Coal-Killing Perovskite Solar Cell Beats 20% Efficiency Mark, Aims For 30%

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The lab of perovskite solar cell pioneer Michael Graetzel is at it again. The Switzerland-based research team has  been fine-tuning its method for growing the finicky crystals on a thin film, and the latest variation injects a “burst” of vacuum flash into the mix. If commercialized, the new technique could lower manufacturing costs, and keep the cost of solar power heading on a downward spiral.

perovskite solar cell Graetzel

The Coal-Killing Perovskite Solar Cell

When presumptive Democratic nominee Hillary Clinton said that “we’re” going to put coal miners and mining companies out of business earlier this year, she most likely did not mean that Professor Graetzel and his team would be directly responsible for the death of coal. However, solar-to-electricity technology has been rapidly marching past the limits of coal-to-electricity technology, and the perovskite field is a good example.

For those of you new to the topic, perovskite crystals are relatively easy to manufacture, and they are much cheaper than silicon.

Solar researchers began tinkering with perovskites in earnest less than ten years ago. From a starting point of less than 4% solar conversion efficiency in 2009, research teams around the globe have quickly teased the rate up into the double digits while steadily pushing down costs.

Recipe For A Low Cost Solar Cell

The basic technique for creating perovskite solar cells is to ‘grow’ the crystals on a thin film. The challenge is to make that layer as uniform as possible, while making each grain of crystal approach a relatively large size.

It’s a complicated dance that involves spraying a solution of raw materials onto conductive glass and applying heat. The crystals form as the solution dries.

Graetzel’s team has found that the process can be manipulated to create a more uniform layer. One technique involves spinning off excess moisture, literally by spinning the glass while the solution is drying:

solar cell efficiency perovskite 2

The new vacuum flash technique provides a twofer. If you’re feeling ambitious, you can look it up in the journal Science under the title, “A versatile vacuum-flash assisted solution process for high-efficiency large-area perovskite solar cells.”

For those of you on the go, vacuum flash refers to the vaporization that occurs when a heated liquid is briefly exposed to a vacuum:

solar cell effciency perovskite 1

Graetzel’s team found that the process is ideal for removing volatile compounds in the excess liquid, helping to ensure that the resulting film grows uniformly. The ‘seeds’ left behind also tend to produce high quality crystals, which boosts conversion efficiency.

According to the lab, the conversion efficiency reached through the new fabrication method topped out at more than 20%.

Aside from tweaking the fabrication process, Graetzel’s lab has also been addressing the cost of materials used in the solution for growing perovskite crystals. Last January, for example, the lab announced that it had found a replacement for one such material, yielding the same conversion efficiency at one-fifth the cost.

More Life For Silicon Solar Cells

Perovskite solar cells offer another pathway for transitioning out of coal, but it’s too soon to sound the death knell for silicon.

One main obstacle is the lead component in conventional perovskite solar cells. In a conversation with CleanTechnica a couple of years ago, Graetzel cautioned that the commercial use of perovskite solar cells could be limited to secure sites where cradle-to-grave materials management can virtually eliminate the risk of lead hazards.

Assuming the lead issue can be resolved, Graetzel foresees that a combination solar cell with perovskites layered onto silicon could jump over the 30% efficiency mark. Such a solar cell would be considerably cheaper than silicon alone.

In that case, rather than killing off silicon solar cells, perovskites could actually extend the lifespan of the silicon industry — at least until something cheaper comes along.

Photo (cropped): via EPFL (École polytechnique fédérale de Lausanne), other images are screenshots.

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Tina Casey

Tina specializes in advanced energy technology, military sustainability, emerging materials, biofuels, ESG and related policy and political matters. Views expressed are her own. Follow her on LinkedIn, Threads, or Bluesky.

Tina Casey has 3138 posts and counting. See all posts by Tina Casey

31 thoughts on “Coal-Killing Perovskite Solar Cell Beats 20% Efficiency Mark, Aims For 30%

  • Lower air pressure means a lower boiling point, which may enable a faster, less energy intensive production process.

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  • The report in PVmagazine claims the efficiency was 19.6%. Not that it matters. For tandem cells, the efficiency of the perovskite layer is already high enough to make the concept very attractive. The issues remain durability and low – cost fabrication. Grätzel is making progress on both.

  • This could give a double junction cell, silicon and perovskite, approaching 30% at a low cost. We need to get to 30%. The future is looking very good.

    • Solar is already competitive in many places, so need is maybe an exageration, but it sure could make for a fearsome competitor if the price and longevity are there.

      • Nope it is not an exaggeration. Solar is driving cost down fast but so is wind power and the worlds first osmotic power plant in conjunction with geothermal targets $0.0136/kWh and is owned and initiated by a guy who owns 20% of SMA that is the leader in solar inverters.

        Solar has a big problem with annual shifts and diurnal power output shifts, which is troublesome. Wind has far less power output shifts and osmotic power is baseload that quite easily and relatively low cost could be on demand power.

        In so far solar is twice as expensive as wind and five times as expensive osmotic power provided that the development targets are met.

