Solar PV with more than 40% efficiency is now achievable.

Remember back in February we had a look at progress in the brave new world of perovskite solar photovoltaic technology? You don't? Yeah you do. We looked at the UK firm Oxford PV and we discovered they were well on the way to full production of real commercial scale solar panels with an industry leading efficiency of 28.6% all as a result of their pioneering work on optimizing perovskite's potential. Anyway in the vanishingly unlikely event that you did miss that episode you can click up there somewhere to jump back and have a look. The reason I mention it now is because in early September 2024 Oxford PV began shipping its first consignment of perovskite PV modules to customers in the United States. That's very encouraging news in itself of course but Oxford PV are not the only organization developing this apparently miraculous material. Anyone who gets it right is probably looking at a bit of a goldmine quite frankly. So laboratories all over the world are working flat out to come up with the next breakthrough iteration and now a team over in China reckons they've perfected a process that produces verifiable perovskite solar PV cells that have a conversion efficiency that's higher than the so-called Shockley-Kweiser limit. What's the Shockley-Kweiser limit? Why are solar photovoltaics constrained by it? Can the Chinese team really be telling the truth? Why does it matter? What was that material called again? Yeah I know. Let's take a look. Hello and welcome to Just Have a Think. Before we get stuck in I must just let you know about the upcoming Everything Electric live show in Farnborough in the south of England this October. The Farnborough International Exhibition and Conference Centre is a massive venue with tons of outdoor space not just to display all the new private and commercial electric vehicles that are flooding onto the market but also to house some great attractions and safe areas for the kids to run around and have some fun. Inside the conference centre you'll find all the major suppliers of things like wall chargers, heat pumps, solar panels and battery energy storage solutions with experts on hand to guide you through the process of choosing the best system for your home. I'll be hosting several live discussion panels there across all three days so I'll be around to say hello if you do decide to come along. The whole thing kicks off on Friday the 11th of October and runs through to Sunday the 13th. Tickets are available now at the link on screen and in the description section below this video and if you use the exclusive Just Have a Think discount code shown at the bottom of the screen now then you'll get 20% off all tickets purchased. This one is the biggest event in the Everything Electric UK calendar folks so I'm really looking forward to it and I hope to see you there. Right back to today's topic and that encouraging news from Oxford PV. They've announced that their 72 cell solar PV modules are now being shipped from their new facility in Brandenburg an der Havel in Germany to commercial customers over in the States but I noticed they're now claiming a conversion efficiency of 24.5% for the final production version. That's significantly lower than the 28.6% that I mentioned earlier and that Oxford PV themselves still quote on their website. So why is that then? Well it's because the website is quoting cell efficiency while the shipped product is of course the fully assembled panel and that makes a difference. Individual cells have a higher efficiency than full panels simply because lining them up framing them up and covering them with protective material very slightly reduces the cell efficiency. I'm certainly not suggesting any skullduggery here either by the way. 24.5% is still roughly 20% better than any existing commercially available solar PV technology so it's not to be sniffed at. In a recent interview with the folks at PV magazine Oxford PV's chief exec David Ward said it is a major breakthrough for the energy industry that perovskite modules are now economically viable. Highly efficient technologies will dominate the future of the solar industry and that future has begun. The company suggested that technology like theirs which combines perovskite material with traditional silicon in a so-called tandem cell has the potential to reach an efficiency of 43%. I'll come back to that claim a bit later in the video but first let's just have a look at what this latest research paper from the Chinese research team says. The team itself includes material scientists from the Institute of Photovoltaics at Nancheng University, the Department of Applied Physics at Hong Kong University, the Wuhan University of Technology and the Institute of Optoelectronics at Fudan University. So you know, quite specialized. They reckon they've come up with a new organic coating that can increase the efficiency of what are known as monolithic tandem cells made of silicon and perovskite. And here's where we should probably pause for a moment and talk about that whole Shockley-Kweiser thing that I mentioned at the start of the video and how tandem cells can theoretically overcome the limitations set out by that law of physics. If you did watch my previous perovskite video earlier in the year then you'll already know all this stuff but it never hurts to have a little reminder does it? It's all to do with the way sunlight interacts with the materials in the solar cell or more