Perovskite is much more efficient than standard silicon solar cells. Its crystals are easy to synthesize and don't have to be mined like silicon. Perovskite could revolutionize solar technology.
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00:00This tiny solar cell might be about to revolutionize solar energy as we know it.
00:05It's way more efficient than your standard silicon solar cell.
00:08It can be easily synthesized and doesn't need to be mined like silicon.
00:12And it can work on thin film to power your smart home speaker, but it also can go on your roof.
00:18Say hi to this crystal structure called perovskite.
00:22It promises improvements to solar cells that are almost too good to be true.
00:28To understand why they are so superior to your standard silicon cell,
00:33I went here, the Helmholtz Institute in Berlin.
00:36They've been researching perovskites as a sun-absorbing material for more than a decade.
00:45And this is the guy in charge of the research,
00:47Steve Albrecht. He even set world records for the most efficient perovskite solar cells.
00:53So on a very basic level, what does perovskite look like?
00:58The term perovskite is a very generic term for a specific crystal structure, right?
01:04You can see that here, over there.
01:06So the crystal structure has the ABX3 formula,
01:10and like each component is a certain either element or molecule.
01:15One of the most common combinations in this structure is methyl ammonium as the A on the
01:20corners, the metal lead for B in the center, and chloride or iodide as the X,
01:27which form around the metal.
01:28But there is a vast range of materials that can be used and combined,
01:33and it's quite wild how easily these can be put together.
01:38Oh, this is a lab environment.
01:40But before we do that, security first,
01:42as we are going to work with toxic lead with one of Steve Albrecht's colleagues.
01:46Okay, looks good. I think you're good to go.
01:49You look a bit like a veterinary.
01:53Okay, time to get in our base materials.
01:56Matthew mixes methyl ammonium chloride and
01:59lead iodide to later create our ABX3 crystal structure.
02:05So what is now the advantage of these materials compared to silicon?
02:10So I believe that one of the main advantages of perovskite over silicon
02:15as a material is the ease of processing.
02:17So silicon is something that is relatively energy intensive to fabricate,
02:22but this is something that can be done at close to room temperature,
02:26so it doesn't require much energy, so it's easy to do.
02:29Everything is relatively abundant, and so it shouldn't be a bottleneck for production.
02:37Now that we have the base materials, we need to produce sun-absorbing perovskite out of it.
02:42Matthew does this by using a technique called spin coating.
02:46But perovskite solar cells can also be directly printed onto surfaces
02:51using similar processes to those needed for printing newspapers.
02:57Spin coating, however, can be tedious.
03:04Matthew accidentally dropped the glass.
03:06Not a big problem in a lab environment, but for commercial production, this is not viable.
03:11Matthew gives it a second try, and this time everything works.
03:15After the spin coating, it goes onto a heating plate,
03:18and the darkening shows us that the crystals are being formed.
03:22It works the same way as when salt water evaporates and you start to see the salt.
03:28There are cells like this one here which are only made out of perovskite,
03:32but in many cases there is a silicon layer beneath them.
03:36These cells are called tandem cells and look like this.
03:39Right now they are the most promising candidates
03:41when it comes to increasing the efficiency of solar cells.
03:45But at some point it might be also possible to abandon the silicon completely.
03:50To test their tandem cells efficiency,
03:52the researchers at Helmholtz Institute use a sun simulator.
03:55It determines exactly how much sunlight is converted into electricity.
04:00What kind of efficiency did we just measure?
04:03So here we measured almost 30 percent, a quite nice achievement.
04:07Why does a tandem solar cell reach that much more efficiency than single junction solar cells?
04:13So tandem solar cells make much more use of the incoming light.
04:18So we have our solar spectrum.
04:21The solar cells, they share the spectrum kind of.
04:24The perovskite solar cell in this case makes use of the visible wavelength.
04:30So everything which we can see by eye
04:32is then converted in the perovskite solar cell into electrical energy,
04:36whereas the infrared light passes through the perovskite cell
04:41and is then converted in the silicon solar cell,
04:43which is quite efficient in converting infrared light.
04:47So they share the spectrum and each cell is very efficient in their region.
04:52It doesn't sound like that much,
04:54but Eike tells me that this way roughly 50 percent more sunlight
04:57can be converted into electrical energy.
05:01So more overall sunlight can be absorbed,
05:03but you can't buy any of these tandem solar cells yet,
05:07because before they go into serial production,
05:09there's a lot of stuff that needs to be fixed.
05:12A major issue is the stability of the perovskite structures used in tandem solar cells.
05:17Perovskite structures are easily put together at low temperatures as we saw earlier,
05:21but they also come apart easily.
05:24Even the charges that travel through the perovskite in the solar cell
05:27can create defects and destroy the perovskite structures.
05:31Also, external factors like moisture, heat, oxygen and UV light
05:37can break it down further and quickly decrease its record-breaking efficiency.
05:42This whole process is called degradation,
05:44which researchers and companies are trying to fight with different forms of encapsulation.
05:49It seals off the solar modules from external influences
05:52and is an essential step for commercialization.
05:57Q-Cells, which is part of a European academia and industry partnership,
06:01plans to develop commercial-sized modules
06:04with an efficiency of 26% over a lifetime of 30 years.
06:10Oxford PV, a company founded by Oxford University graduates,
06:14has reached an efficiency of 28.6% and supposedly solved the degradation issue already.
06:21But neither company has published verifiable data yet.
06:25Nor is there a lot of published research on real-world outdoor tests.
06:31These are a lot of solar cells that you test here.
06:34Wow!
06:35This is Caroline Ulbricht.
06:37She oversees the degradation tests of tandem solar cells at the Helmholtz Institute.
06:42At what kind of stabilities are we currently looking at here?
06:46Sometimes they fail after a few days, but sometimes they last for years.
06:50Ulbricht's team measured a loss of 20% in efficiency in just half a year.
06:55It takes silicon solar cells roughly 20 years to reach that level of degradation.
07:00Some companies say they've already fixed this issue and are ready to go to market next year.
07:07Do you believe that's possible?
07:09We do sometimes hear rumors also at conferences,
07:12but they normally don't show the data.
07:14It's all very secret.
07:16Tandem solar cells would also need to price-match existing cells,
07:20a task that experts view as difficult to achieve,
07:23as costs for electricity from solar have declined by 89% since 2016.
07:30It's now more expensive to install silicon solar panels than to produce them.
07:36Solar tandem cells have a great potential,
07:38but there are still a lot of things that need to fall into place for them to work.
07:42And I'm really, really curious if they're actually going to be on the market next year already.