{"id":9454,"date":"2024-06-18T08:17:58","date_gmt":"2024-06-18T12:17:58","guid":{"rendered":"https:\/\/undecidedmf.com\/?p=9454"},"modified":"2024-06-16T10:36:39","modified_gmt":"2024-06-16T14:36:39","slug":"how-quantum-dots-could-make-the-most-efficient-solar-panel","status":"publish","type":"post","link":"https:\/\/undecidedmf.com\/how-quantum-dots-could-make-the-most-efficient-solar-panel\/","title":{"rendered":"How Quantum Dots Could Make the Most Efficient Solar Panel"},"content":{"rendered":"

Ever heard of a quantum dot? What about an artificial atom? Though it might sound like technobabble from Star Trek (which of course I\u2019m a fan of), this is a real piece of nano-technology that has the potential to revolutionize fields like medicine, consumer electronics, and especially solar energy. Actually, quantum dot technology has been in TVs for years, so why isn\u2019t it already in my solar panels? Well, there are a few challenges\u2026 some which might sound familiar to you if you\u2019re in-the-know when it comes to cutting edge solar tech. If we can engineer around these challenges, then these little devices could have a BIG impact – breaking the limits of our current solar panels, and ushering in a new and radically more efficient age of solar energy.
\n<\/p>\n

What is a Quantum Dot?<\/h2>\n

What even is a \u201cquantum dot\u201d (QD)? While it sounds like a mcguffin that Stan Lee and Jack Kirby would\u2019ve thought up in the mid-sixties, it is in fact the real scientific term. But it’s also unhelpfully nondescript, so let me explain. Quantum dots are microscopic, crystalline semiconducting particles that could make our solar panels much more efficient. How much more? Well the theoretical maximum conversion efficiency for single-junction solar cells is around 30% efficient. We can add more junctions, like 6 of them, to bump up that theoretical max efficiency to 51.4%.1<\/a><\/sup> The National Renewable Energy Laboratory (NREL) calculated the theoretical max efficiency of quantum dot solarcells (QDSCs) at a staggering 66%!2<\/a><\/sup> And they\u2019re (theoretically) much easier to pull off than multijunction cells. If we can make them work, then quantum dots could change everything.<\/p>\n

That might make you wonder, like it did me, how do they do this? Quantum dots are so small that their electrons can only move in very specific ways. They\u2019re \u2018locked in\u2019 at very specific band gaps, which means they only produce very specific wavelengths of light (or in other words they emit very specific colors). We call this phenomenon \u2018quantum confinement.\u20192<\/a><\/sup> This is really strange when you think about it: these vials contain exactly the same material<\/a>,3<\/a><\/sup> down to an atomic level. Yet, they\u2019re glowing vibrantly in extremely different colors. The only thing differentiating them is their size.3<\/a><\/sup> The biggest and reddest ones tip the scale at 10 nanometers, while the smallest and bluest quantum dots are just 2 nanometers in diameter.2<\/a><\/sup><\/p>\n

For comparison a human hair is 80,000 to 100,000 nanometers thick. Your blood cells are 10,000 nanometers across. Even a single strand of DNA is about 2.5 nanometers wide.4<\/a><\/sup>5<\/a><\/sup> Quantum dots are so small that, for almost all intents and purposes, they\u2019re considered zero-dimensional. And at this size things start to get weird, and the laws of physics seem to start to break, like with the quantum confinement we mentioned a moment ago. To really understand how quantum dots are breaking these laws to make photovoltaic cells more efficient, we have to brush up on these laws of physics and how they work with solar cells.<\/p>\n

How Solar Works<\/h2>\n

At its core, a solar cell is a crystal with a positive (p) side and a negative (n) side, forming a p-n junction. The sun shoots out photons and eightish minutes later they hit our cell. If that photon has an energy level greater than or equal to the band gap energy of the cell, it\u2019ll transfer its energy to an electron, knocking the electron free from its home and creating an electron-hole pair. If not, then that energy is wasted. The \u2018free\u2019 electron and hole want to rejoin and\/or settle down, but if they remain free long enough they might pass through the electrode and bam! We got free energy from the sun.6<\/a><\/sup><\/p>\n

