Superlattice Solar cells produce a thousand times more power

The photovoltaic effect of ferroelectric crystals can be increased by a factor of 1,000 if three different materials are arranged periodically in a lattice. This has been revealed in a study by researchers at Martin Luther University Halle-Wittenberg (MLU).

They achieved this by creating crystalline layers of barium titanate, strontium titanate and calcium titanate which they alternately placed on top of one another. Their findings, which could significantly increase the efficiency of solar cells, were published in the journal Science Advances.

Most solar cells are currently silicon based; however, their efficiency is limited. This has prompted researchers to examine new materials, such as ferroelectrics like barium titanate, a mixed oxide made of barium and titanium.

โ€œFerroelectric means that the material has spatially separated positive and negative charges,โ€ explains physicist Dr Akash Bhatnagar from MLUโ€™s Centre for Innovation Competence SiLi-nano. โ€œThe charge separation leads to an asymmetric structure that enables electricity to be generated from light.โ€

Unlike silicon, ferroelectric crystals do not require a so-called pn junction to create the photovoltaic effect, in other words, no positively and negatively doped layers. This makes it much easier to produce the solar panels.

However, pure barium titanate does not absorb much sunlight and consequently generates a comparatively low photocurrent. The latest research has shown that combining extremely thin layers of different materials significantly increases the solar energy yield. โ€œThe important thing here is that a ferroelectric material is alternated with a paraelectric material. Although the latter does not have separated charges, it can become ferroelectric under certain conditions, for example at low temperatures or when its chemical structure is slightly modified,โ€ explains Bhatnagar.

Bhatnagarโ€™s research group discovered that the photovoltaic effect is greatly enhanced if the ferroelectric layer alternates not only with one, but with two different paraelectric layers. Yeseul Yun, a Ph.D. student at MLU and first author of the study, explains: โ€œWe embedded the barium titanate between strontium titanate and calcium titanate. This was achieved by vaporizing the crystals with a high-power laser and redepositing them on carrier substrates. This produced a material made of 500 layers that is about 200 nanometres thick.โ€

When conducting the photoelectric measurements, the new material was irradiated with laser light. The result surprised even the research group: compared to pure barium titanate of a similar thickness, the current flow was up to 1,000 times strongerโ€”and this despite the fact that the proportion of barium titanate as the main photoelectric component was reduced by almost two thirds.

โ€œThe interaction between the lattice layers appears to lead to a much higher permittivityโ€”in other words, the electrons are able to flow much more easily due to the excitation by the light photons,โ€ explains Akash Bhatnagar. The measurements also showed that this effect is very robust: it remained nearly constant over a six-month period.

Further research must now be done to find out exactly what causes the outstanding photoelectric effect. Bhatnagar is confident that the potential demonstrated by the new concept can be used for practical applications in solar panels. โ€œThe layer structure shows a higher yield in all temperature ranges than pure ferroelectrics. The crystals are also significantly more durable and do not require special packaging.โ€

See more here: techxplore.com

Header image: Science Advances

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Comments (7)

  • Avatar

    Howdy

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    โ€œthe new material was irradiated with laser lightโ€ฆ. the current flow was up to 1,000 times strongerโ€
    So what, Itโ€™s output from the sun that matters. Whatโ€™s the output in that scenario?
    What sort of light?
    1000 times stronger than what?
    What are the costs, both environmental, and monetary, that includes creation of the device and dismantling afterwards? Or is it just more โ€œbury and no problemโ€, as at present.

    โ€œThe layer structure shows a higher yield in all temperature ranges than pure ferroelectrics. The crystals are also significantly more durable and do not require special packaging.โ€
    Yet the stated performance is only over 6 months so farโ€ฆ

    Yeah, not impressed.

    Reply

  • Avatar

    Charles Higley

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    The problem with solar power is two-fold. First, sunlight is only useful during part of the day and even less so with latitude and seasons. Second, excess energy has to be stored in batteries and this is an inefficient, environment-unfriendly, and expensive problem..

    Reply

    • Avatar

      sir_isO

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      I disagree about it being necessarily inefficient, environmentally damaging or expensive, relatively. Like, itโ€™s kinda pessimistic.

      Instead, optimistically, you can also say sunlight CAN be useful for electricity in the day and with batteries it can be stored for later use, too.

      Solar derived power is a massive thing, btw (since thatโ€™d include pretty much anything, unless you can find things on earth that didnโ€™t involve the sun, I guess).

      I mean, I understand youโ€™re mostly looking at it as โ€œThe solar panels and batteries being sold to usโ€. And in that sense, I agree mostly.

      So there are a LOT of ways to think about solar derived power. Directly, or indirectly. For instance, changing a process to use radiation to save on materials, energy inputs, etc. People looking for more generalized โ€œfuelsโ€ would probably look at hydrogen, methanol, formic acid, and similar shit.

      But for instance, in a desert area, you could probably use molten salt (solar) power plants with reflectors fairly justifiably.

      A serious problem is there is significant incentive to peddle artificial scarcity and legacy, stagnant shit for hegemony. Like say, homogenizing usage of lithium and rare earth metals. Thatโ€™s a problem with industry in general though. But, what ever happened to trying stuff with common, cheaper, safer elements? Iโ€™m pretty sure thereโ€™s an enormous amount of possibilities in like, sodium, calcium, potassium, magnesiumโ€ฆshit repurposing things like chlorine and fluoride and NOT toxifying their whatever with it.

      But yeah, efficiency might (or might not) be lower or whatever, sometimesโ€ฆbut often itโ€™s quite suitable, even if not for everything, and with significant other benefits. Sometimes shit is repressed simply because itโ€™s far more efficient.

      If thereโ€™s less of something, itโ€™s often easier to control. Kinda like CO2, I guess.

      Anyway, about the articleโ€ฆ
      Essentially they use interleaved crystalline metal layers, and the structure seems to make uh, resistance as well as โ€œeffectiveโ€ area more.

      They mention it was 1000x more efficient than barium titanate (which Iโ€™m assuming is low efficiency), so thatโ€™s your reference. What that translates to in terms of improvements over a typical consumer sort of panel, I dunno.

      Reply

      • Avatar

        sir_isO

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        err, resistance less

        Reply

  • Avatar

    Howdy

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    I know, Charles :). I guess my rant is because as we both know, Itโ€™s all wasted time and resources, plus damage caused, for not much back.

    Reply

  • Avatar

    JaKo

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    Photovoltaic solar energy at our latitude is a no-brainer. Anybody can calculate the costs and โ€œbenefits.โ€ About six years ago I calculated yearly loss of about $300 for installation of 2kW (~$5k) roof panels on our house; and thatโ€™s including all the gov. subsidiesโ€ฆ
    Cheers, JaKo

    Reply

  • Avatar

    JohnA

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    Anything to promote what is still a very expensive solution. It remains a problem that it useless when there is no sun.
    It is a highly polluting product during manufacture and disposal.
    It will still rely on hydrocarbons and coal for itโ€™s materials and manufacture.
    It is a niche market solution and one use where it is good is for powering space craft where there is plenty of financial resources available. Not so much for poorer communities.
    It still requires a back-up. Ask Germany -https://notrickszone.com/2021/05/02/europes-frosty-spring-germany-sees-coldest-april-in-40-years-frost-frequency-of-unusual-dimension/

    Reply

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