How the Next Big Solar Panel Tech is Already Here

Solar panels are typically made with silicon as their semiconducting material, but you know what they say ... the grass is always greener with cadmium telluride. Wait, what do you mean you've never heard of that? Well, I don't blame you. Cadmium telluride-based photovoltaics, or CDTE for short, are like that underrated indie band you've never heard of that's quietly building a cult following. Sure they're the second most common kind of panels after silicon PV, but when silicon still makes up the vast majority of the market by a long shot, that doesn't mean as much. So what on earth are cadmium telluride solar panels? And if they're already in use today, why are they the solar panel industry's best-kept secret? I'm Matt Ferrell ... welcome to Undecided. This video is brought to you by Lark ... but more on that later. For most people, CDTE probably sounds like something straight out of a high school chemistry quiz. But CDTE panels are far more common in the U.S. than anywhere else in the world. Before diving into why that is, let's take a moment to understand what CDTE even is. Cadmium telluride is a semiconductor material, just like silicon. As the name implies, it's made from cadmium and tellurium, both of which are toxic on their own, but safe when combined as CDTE. This isn't too unusual. Table salt, for instance, is made from two toxic substances, sodium and chlorine, that together form something essential to life. Cadmium is fairly easy to come by as a byproduct of zinc production. Tellurium on the other hand is rare, about as common as platinum, and is mostly found as a byproduct of copper mining. Since it doesn't have too many other uses, most of the tellurium mined goes straight into solar panels. So why use CDTE for solar? Like silicon, it has a band gap, which is basically an energy barrier that electrons need to cross to create electricity. Without going into too much jargon, CDTE has a band gap of 1.5 eV, which sits right in the sweet spot for solar cell efficiency. It's a bit higher than silicon's 1.1 eV, meaning it can absorb higher energy photons more efficiently without overheating. Even better, CDTE is a direct gap semiconductor, which makes it better at absorbing sunlight than silicon. And this is one reason why CDTE panels can be thinner and still generate decent amounts of power. Thinner panels are cheaper to produce and require less material, which is a big plus. Now, I know some of you are all about the numbers, so let's talk efficiency. CDTE panels typically hit around 18.6% efficiency, with lab versions reaching up to 22%. That's a little behind silicon's average efficiency of 20-24%, but we can push it above 22% with doping. That's the process of seeding material A with bits of material B, allowing us to port some of B's benefits to A's. In this case, we're seeding CDTE with conductive copper or arsenic. Which is super tasty. But CDTE has a secret weapon ... thinness. If you slim silicon panels down to the same thin-film size as CDTE, their efficiency drops to a measly 6%. So CDTE wins the thin-film competition hands down. But what about perovskites? They're like the solar industry's equivalent of a solid-state battery, always just a few years away from greatness. These materials can reach an impressive 26.7% efficiency. The catch? Perovskites are notoriously fragile and degrade quickly when exposed to heat, moisture, and even sunlight. Which is kind of ironic for a solar panel. Until we can toughen them up, CDTE's durability keeps it in the game. The U.S.-based company First Solar, more on them in a minute, is a major CDTE manufacturer and claims their panels maintain over 89% of their original performance after 30 years. That's a big deal for long-term solar installations. So while cadmium telluride isn't as efficient as perovskites, it's more reliable, easier to produce, and already widely available. That's right, CDTE isn't just mature, it isn't just commercially viable, it's kind of commonplace. Like I said, it's actually the second most common PV technology on the market right now. Second only to silicon. And that naturally raises the question, if it's already here, then where is it? Because we almost always hear about silicon, but not cadmium telluride. And speaking of something that's right under our noses, but goes unnoticed most of the time, it's plastics. It's in almost all of the products we buy, and unfortunately single-use plastics are a major issue. Well, today's sponsor Lark has a great way to challenge yourself to get as much one-time use plastic out of your life as you can. Their newest is the Lark Bottle Pure Viz 2, which purifies water, tracks your hydration habits, and gives you reminders to drink. It has some really cool tech inside to not only filter the water, but purify it. It uses UVC LED technology to automatically purify the water every two hours, and the