Even though we tried to simplify that, it\u2019s still a little complicated. You don\u2019t have to be an engineer to notice that there\u2019s some big \u201cifs\u201d and \u201cmights\u201d in that explanation. Solar panels actually aren\u2019t all that efficient. Most commercial panels can only convert 15-23% of the light that hits them into usable electricity.7<\/a><\/sup>8<\/a><\/sup> And solar panels won\u2019t get much more efficient, at least not the way we currently understand them. All the way back in 1961, scientists William Shockley and Hans-Joachim Queisser calculated that the maximum possible efficiency for single junction solar cells to be about 30%. Thankfully, with modern advances in materials and engineering, that max efficiency now stands at a mighty\u2026 33.7%. Aw, man.9<\/a><\/sup><\/p>\n

QDSC: The Shockley-Queisser Limit Breaker<\/h2>\n

Why is the Shockley-Queisser limit so low? In addition to all the hoops to jump through we mentioned earlier, there\u2019s a lot of factors that limit how much juice we can squeeze out of a photon. Luckily there might be a few loopholes. For instance, Shockley and Queisser assumed there\u2019s only one p-n junction. However, we could always add more semiconductors to create more band gaps. Remember that band gaps only generate energy from a photon if the photon has the same or greater energy level – they\u2019re picky eaters.10<\/a><\/sup>11<\/a><\/sup> So combining a bunch of them together to form what\u2019s called a multi-junction cell is a feasible way to break the Shockley-Queisser limit. It’s kind of like making a wider net to catch more energy levels of photons\u2026 or maybe it’s more like making a net with a bunch of back up nets behind it so less photons slip through? I\u2019m stretching that metaphor \u2026 anyway, this works great until you look at the price tag. Multi-junction PVs are expensive and hard to make (at least for now). For reference a typical solar panel costs well less than $1 per watt. For instance, an American made panel typically costs between $0.50 – $0.80 per watt.12<\/a><\/sup> However, even mere two-junction cells are estimated to cost around $4.85 – $7.17 per watt right now depending on the materials.13<\/a><\/sup> That cost will drop over time as manufacturing gets perfected, but it\u2019s why multi-junction cells aren\u2019t really commercially viable at the moment.14<\/a><\/sup><\/p>\n

And this is where quantum dots come back in. Since quantum dots are teeny-tiny semiconductors, we can use them to cheat something that works just like a multi-junction cell, potentially for less than a $1 per watt.16<\/a><\/sup>17<\/a><\/sup>18<\/a><\/sup> That\u2019s right, quantum dots are relatively cheap and easy to make, we can grow them by just mixing some high temperature solutions, and we can control how big they get with heat or time. Remember that the size of the dots changes how the electrons are confined, which changes their band gap and hue.1<\/a><\/sup> In a normal cell your absorption layer absorbs the same band gap of light. However, quantum confinement lets us cram a spectrum of different band gaps, even into the infrared spectrum, all precisely tuned to capture different wavelengths of light. At just a few nanometers in size, we can fit more quantum dots in a given space than semiconductors, which further helps to push their efficiency.15<\/a><\/sup>16<\/a><\/sup><\/p>\n

But wait, there\u2019s more! Multiple exciton generation (MEG) is another way quantum dot solar cells can get around the Shockley-Queisser limit. In a normal cell, we get one hole-pair (or exciton) per photon, if we\u2019re lucky. But quantum dots can create two or more excitons for each photon. Even though the mechanics of MEG are well understood, there\u2019s not yet a consensus on why it works. Anyway, you don’t\u2019 have to be a quantum physicist to understand that two excitons for the price of one is going to radically increase the efficiency of our solar cell.17<\/a><\/sup>18<\/a><\/sup> At the very least, it doubles the chance that something is going to make it to the electrode.<\/p>\n

Cutting Edge Quantum Dots<\/h2>\n

So with all the potential of quantum dots, you probably won\u2019t be surprised to hear that we\u2019re learning new things about them almost every day.<\/p>\n

