This tiny solar cell might be about to revolutionize solar energy as we know it. It's way more efficient than a standard silicon solar cell... it can be easily synthesized — so it doesn't need to be mined like silicon. And it can work on thin film to power your smart home speaker, but it can also go on your roof. Say hi to this crystal structure called perovskite. It promises improvements to solar cells that are almost too good to be true. But WHY would we even need new solar cells? Well for starters... ...the regular solar cells you know are made with silicon. And they are actually quite inefficient at converting sunlight into energy. Only about 20 to 25% of sunlight can be captured on a commercial size. But that silicon needs to be mined. And purified in energy intensive processes that require more than 1,000 degrees Celsius of heat. If you want to know more on this, we have a full video on that here. But a new material called perovskite might actually be able to solve all of this. To understand why they are so superior to your standard silicon cell, I went here: the Helmholtz-Zentrum in Berlin. They've been researching perovskites as sun absorbing materials for about a decade. And this is the guy in charge of the research: Steve Albrecht. He's even set world records for the most efficient perovskite solar cells. "So on a very basic level: What does perovskite look like?" "The term perovskite is a very generic term for a specific crystal structure, right. You can see that over there. So the crystal structure has the ABX3 formula and like, each component is a certain either element or a molecule. One of the most common combinations in this structure is methylammonium as the A on the corners, the metal lead for B in the center and the chloride or iodide as the X which form around the metal. But there is quite a vast range of materials that can be used and combined. And it's quite wild how easily these can be put together. "Oh, this is a lab environment!" But before we do that: security first as we are going to work with toxic lead with one of Steve Albrecht's colleagues. "You look a bit like a veterinarian." "Yes, these are veterinary gloves" Ok, time to get in our base materials. Matthew mixes methylammonium chloride and lead iodide to later create our ABX3 crystal structure. By the way, everything happens in these boxes so that no water or oxygen comes in contact with our precious perovskite. "What is now the advantage of these materials compared to silicon?" "I believe that one of the main advantages of perovskite over silicon as a material is the ease of processing. So, silicon is something that is relatively energy intensive to fabricate, but this is something that can be done at close to room temperature. It doesn't require much energy, so it's easy to do. Everything is relatively abundant and so it shouldn't be a bottleneck for production." So, these base materials are more abundant than silicon and are easier to process. Now we have the base materials, but how do we make a sun absorbing perovskite out of it? "So, I deposit the solution of perovskite and then it spins up quite fast, so something like 4,000 revolutions per minute. And then I drop on this anti-solvent solution and that drives the crystallization of the perovskite film." The method that Matthew is using here is called spin coating. But perovskite solar cells can also be directly printed onto surfaces, using similar processes to those used for printing newspapers. Another method is evaporating perovskites onto surfaces. Spin coating usually takes place in a lab environment and it can be tedious. Matthew accidentally dropped the glass. Not a big problem in a lab environment, but for commercial production this is not viable. Matthew gives it a second try and this time everything works. After the spin coating it goes onto a heating plate and the darkening shows us that the crystals are being formed. It works the same way as when salt water evaporates and you start to see the salt. "There are cells like this one here which are only made out of perovskite, but in many cases there's a silicon layer beneath them. These cells are called tandem cells and look like this. Right now, they are the most promising candidates when it comes to increasing the efficiency of solar cells. But at some point, it might be possible to abandon silicon completely. To test their tandem cells efficiency, the researchers at the Helmholtz-Zentrum use a sun simulator. It determines exactly how much sunlight is converted into electricity. "What kind of efficiency did we just measure?" "Here we measured almost 30%. Quite a nice achievement." "Why does a tandem solar cell reach that much more efficiency than single junction solar cells?" "Tandem solar cells make much more use of the incoming light. So we have our solar spectrum and the solar cells, they share the spectrum. The perovskite solar cell in this case makes use of the visible wavelengths. So everything that we can see by eye is then converted into perovskite solar cell into electrical energy whereas the infrared light passes through the perovskite cell and is then converted into silicon solar cell which is quite efficient in converting infrared light. So, they share the spectrum and each cell is very efficient in their region." It doesn't sound like that much, but Eike tells me this way, roughly 50% more sunlight can be converted into electrical energy. So more overall sunlight can be absorbed. But you can't buy any of these tandem solar cells yet, because before they go into serial production there is a lot of stuff that needs to be fixed. A major issue is the stability of perovskite structures used in tandem solar cells. Perovskite structures are easily put together at low temperatures as we saw earlier, but they also come apart easily. Even the charges that travel through the perovskite in a solar cell can create defects and destroy the perovskite structures. Also, external factors like moisture, heat, oxygen and UV light can break it down further and quickly decrease its record-breaking efficiency. This whole process is called degradation which researchers and companies are trying to fight with different forms of encapsulation. It seals off the solar modules from external influences and is an essential step for commercialization. Qcells which is part of a European academia and industry partnership, plans to develop commercial-size modules with an efficiency of 26% over a lifetime of 30 years. Oxford PV, a company founded by Oxford University graduates, has reached an efficiency of 28.6% and supposedly solved the degradation issue already. But both companies haven't published verifiable data yet. There also isn't even a lot of research on real world outdoor tests. "These are a lot of solar cells that you test here. Wow!" This is Carolin Ulbrich. She oversees the degradation tests of tandem solar cells at the Helmholtz-Zentrum. "At what kind of stabilities are we currently looking at here?" "Sometimes they fail after a few days, but sometimes they last for years." Ulbrich's team measured a loss of 20% in efficiency in just half a year. Other researchers, in Saudi Arabia for example, came up with similar results. For comparison, it takes silicon solar cells roughly 20 years to reach that level of degradation — a number that tandem solar cells would need to match. "Some companies say they already fixed this issue and are ready to go to market next year. Do you believe that's possible?" "We do sometimes hear rumors also at conferences, but they normally don't show the data. It's all very secret. I assume that they will in the next years produce samples and that is very important to do because then you can test them on your own sites, in PV-fields, and before you commercialize them, before you sell them to customers, you can test inside whether it's really true because it's really hard to say about these samples that we have out here — after one year - that they're going to last for 25 years." And until now, we've only talked about the technical side of things. But tandem solars have another thing coming: "If perovskite is going to go anywhere, it will need to be cheaper than ordinary crystalized silicon on a per watt basis." This is Jenny Chase. She has analyzed the solar market for 18 years and founded the solar analysis team at Bloomberg NEF. "They've got to beat them on the cost per watt, which is currently 12.7 US cents per watt, and it'll be 12 by next year." According to the International Renewable Energy Agency, since 2010, costs for electricity from solar have declined by 89% globally. It's now more expensive to install silicon panels than it is to make them. Meaning the limiting factors for solar aren't the manufacturing costs, but grid connection, land permits or labor for installation. "It really comes down to the company that solves the cost and the stability factor and manages to get these into stable volume production will make a lot of money. If nobody does, then solar will still get built." One company, that claims it has solved the degradation issue, is Oxford PV. It says that, together with partners, it can ship out modules in the middle of 2024 and that we'll have utility scale solar parks with tandem cells in 2026 or 2027. Looking at today's efficiency numbers, solar parks like that would generate 25% more energy than comparable silicon solar parks. Solar tandem cells have a great potential, but there are still a lot of things that need to fall into place for them to work. And I'm really really curious if they are actually going to be on the market next year already. How did you like the video? Please let me know in the comments and subscribe to our channel. We post new videos on the environment every Friday.