filtration removes things like PFAS and chlorine, so you get safe, great tasting water. And if you're a tech geek like me, you'll love the new Lark mobile app that tracks how much water you're drinking, checks on your bottle filter life, and allows you to customize your hydration reminders. I know I definitely don't drink enough water myself, so this is a great way to reach your full hydration potential. If you'd like to cut out those one-time use plastics in your life and get fresh tasting pure water on the go, use the link in the description below to order yourself a Lark Bottle Pure Viz 2. I'm really loving mine. Thanks again to Lark and to all of you for supporting the channel. Now back to the question, if CDTE is here, then where is it? A number of companies began experimenting with them all the way back in the 1950s, with General Electric leading the charge. However, CDTE panels didn't really gain traction until the 1990s, when efficiency improvements made them more practical for solar power. Then came the market downturn in the early 2000s, which caused most companies to abandon cadmium telluride altogether. But not everyone gave up. One company stuck it out, and that's First Solar. First Solar's roots go back to Harold McMaster, a glass industry pioneer who initially found SolarCells, Inc., and had a vision for producing low-cost, thin-film solar panels on a large scale. Though he started with silicon, a friend convinced him to pivot to CDTE, which ultimately set First Solar on the path to success. The company launched its first commercial CDTE product in 2002, and since then they've been steadily increasing both the efficiency of their panels and their output. As of 2023, First Solar has an energy production rate of 16.6 GW and a commercial module efficiency of 19.3%. And that's just in the field. In the lab they've pushed cadmium telluride efficiency up to 23.1%, as confirmed by the U.S. National Renewable Energy Laboratory. First Solar claims they're on track to deliver a cell with 25% efficiency by 2025, and they're targeting 28% by 2030. While traditional single-junction silicon PVs are predicted to max out at 32.1% efficiency, cadmium telluride has a theoretical ceiling of 35.79%, so there's still a lot of potential left to unlock. What sets First Solar apart is their manufacturing speed. They can produce a fully functional CDTE panel in just 4.5 hours, thanks to a process called physical vapor deposition, or PVD. This process involves heating materials under a vacuum, causing them to vaporize and then condense onto a cooler surface, forming a thin, uniform film. It's a well-understood technique in the semiconductor world and is highly efficient for producing CDTE solar panels. On top of that, First Solar is dedicated to making their panels as environmentally friendly as possible. Compared to crystalline silicon, their cadmium telluride panels only require about 1-2% of the semiconductor material, resulting in a smaller carbon and water footprint. This helps cadmium telluride panels achieve some of the fastest energy payback times in the industry. In other words, CDTE panels pay for themselves in terms of energy savings faster than many other types of solar panels. And First Solar isn't stopping there. They're actively expanding their R&D capabilities and are currently building the largest solar thin film R&D center in the Western Hemisphere, located in Lake Township, Ohio. This new facility is expected to bring 300 new jobs by 2025 and help accelerate their advancements in CDTE technology. They're also integrating solar panel recycling. First Solar has developed a process to recover over 90% of the materials used in their panels, which is impressive considering the recovery rate for automotive materials is about 75% and general IT is just at 45%. Their process involves shredding and crushing the panels, separating the semiconductor material from the glass, and then refining the materials to be reused into new panels. This closed-loop system is a major step forward in reducing the environmental impact of solar panels. I actually have a video on a similar solar panel recycling technique and company that I'll link to in the description. And yes, solar panels can be recycled. If cadmium telluride is so popular, how come we really don't see it around us on a day-to-day basis like we do silicon? While I did say it's the second most common photovoltaic technology, I did bury the lead just a little bit. CDTE panels only make up about 21% of the photovoltaic market here in the United States as of 2022, where First Solar is based, but when you look globally, that number drops to just 4%. That's a huge gap. So why is cadmium telluride adoption lagging so far behind silicon? Well, cadmium telluride is not without its drawbacks. I already hit on the toxicity, which is going to make end-of-life recycling more critical. And I should note that even though tellurium