<\/p>\n

A team of researchers from Korea University and the Ulsan National Institute of Science & Technology are trying to combine quantum dots with perovskites to get the best of both worlds. Perovskites are great, as we\u2019ve previously covered, but most of them are made primarily of lead and other toxic chemicals, which has raised concerns. That\u2019s why researchers have been leaning toward the less toxic tin\u2013lead halide perovskites (TLHP), but they\u2019re less powerful than their lead cousins and more prone to defects.19<\/a><\/sup><\/p>\n

To fix this the researchers added perovskite quantum dots (PQDs) to the cell, which both made the perovskites more stable and upped the maximum voltage of the cell. But now they had a new problem with ligands, which is the material the nano-crystals are suspended in. They were slowing down the charge transport. You can sort of think of it like having a very fast car, but hitting every red light on the way home. Doesn\u2019t matter what the speed limit is on the road if you have to stop at every block. The researchers treated their cells with a little isopropyl, which sort of loosened up the ligands and made everything gel together, creating better, smoother highways for the charge to \u2018drive\u2019 though. As a result their perovskite quantum dot cell was more efficient and faster, showcasing improved open-circuit voltage and a record-breaking conversion efficiency for tin\u2013lead halide perovskites.20<\/a><\/sup><\/p>\n

Meanwhile, a totally different team of scientists from several Korean universities and institutions just developed a flexible quantum dot solar cell based on all-inorganic cesium-lead iodide (CsPbI3) or \u2018black\u2019 perovskite. They can deposit a coat of these perovskite quantum dots quickly and at room temperature using a simple layer-by-layer process to create a flexible cell. The \u201croom temperature\u201d thing is particularly important, as you\u2019ll soon see, since quantum dots don\u2019t like too much heat. Ordinarily it takes some heat-treating to connect the perovskite quantum dots to the base layer of your cell, but this also increases the risk of defects. Being able to do this at room temperature should take a lot of the headache out of manufacturing them.21<\/a><\/sup><\/p>\n

And these cells weren\u2019t slouches either, the team reported power conversion efficiency of 12.70% under standard testing conditions.22<\/a><\/sup>23<\/a><\/sup> Commercial solar panels right now tend to hit around 20% so the technology has a ways to go, but 12.70% is still a new record for flexible quantum dots PVs.7<\/a><\/sup><\/p>\n

And this is all just from the last few months of 2024, but it’s not all sunshine and rainbows for quantum dots though. Despite the explosion of innovation, they are still a ways off. Despite their huge potential there\u2019s still some serious issues that need to be dealt with.<\/p>\n

The Challenges<\/h2>\n

I only briefly mentioned what quantum dots are made from, and that\u2019s because most formulations contain harmful metals like lead, cadmium, arsenic and mercury.24<\/a><\/sup>
\nThis has raised some concerns about toxicity, but the construction and recycling of quantum dots is comparable to standard solar. Where health and safety standards have been well established to deal with contaminants. Again, like standard solar, once in operation quantum dots don’t present issues because they\u2019re locked into the layers of that solar sandwich. What we don’t know is what the package of quantum dots and nanoparticles does to the human body.25<\/a><\/sup>26<\/a><\/sup><\/p>\n

Due to their small size, quantum dots could be inhaled or otherwise enter the body. An early study suggests that once inside, they can accumulate in organs with a lot of blood flow like the liver and kidneys, where they can cause inflammation and harm.27<\/a><\/sup> Though these questions are outstanding and more research is needed. For what it’s worth, a team from the Aligarh Muslim University in India has already begun work on making non-metallic, non-toxic quantum dots.28<\/a><\/sup><\/p>\n

Durability remains the biggest issue for quantum dot solar cells. Much like perovskites, quantum dots are sensitive and can degrade when exposed to air, moisture, and high temperatures (kind of like me). All things that a solar panel is expected to face for at least a decade or two.3<\/a><\/sup> They also don\u2019t like being illuminated too much or getting hit with a lot of ultraviolet light. Needless to say, a solar cell that can get a sunburn is not ideal. Again, I can relate. You also have to be careful about what material you pair with them. A solar panel is basically a sandwich filled with lots of different materials all aiding in the collection of sunlight or the protection of the sunlight-collectors. Quantum dots can react poorly with some materials and degrade even faster.29<\/a><\/sup><\/p>\n