        Solar needs to drop prices fast to stay competitive. Currently solar enjoys the fact that the penetration is very small and that solar coincide with the diurnal demand curve but once the high margin peak demand part is saturated solar has to aim for a much lower cost point, which is clearly understood in the business that is constantly improving on all metrics.

        • Dropping to 1/10 it’s current cost would be great, but there are still a lot of area where the current price works.

          • Even if panels achieved that there are other cost involved so 90% LCOE cost drop is probably a stretch for utility scale solar.

            For roof solar it might be possible if you have to redo roofing and can substitute roofing with solar panels or if you integrate solar panels as roofing in the first place.

            If pricing for health, property and climate damage was factored into fossil fuels or if just the other subsidies was lifted solar more or less fits in everywhere.

            As it is now subsidies for solar and wind are being phased out while fossil fuels and nuclear get to keep their much costlier subsidies

        • Have you a link to a positive osmotic power story? Google only dug up dismissive articles.

          • Cant say I have Statkraft in Norway has made a prototype plant but only operate with the osmotic gradient between freshwater and seawater. The salinity in the new osmotic power plant under construction is 16% and the osmotic gradient is high because they use brackish water with about 1,8% salinity.

            I know Peter Holme, CEO and founder of Aquaporin very well and also his CTO Oliver Geschke because I tried to hire him once. They have a highly permeable membrane technology that retains salt very efficiently and they did some succesful testing with Statkraft.

            The membranes in the Danfoss project are 100% standard off the shelf products designed for the reverse osmotic freshwater business and the chosen supplier is Japanese.

            Osmotic power works in theory as well as in practice but is only economical when you have a sufficient gradient and part of the pumping is done anyway because you connect to a geothermal installation.

          • Early tests had negative results because the membrane clagged up with microscopic marine life. So I can’t see it working as a generation process, but perhaps as a storage process, where you have complete control over the saline solution.

          • I simply refuse to believe they do not totally dominate this problem today because it 100% identical to the problems faced by the reverse osmotic industry. A friend of mine supplies small deployable reverse osmotic plants mainly for aid projects and military customers. I can ask him about the problem. I also think you are quite good at this in the states because I seem to remember that Phoenix and Vegas use it for water supply. Anyway pumping and filtering are speciality expertise in Denmark so I cannot imagine that as a serious showstopper.

  • No mention of how much silver it would use.

    • Perhaps because it’s unimportant? There is no shortage of silver, IIRC the price isn’t going up, and PV manufacturers and suppliers are working on cheaper copper conductors.

      • Silver is $560/kg.

        Copper is $10/kg.

        I suppose if there is a program to recycle old solar panels and catalytic converters, then it is ok.

    • Well, every solar panel is back coated with silver to reflect light back through the cells, probably around 100 nanometers thick. It doesn’t come to much per square meter.

      • Ronald, the silver is used as a charge collector, not as a reflector.

        • It can both reflect light and return electrons to the silicon. If reflection wasn’t important I think they’d skip applying silver and just increase the aluminium paste wiring they print on the back.

          • If conductivity and conductivity of it’s oxidation products wasn’t the reason for it’s use they would just use aluminium.

          • A 100 nanometer layer of aluminium can decay significantly in days in a hot and humid environment. And silver will reflect about 95% of the light while aluminium will only manage around 90%.

          • When sunlight hits a silicon cell, it generates electrons. Ever since practical solar cells have been made – about 60 years ago – silver has been used as a conductor to collect these electrons in order to form a useful electric current. Silver was originally chosen for this role because it is a high-conductivity metal. The average solar panel uses about one-half of an ounce of silver.

          • Juxx0r, maybe you should read back through what I have written and see if there is anything you disagree with.

          • I disagree with the premise that silver is used to reflect light back through the cells. Silver is used as a current collector. The reason why it is silver is because of it’s high conductivity. The real reason why it is silver is because it’s corrosion products also remain conductive to give plus 25 year lifespans. Its reflectivity is unrelated to it’s use in solar cells. I also disagree with this “If reflection wasn’t important I think they’d skip applying silver and just increase the aluminium paste wiring they print on the back” because the conductivity is the reason why it’s silver not the reflectance.

  • I’m confused by all the concern about lead in these solar cells. We currently have lead acid batteries in just about everything that moves and don’t seem to care a whit about adverse environmental impacts from the product. The chance of dispersing lead from perovskite solar cells has got to considerably less than what we already have with lead acid batteries.

    • Not to saying your point is invalid, but the lead in lead acid batteries is fairly easily recycled into new batteries and the public is encouraged to turn the old ones in for recycling with a cash incentive. I’m not sure if the lead in batteries is a real concern. I’d wager that lead from other, more insidious sources are a greater environmental concern if only because it can be so easily inserted into the waste stream or worse.

    • I agree with your point. The major problem with perovskite is moisture degradation so the cell will have to seal in any lead very carefully just to remain functional. A requirement that the cells be recycled at the end of life is trivial compared with what must be done for a nuke plant, for example. The lead concern is way overblown.

  • Hi Tina, As a person “on the go,” I loved your article. Thanks.

  • Solar PV already killed coal in the free market.

    Solar PV is coming for gas and nukes now.

    Watch out.

  • Die, coal, die!!

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