Clean Power perovskite efficient solar cells

Published on July 3rd, 2015 | by Tina Casey


Perovskites Will Power New Low-Cost & Highly Efficient Solar Cells

July 3rd, 2015 by  

Since we’re celebrating Independence Day this weekend over here in the USA, we’re sharing this fireworksy image of perovskite crystals emailed to us by the folks at Los Alamos National Laboratory. Better known for its work on nukes, the lab has been hot on the trail of next-generation, super-efficient solar cells, and it looks like perovskite is the name of the game, partly because they are “more than a thousand times” less expensive than those fancy multi-junction solar cells.

perovskite efficient solar cells

First, The Bad News About Perovskite Solar Cells

For those of you new to the topic, perovskites refer to a class of earth-hued minerals first discovered in the 19th century in the Ural Mountains by Gustav Rose and named after the Russian mineralogist Lev Perovsky, which accounts for the Russian sounding name.

Perovskites are easily synthesized, and their distinctive crystalline structure makes them a perfect match for the development of efficient solar cells that can beat the current gold standard, which is silicon.

Perovskites may also play a role in next-generation electric vehicle batteries, according to some interesting maneuvers recently undertaken by Volkswagen.

Where were we, though? Oh, right, efficient solar cells. Perovskites look good as far as efficiency goes, but they tend to burn the candle at both ends. In other words, they are unstable. Like the rest of us, perovskites can take the heat but not the humidity, and they tend to fall apart in damp conditions.

In addition, until recently, perovskites were considered more expensive than other materials for commercial solar cells.

The Good News About Perovskite Solar Cells

Aside from being easily synthesized, perovskites are known to be easy to work with (that’s probably a dig at graphene, but whatever).

More to the point, despite the humidity thing, the research is rapidly advancing toward the design of a perovskite-based solar cell that provides stability with efficiency, as well as low cost.

One such advance consists of ditching lead, a toxic material used in conventional perovskite solar cells, and substituting low-cost, non-toxic materials. Alternatively, lead-based perovskite solar cells could provide a safe way to re-use lead from spent lead-acid batteries….

Coming up with a low-cost, low-energy manufacturing process is also critical for commercialization.

Combining perovskite technology with silicon is another path to next-generation efficient solar cells.


Even Better News

You can see elements of these approaches, and more, coming together in the perovskite research being conducted at Los Alamos National Laboratory (LANL), so if you’re in the mood for a long-form article, we do encourage you to check out the lab’s “Perovskite Power” article, published just last week.

The lab has come up with a reliable “recipe” for producing perovskite crystals that approach silicon in terms of solar conversion efficiency.

By reliable, the lab doesn’t mean defect-free, and that’s a critical point.

At first glance, perovskite crystals are inferior to silicon because of their relatively wide band gap (band gap is shorthand for how far electrons have to travel). However, LANL put that inferior characteristic to work, and developed a solar cell in which electrons bounce back and forth multiple times in a perfectly formed area, with only an extremely rare chance of venturing into an area of defect.

Here’s the happy recap from LANL:

As a result, the perovskite, while slightly worse than silicon in terms of its natural band gap, can be much more cheaply manufactured with excellent crystal purity.

The LANL secret sauce is a “hot casting” manufacturing process, in which a substrate is first heated, then coated with a solution containing perovskite crystals. While the process does require some energy input, it is a big improvement over conventional high-heat methods:

Unlike the complex crystal-growth methodologies used to make conventional, state-of-the-art semiconductor solar cells, solution processing is both fast and flexible. Fast means inexpensive, and the flexibility of liquid solution-based processing means the perovskite can be applied in convenient ways, such as spraying or painting the photoelectric layer directly onto a surface, opening the door to numerous new applications.

As for performance, in just six months, the lab has achieved an average of 15% conversion efficiency for its perovskite solar cells, topping out at 18%.

In contrast, LANL notes that after literally decades of research, conventional silicon solar cells in commercial use have reached about 20% conversion efficiency compared to the theoretical maximum of 33%. Multi-junction solar cells (multi-junction is fancyspeak for the use of multiple materials layered on top of each other) can reach 40%, but — here’s that money quote — perovskites are “more than a thousand times less expensive.”

Next steps for LANL include concentrating on beating silicon solar cell efficiency by subbing in a more tailored form of perovskite for the “generic” form used in the research, fine-tuning the manufacturing process, and developing more effective materials for the electrodes.