One of the big advantages of current-gen solar tech, and the reason we see it (at least so far) still in use over less expensive or more efficient technologies, is their longevity. A solar panels\u2019 number one job is to change sunlight into electricity, but job number two is to do so reliably for years. While quantum dot solar cells might be radically more efficient, they are super-radically less durable, which means today\u2019s more basic solar tech has the edge (at least for now).3<\/a><\/sup> This isn\u2019t a problem when it comes to quantum dots other applications like medicine or high-def television screens. A bit ironic then that solar is the field where quantum dots have the most revolutionary potential, but also face the biggest hurdles.<\/p>\n

The potential for quantum dots to revolutionize the energy landscape makes them tantalizing. And the fact that they\u2019re already in QLED TVs make it feel like they\u2019re right around the corner for solar. And much like perovskites, if researchers can find an affordable way to make quantum dots more durable, then our solar panels are about to double in efficiency \u2026 but that\u2019s a pretty big \u2018if.\u2019 And if not? Well\u2026 quantum dots can still make our TVs, phones and especially medical devices better, and that\u2019s still pretty neat.30<\/a><\/sup><\/p>\n

<\/p>\n

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  1. Masafumi Yamaguchi, Frank Dimroth, John F. Geisz, Nicholas J. Ekins-Daukes; Multi-junction solar cells paving the way for super high-efficiency. J. Appl. Phys. 28 June 2021; 129 (24): 240901.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  2. Apoorva Panidapu, Why Size Matters: An Intro to Quantum Dots<\/a> \u21a9\ufe0e<\/a><\/li>\n
  3. PV Magazine, Quantum dot solar cells and the search for stability<\/a> \u21a9\ufe0e<\/a><\/li>\n
  4. National Nanotechnology Institute, Just How Small Is \u201cNano\u201d?<\/a> \u21a9\ufe0e<\/a><\/li>\n
  5. Nanosense, The Scale of Objects<\/a> \u21a9\ufe0e<\/a><\/li>\n
  6. Physics World, How can quantum techniques improve the efficiency of solar cells?<\/a> \u21a9\ufe0e<\/a><\/li>\n
  7. University of Michigan, Photovoltaic Fact Sheet<\/a> \u21a9\ufe0e<\/a><\/li>\n
  8. Market Watch, Solar Panel Efficiency Explained<\/a> \u21a9\ufe0e<\/a><\/li>\n
  9. Wikipedia, Shockley\u2013Queisser limit<\/a> \u21a9\ufe0e<\/a><\/li>\n
  10. American Chemical Society, How a Solar Cell Works<\/a> \u21a9\ufe0e<\/a><\/li>\n
  11. Kevin Zhang, Introduction to Quantum Dot Solar Cells<\/a> \u21a9\ufe0e<\/a><\/li>\n
  12. EnergySage – Where are solar panels made?<\/a> \u21a9\ufe0e<\/a><\/li>\n
  13. National Renewable Energy Laboratory, NREL, Swiss Scientists Power Past Solar Efficiency Records<\/a> \u21a9\ufe0e<\/a><\/li>\n
  14. Home Guide, How much do commercial solar panels cost?<\/a> \u21a9\ufe0e<\/a><\/li>\n
  15. Wikipedia, Quantum dot solar cell<\/a> \u21a9\ufe0e<\/a><\/li>\n
  16. Stem Bulletin, Solar Cells: Silicon Cells VS Quantum Dot Cells<\/a> \u21a9\ufe0e<\/a><\/li>\n
  17. Wikipedia, Multiple exciton generation<\/a> \u21a9\ufe0e<\/a><\/li>\n
  18. University of Queensland, Mysterious \u2018quantum dots\u2019 to revolutionize solar energy<\/a> \u21a9\ufe0e<\/a><\/li>\n
  19. M. A. Mubarok, Y. J. Kim, I. F. Imran, J.-H. Hwang, S.-H. Lee, H. J. Seog, S. K. Kwak, S.-Y. Jang, Regulating the Quantum Dots Integration to Improve the Performance of Tin\u2013Lead Perovskite Solar Cells. Adv. Energy Mater. 2024, 14, 2304276.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  20. TechXplore, Researchers report efficiency breakthrough for narrow-bandgap perovskite cells<\/a> \u21a9\ufe0e<\/a><\/li>\n
  21. Perovskite quantum dot solar cell achieves record-breaking efficiency of 12.70%<\/a> \u21a9\ufe0e<\/a><\/li>\n
  22. Kim, W., Kim, J., Kim, D. et al. Completely annealing-free flexible Perovskite quantum dot solar cells employing UV-sintered Ga-doped SnO2 electron transport layers. npj Flex Electron 8, 20 (2024)<\/a> \u21a9\ufe0e<\/a><\/li>\n
  23. Wikipedia, Energy conversion efficiency<\/a> \u21a9\ufe0e<\/a><\/li>\n
  24. National Renewable Energy Laboratory, Quantum Dots Promise to Significantly Boost Solar Cell Efficiencies<\/a> \u21a9\ufe0e<\/a><\/li>\n
  25. Ahmad, Farhan, et al. “Environmental applications and potential health implications of quantum dots.” Journal of Nanoparticle Research, vol. 14, no. 8, 1 Aug. 2012, pp. 1-24.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  26. Liu, Qing, et al. “New insights into the safety assessment of quantum dots: potential release pathways, environmental transformations, and health risks.” Environmental Science: Nano, vol. 9, no. 9, 2022, pp. 3277-3311.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  27. Liang, Y., Zhang, T., & Tang, M. (2022). Toxicity of quantum dots on target organs and immune system. Journal of Applied Toxicology, 42(1), 17\u201340.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  28. Phys Org, Cleaning up environmental contaminants with quantum dot technology<\/a> \u21a9\ufe0e<\/a><\/li>\n
  29. M. Albaladejo-Siguan, E. C. Baird, D. Becker-Koch, Y. Li, A. L. Rogach, Y. Vaynzof, Stability of Quantum Dot Solar Cells: A Matter of (Life)Time. Adv. Energy Mater. 2021, 11, 2003457.<\/a> \u21a9\ufe0e<\/a><\/li>\n
  30. M\u00f4nica A. Cotta, Quantum Dots and Their Applications: What Lies Ahead?ACS Applied Nano Materials 2020.<\/a> \u21a9\ufe0e<\/a><\/li>\n<\/ol>\n<\/div>","protected":false},"excerpt":{"rendered":"