isn't expensive, its rarity is still a limiting factor. Though ironically, one of cadmium telluride's biggest strengths might be a major weakness. You see, the copper doping methods that boost CDTE's efficiency to competitive levels also shorten its lifetime. Talk about a toxic relationship. According to the National Renewable Energy Laboratory, copper tends to move around within the cadmium telluride cells over time, eventually degrading the lattice structure of the material. NREL and First Solar are working to solve this problem with a process called copper reduction, nicknamed CURE, that optimizes the amount of copper used or even replaces it with arsenic. These efforts have already helped to reduce the degradation rate to just 0.2% per year. Another significant challenge with CDTE is its open circuit voltage, or VOC, which is essentially the maximum voltage that a cell can provide under no load. While CDTE should theoretically have a higher VOC due to its material properties, the copper doping introduces imperfections that lower this voltage. This creates a tough balancing act. Improve efficiency through doping, or focus on boosting the open circuit voltage. It's a classic tradeoff. And speak of the devil, efficiency in general is another issue. At the time of writing this script, cadmium telluride panels are simply less efficient than silicon on average, even with doping or other material tweaks. Efficiency is the name of the game when it comes to solar power, and while CDTE's other benefits like smaller carbon footprints and faster energy payback times are important, lower efficiency is still a major sticking point. This also has knock-on effects. CdTe solar farms generally need to be up to 31% larger to produce the same amount of power as a silicon-based farm, which makes CdTe less ideal for residential or space-constrained applications. For researchers at places like NREL, the next big hurdles to jump are boosting CdTe efficiency to 25% or more and getting that open circuit voltage above 1. This might sound like small improvements, but they're critical for keeping CdTe competitive in the long run. Hitting these targets will require optimizing several issues, from material composition to manufacturing processes, but let me quote from a paper published last year in the Journal of Solar Energy Materials and Solar Cells. Many of these goals have been realized separately, and the research and development community is working hard to integrate these innovations together to keep the rapid growth trajectory of CdTe technology moving in order to supply renewable electricity worldwide at terawatt scale. That said, the real final boss for CdTe doesn't lie with any of these issues. It's just that silicon is overwhelmingly popular. After all, it is very reliable, with very well-known strengths and weaknesses, and is widely available. Shifting a market without an overwhelming advantage is hard and takes time. People, power companies, and investors really do prefer the devil they know over the one they don't. So, is it CdTe's time to shine? It's getting there, but the future isn't set in stone. One major player in the future of cadmium telluride is China. As the world's largest producer of solar panels, it's no surprise that several Chinese companies are showing interest in CdTe. For example, Advanced Solar Power, based in Hangzhou, has been working on CdTe since at least 2011, with efficiency rates that are close to those of First Solar. Flat Glass Group, the world's second-largest PV glass manufacturer, recently invested 3 billion yuan into a 1GW CdTe solar cell facility. And China National Building Materials, or CNBM, is teaming up with the German company Singulus to ramp up CdTe production by using advanced vacuum coating machines. This partnership is expected to boost CNBM's CdTe production capacity to over 1GW annually. While cadmium telluride is stuck playing second fiddle to silicon for now, it might not be that way for too much longer. There's just so many possible paths forward that it's plausible that cadmium telluride will continue to rapidly improve and overtake silicon for solar farms and other large-scale projects. Then again, it's not like silicon isn't also advancing. Its popularity and market dominance are probably going to be hard to shake. Though I'm sure durable, green, thin-film tech like cadmium telluride will at least find a niche. In the end, it's hard to predict where this will go next. The space is advancing rapidly, and we hopefully won't have to wait too long to find out. But what do you think? Is cadmium telluride something you'd want on your house or project? Jump into the comments and let me know. And be sure to listen to my follow-up podcast, Still to be Determined. We'll keep this conversation going. Thanks as always to my patrons for your continued support. It really helps to keep the channel going. I'll see you in the next one.