The big hitch is the aforementioned stability issue, and if LANL can’t quite crack that nut on its own, other up-and-coming perovskite research (here’s another example) indicates that solutions are close at hand.

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Image: High efficiency perovskite crystals courtesy of LANL.

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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+.

  • jnistler

    Another area that should not be ignored is the reduced energy related to fluidized pebble bed production of polysilicon (SunEdison) and the New Siemens process. In addition, new BOS approaches such as being done by PSIDA to reduce overall installation costs including full Solar Spectrum AC analysis of assembled systems is reducing prices per watt further. Large project funding is always concerned with the history of the company producing the product. Making it difficult for new technologies while monosilicon based technologies continue to improve in efficiency and price.

  • jnistler

    James, durability is the major issue with perovskite at this time. If stability can be obtained then the humidity issue is not a problem. I believe a majority of the issues on stability at this time is related to the lack of deposition studies using high vacuum equipment such as sputtering or CVD. A tandem junction would then make a lot of sense.

    Present solar cell production costs (best case) per watt is presently 30 cents. Epitaxial deposition of monosilicon has already been demonstrated reducing costs to ~ 15 cents per watt with stability over 30 years. Thus I believe that the idea of dual junction with monosilicon substrate does make the most sense if it could be combined with the HIT cell which is already demonstrating commercial efficiency > 25%. (Panasonic). We have also seen new improvements with Black Silicon. If this continues we will be looking at HIT structure in the >28% for commercially viable cells.

    So while perovskite structures are dealing with the stability issue (humidity related). Monsosilicon will drop in half on price and start to approach 28% in the next 2 to 4 years.

    • Bob_Wallace

      Interesting info…

      “Present solar cell production costs (best case) per watt is presently 30 cents.”

      That reminded me that I hadn’t check cell/module prices for a while. 30 (30.5) cents is now the average and low is 28 cents.

      “Monsosilicon will drop in half on price and start to approach 28% in the next 2 to 4 years.”

      About 80 cents for a 28% efficient cell? Any idea what the module cost might be at that point? Seems like that could really shake things up.

      • jnistler

        Understand these are projected costs. A ~ 497W module will cost ~ $238.54.

        • Bob_Wallace

          Well, if your projections are close then we’re looking at a lot cheaper solar coming soon. Moving to 28% efficient cells would cut a lot of racking and installation costs.

          Do you have any learned guesses at where the price of installed utility solar might be, say, five years from now? Continued price drops as we’ve seen or a steeper slope?

          • jnistler

            Bob, a good question. More than just technology goes into the LCOE which also includes ROI for the investors, financing and administration costs. Some of the present quotes are coming in at 5,5 cents per kWh. Combined wind and solar can bring this to the 4.8 to 5.2 cent today. I believe we will be at the < 4 cent per kWh range in the +/-15 degree latitudes by 5 year. Some sites with good level 2 wind and 15 to 30 degree from equator could reach <4 cents per kwh also. But many different factors come into play. Land cost, location, cost of capital, cost of labor, transmission lines and substation costs.

  • JamesWimberley

    For the record, the central application that the pioneers like Oxford Photovoltaics are aiming at is a tandem cell: a thin, transparent perovskite top layer picking up the shorter wavelengths, on top of a conventional silicon cell doing what it does best at the red end. Oh, you would also have a nanoengineered surface to improve the off-axis performance, but that technology is agnostic about the underlying cell type. This all only makes economic sense for a significant gain in overall efficiency, to something like 30%.

  • HollyJohnson

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  • PEB

    The benefits of perovskite are that: 1. It has a larger band gap than silicon so that it is sensitive to yellow light, which is where the Sun emits most of its energy. The Sun emits two to three times more energy in the yellow than the red, which is where silicon-base solar cells are most sensitive. So perovskite can capture twice as much solar energy as silicon. They have the potential to be 40% efficient compared to silicon’s 20%. 2. Defects in photo-sensitive materials such as silicon and perovskite destroys the band gap causing the material to be less efficient. With perovskites, the defects can be moved from the center of the band gap to the upper or lower edge, which helps keeps the efficiency of the material high. These are the two properties that make perovskite so attractive for photovoltaics.