    Ever heard of a quantum dot? What about an artificial atom? Though it might sound like technobabble from Star Trek (which of course I\u2019m a fan of), this is a real piece of nano-technology that has the potential to revolutionize fields like medicine, consumer electronics, and especially solar energy. Actually, quantum dot technology has been in TVs for years, so why isn\u2019t it already in my solar panels? Well, there are a few challenges\u2026 some which might sound familiar to you if you\u2019re in-the-know when it comes to cutting edge solar tech. If we can engineer around these challenges, then […]<\/p>\n","protected":false},"author":2,"featured_media":9482,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"video","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[249],"tags":[24,29],"ppma_author":[303],"aioseo_notices":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/undecidedmf.com\/wp-content\/uploads\/2024\/06\/Featured-1.jpg","authors":[{"term_id":303,"user_id":2,"is_guest":0,"slug":"matt","display_name":"Matt Ferrell","avatar_url":"https:\/\/undecidedmf.com\/wp-content\/uploads\/2021\/03\/portrait-small.png","user_url":"https:\/\/wordpressmu-787287-2686879.cloudwaysapps.com","last_name":"Ferrell","first_name":"Matt","job_title":"","description":"Matt Ferrell lives in the Boston area and is a UI\/UX designer by trade, but has always been obsessed by technology and how it works. In 2018 he started his YouTube channel, Undecided with Matt Ferrell, where he explores sustainable and smart technologies like EVs, solar panels, and smart homes."}],"_links":{"self":[{"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/posts\/9454"}],"collection":[{"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/comments?post=9454"}],"version-history":[{"count":7,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/posts\/9454\/revisions"}],"predecessor-version":[{"id":9486,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/posts\/9454\/revisions\/9486"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/media\/9482"}],"wp:attachment":[{"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/media?parent=9454"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/categories?post=9454"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/tags?post=9454"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/undecidedmf.com\/wp-json\/wp\/v2\/ppma_author?post=9454"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}