specifically which wavelengths of light interact with those materials. Some atomic semiconductor structures can absorb a very wide range of wavelengths which is great because that means you're using a large amount of all the available sunlight. Trouble is those semiconductors typically only deliver a very small electrical voltage which is no good in a solar panel. Other atomic structures can provide a much higher voltage but you guessed it they typically only capture a very small range of wavelengths which means most of the energy in the sunlight is wasted. The optimal trade-off was established in 1961 by physicists William Shockley and Hans-Joachim Kweiser. They found that silicon was the optimum available material and that the maximum theoretical efficiency of a single layer photovoltaic cell was around 30 percent. So how does perovskite fit into the mix then? Well the science bods tell us it's an inorganic compound that can be produced very precisely and inexpensively at low temperatures in laboratories. It can be chemically manipulated or tuned to capture different wavelengths of light to silicon. Over a decade ago researchers started applying thin layers of perovskite film on top of silicon wafers and they found that by doing that they could absorb a far wider spectrum of light, maintain a good working voltage and in theory overcome that Shockley-Kweiser limit of 30 percent. And that started a whole field of tandem cell research that's still going on today. One of perovskite's major challenges is that it tends to degrade very quickly in sunlight so quite a lot of that last 10 years has been all about finding ways to make silicon perovskite cells reliable and stable enough to have a decent working lifetime in the real world and that has certainly been easier said than done. Oxford PV is leading the way and the company's working hard to produce production volume panels that can genuinely convert more than 30 percent of the sunlight received into useful electrical energy. They're also convinced that it won't be too many years before the technology reaches the 43 percent efficiency that I mentioned earlier, roughly double the output of any solar panels you might have on your roof right now. So this latest research over in China might just turn out to be a useful addition to that work. So-called monolithic tandem cells are made using a substrate of silicon wafers that are produced by something called a zone melting process and those wafers have a highly polished or nanostructured surface. There's also a cheaper alternative industrial system called the Czochralski process which produces silicon wafers with a tiny micrometer scale pyramid-like structure and which actually captures more light as a result. The slight wrinkle is that as soon as a second layer of perovskite is applied to the sandwich it introduces a whole bunch of defects into the lattice which messes up the ability of the structure to convert light into free electrons. The researchers on this paper have developed a novel strategy for something called surface passivation which is a process that smooths out those defects and makes the perovskite layer much more effective at capturing the relevant wavelengths of sunlight. The Chinese team have come up with an alternative that they describe as a dynamic spray coating process using a typically unpronounceable chemical combination called fluorinated thiophenethylene ammonium with a trifluoromethyl group which I finally got right after only 13 attempts. Apparently that combination has high polarity and binding energy which to you and me means it squishes nicely into all the tiny micrometer scale gaps and defects to smooth out any lumps and bumps on the perovskite surface. When they applied the spray coated perovskite to a standard textured wafer made using the Czochralski method I mentioned earlier they achieved a conversion efficiency of 30.89% which they've apparently had certified by independent assessors and the good news is it looks as though unlike some other lab-based initiatives that we've featured on the channel over the years this one might just stand the chance of actually being useful in the real world. Tests showed that devices fitted with these passivated cells displayed excellent operational stability retaining over 97% of their initial performance after 600 hours of continuous illumination. The full science of how it all works at molecular level is set out in intricate detail in the paper and is frankly well over my head. The paper itself is I'm afraid only accessible through a paywall so I can't share the copy that I purchased but I have left a link in the description section below to the summary page in case you're keen to find out more. So one more incremental step towards ever improving solar pv efficiency or just more lab-based hopium? I'm optimistic this one might turn out to be the former and not the latter but I guess only time will tell won't it? Feel free to leave your thoughts on the subject in the comments section below but that's it for this week. Thanks as always to the amazing folks who support my work via Patreon and I must just give a quick shout out to some folks who joined recently with pledges of ten dollars or more a month. They are Niels Herkild, Steve Dernal, Jay McIntosh, Tim Skea, Chris Wood, Robert Beck, Bob Covey, Eric Biggers, Stefan Miller, Werner Teinert, Joe Masti, Shab Kumar, Stuart Gullvin, Richard Holden, Matt V and Mike Crompton. 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