” take up up fully one-half of an article about perovskite crystals?

    I thought the big drawback of perovskite crystals was a short working lifespan compared to standard panels. But that, unfortunately did not seem to be addressed here.

    • What harm could it do?

      hmm, .000000001 %, how big was love canal and how many people/large of an area did that impact? how about PFOA’s in NY, lead in flint, nuclear byproducts here, arsenic there, a dose of tritium there, PCBs down half of the Hudson. how many Superfund sites are there? brown fields? dry cleaners that illegally dumped stuff? You are correct, landfills make a small percentage of space, but the harm spreads out and compounds with other harms that have already been done.

      • Shane 2

        Mandate the formation of battery collection points. Make the sending of batteries to landfill illegal. Have appropriate penalties and law enforcement. Have a payment for large battery packs such as those in cars so that there is a clear economic incentive to have the battery packs go to recycling. Pay snitches who inform on people breaking the law.

      • Roger Lambert

        I think you are having an analogy problem here. The “harm” is supposedly to a microbe that lives everywhere in the world, not just under dumps.

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