    • Ronald Brakels

      Well, there’s not a huge difference between the amount of watts of red light and watts of yellow light hitting the earth’s surface from the sun. Of course, to compare them properly we’d need to define just what range or wavelengths count as red and which as yellow:

  • S Herb

    “band gap is shorthand for how far electrons have to travel”
    I’m afraid that this is quite wrong. The band gap determines the minimum photon energy required to create an electron-hole pair, and thus electric current. So a larger band-gap means that some of the low energy near-red photons will not contribute to the current from the perovskite cell.

    • Hans

      It also made my brain hurt. I think a basic physics class should be mandatory for CT writers.

  • rey

    Lev Perovski was Minister of Internal Affairs under Nicholas I of Russia. 19-century version of Lavrentiy Beria.

    Try to find story about Lev Perovski and “изумруд Коковина” (Kokovin’s emerald), for example.

    The mineral perovskite is named for him, as a “gift” to Perovski from Gustav Rose.

  • DecksUpMySleeve

    Really waiting on the first products efficiency, longevity, and price figures.

    If they can hit say, 13-14%, at 60 years(over 50% initial capacity), at half the price. I’d say we have a winner.

    • Will E

      current Solar Panels are Winners now.
      Prices of Solar Panels are low,
      politics and change of laws and regulations are the real problems for Solar and Solar pricing.
      not the price of silicon Solar Panels.

      • DecksUpMySleeve

        Yes, they are, though I think implementation is a bit off as well as political acceptance.
        Solar panels should be optimized for efficiency and longevity, with glass on both sides(double glassed), armored wires, aluminum dual axis tracking, built to run 100 years, and price calculated as such.

        Perovskite making a further cost leap could really boost adoption as well though, as will more advanced batteries of the near future.

        • Matt

          Dual tracking greatly raises cost/complexity or and failures. Much more so that single axis.

          • jeffhre

            Dual glass as well. And armored wires? Today’s panels may last 60 years as built.

          • DecksUpMySleeve

            I disagree. I think they can reach up to 300 years(ending up around 25% intial efficiency).
            The first crude panels we made still run well 40 years later and we make a far more standardized and for most companies a superior product.

          • Jacob

            We need the media to take photos of 40 year old solar PV installations.

            They have shown us a 40 year old wind turbine that is still producing electricity.

          • DecksUpMySleeve

            With a poor design yes.
            Got my own plan in mind.

        • Ross

          100 years is a needlessly long target. Solar panels will improve every decade and the investment terms are much shorter than 100 years. Who knows what the power source will be in 100 years. Fusion might be ramping up by then.

          • Jacob

            Fusion is useless for remote villages.

          • Ross

            Yes. In all probability. Even if there’s a breakthrough it is hard to imagine renewable energy being displaced completely. Fusion might come in handy for powering the synthesis of chemical fuel for all the re-useable rockets we’ll probably we using to move out into the solar system 100 years from now.

          • DecksUpMySleeve

            Aware, but if the calculate the pricing and return on investment as such it’s likely to spread like wildfire.
            Right now we can’t wait on the future, we’ve got a bucket with more holes than a bottom. We’re in 6X, we can’t keep mining coal, oil, spewing methane, mecury, sulfur, carbon. The balance of the planet requires out immediate shift unless we want food/water shortages, a large part of nature deleted, as well as Human populace, global strife and desperate wars by 2070.
            Our future won’t be there at present course. We can’t wait on the ultimate solution for a long time investment. Also, an abundant source like fusion will become a next wave weapon, a laser or something we can’t properly brandish as a species.
            There are solutions atm, advanced enough not to give a monkey a handgrenade, we should use them and safeguard our future.

    • Jouni Valkonen

      On the other hand, there is huge potential to improve the the price efficiency of conventional silicon and CIGS cells. Therefore I would say that perovskite cells are not long term winners.

      Energy consumption is a non-issue, because solar panel manufacturing plant can be self-loooped. I. E. Panel factory is renewable energy powered, similarly as Tesla Gigafactory will be.

      • DecksUpMySleeve

        Perovskite is about low material cost, with the right production they could win the cost/kWh battle. Yet to be seen.

  • JamesWimberley

    ” .. a substrate is first heated, then coated with a solution containing perovskite crystals.” In my uninformed way I thought that crystals were a feature of the solid state. Please explain. IIRC one of the advantages of the perovskite structure is that is a low-energy one, that will form naturally in a range of conditions. The alchemy is to tweak the conditions and materials to get the particular perovskite you want.

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