New Pathway Emerges To Improve Polycrystalline Thin-Film Solar Cell Performance
Puzzling out and testing new ways to improve the efficiency of cadmium telluride (CdTe) polycrystalline thin-film photovoltaic materials is a typical day in the life of National Renewable Energy Laboratory (NREL) research scientists Matthew Reese and Craig Perkins. Like any good puzzlers, they bring curiosity and keen observation to the task. These skills led them, over time, to make an intriguing observation. In fact, their discovery may prove to be a boon for the next generation of several different types of thin-film solar cells.
When fragments of solar cell material are crystallized together, or “grown” — think of a piece of rock candy growing in layers in a cup of sugar — they create a polycrystalline solar cell. With many layers come many surfaces, where one layer ends and another begins. These surfaces can cause defects that restrict the freedom of electrons to move, reducing the cell’s efficiency. As the cells are grown, researchers can introduce specific compounds that minimize the loss of electrons at these defects, in a process called “passivation.”
Reese, Perkins, and Colorado School of Mines doctoral student Deborah McGott noticed that the three-dimensional (3D) CdTe solar cells’ surfaces appeared to be covered in a very thin, two-dimensional (2D) layer that naturally eliminated surface defects. This 2D passivation layer forms in sheets on the 3D light-absorbing layer as the cell is growing, in a standard processing technique that is used around the globe. Despite the ubiquity of this 2D passivation layer, it had not been observed or reported in the research literature. Reese, Perkins, and McGott believed 2D passivation was also occurring naturally in other thin-film solar cells, like copper indium gallium selenide (CIGS) and perovskite solar cells (PSCs). They realized that this observation could lead to the development of new methods to improve the performance of many types of polycrystalline thin-film cells.
To confirm their hypothesis, they discussed it with NREL colleagues in the CdTe, CIGS, and PSC research groups. Through many informal discussions involving coffee, hallway chats, and impromptu meetings, Reese, Perkins, and McGott arrived at an “aha” moment. Their CdTe and CIGS colleagues confirmed that, while their research communities were not generally trying to perform 2D surface passivation in the 3D light-absorbing layer, it was, in fact, occurring. The PSC researchers said that they had noticed a 3D/2D passivation effect and were beginning to intentionally include compounds in device processing to improve performance. The “aha” moment took on even more significance.
“One of the unique things about NREL is that we have large groups of experts with different pools of knowledge working on CdTe, CIGS, and PSC technologies,” Reese said. “And we talk to each other! Confirming our hypothesis about naturally occurring 3D/2D passivation with our colleagues was easy because we share the successes and setbacks of our diverse research in an ongoing, informal, and collaborative way. We learn from each other. It is not something that typically happens in academic or for-profit-based polycrystalline thin-film solar cell research, where information is closely held, and researchers tend to remain siloed in their specific technology.”
The details of Reese, Perkins, and McGott’s discovery are presented in the article “3D/2D passivation as a secret to success for polycrystalline thin-film solar cells,” published in the journal Joule.
Supporting Evidence in the Literature
To confirm their findings, McGott conducted an extensive literature search and found considerable supporting evidence. The literature confirmed the presence of passivating 2D compounds in each of the CdTe, CIGS, and PSC technologies. No mention was made, however, of the 2D compounds’ ability to improve device performance in CdTe and CIGS technologies. While many articles on PSC technologies noted the naturally occurring 3D/2D passivation effect and discussed efforts to intentionally include specific compounds in device processing, none suggested that this effect might be active in other polycrystalline thin-film photovoltaic technologies.
Polycrystalline thin-film solar cells are made by depositing thin layers, or a thin film, of photovoltaic material on a backing of glass, plastic, or metal. Thin-film solar cells are inexpensive, and many people are familiar with their more unique applications. They can be mounted on curved surfaces — to power consumer goods, for example — or laminated on window glass to produce electricity while letting light through. The largest market for thin-film solar cell applications, however, is for CdTe thin film on rigid glass to make solar modules. CdTe modules are deployed at utility scale, where they compete directly with conventional silicon solar modules. Currently, commercial thin-film modules are generally less efficient than the best single crystal silicon solar modules, making performance improvements a high priority for polycrystalline thin-film researchers.
Key Properties of 2D Materials
Reese, Perkins, and McGott’s team used surface science techniques combined with crystal growth experiments to show that the 2D layers existed at and passivated 3D absorber surfaces in the three leading polycrystalline thin-film photovoltaic technologies. They then analyzed the key properties of successful 2D materials and developed a set of principles for selecting passivating compounds.
Finally, the team outlined key design strategies that will allow 3D/2D passivation to be employed in polycrystalline thin-film photovoltaic technologies more generally. This is particularly important because each 3D material requires a specific passivation approach.
The literature results, combined with lab-based observations, show that 3D/2D passivation may be the secret to success in enabling next-generation thin-film solar cells, particularly if researchers freely share the knowledge developed for each technology. The lack of 3D/2D passivation may even shed light on the stalled performance improvements of some polycrystalline technologies such gallium arsenide. By drawing parallels between the three technologies, Reese, Perkins, and McGott hope to demonstrate how the knowledge developed in each can — and should — be leveraged by other technologies, an approach that is seldom seen in polycrystalline thin-film solar cell research.
CdTe, CIGS, and PSC thin-film research at NREL is funded by the Department of Energy’s Solar Energy Technologies Office. Additional funding for Reese and McGott’s research is provided by the Department of Defense’s Office of Naval Research.
Learn more about photovoltaic research at NREL.
Article courtesy of the NREL, The U.S. Department of Energy.
On today’s exciting episode of Quick Charge, we don’t even mention “you know who,” focusing instead on EV news from Rivian, Lucid, Nissan, Ford, and what it takes to make a MAN in the heavy truck space. Check it out!
Sure, Nissan is pushing back production estimates on its yet-to-begin-production Nissan LEAF and Ford’s EV sales were down significantly in Q2, but there’s more to the story than the “Faux News” crowd would have you believe. Plus: some new electric success stories from Porsche and a disappointing (but still cool) dive into some new home backup battery tech.
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he 30% federal solar tax credit is ending this year. If you’ve ever considered going solar, now’s the time to act. To make sure you find a trusted, reliable solar installer near you that offers competitive pricing, check out EnergySage, a free service that makes it easy for you to go solar. It has hundreds of pre-vetted solar installers competing for your business, ensuring you get high-quality solutions and save 20-30% compared to going it alone. Plus, it’s free to use, and you won’t get sales calls until you select an installer and share your phone number with them.
Your personalized solar quotes are easy to compare online and you’ll get access to unbiased Energy Advisors to help you every step of the way. Get started here.
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Battery electric cars sold today in Europe produce 73% less life-cycle greenhouse gas emissions than gas cars, even when factoring in production, according to new research from the International Council on Clean Transportation (ICCT). That’s a big improvement from 2021, when the gap was 59%.
Meanwhile, hybrids and plug-in hybrids haven’t made much progress. The study confirms what clean transportation advocates have been saying for years: If Europe wants to seriously slash emissions from its dirtiest mode of transport – ICE passenger cars, which pump out nearly 75% of the sector’s pollution – it needs to go all-in on battery EVs.
“Battery electric cars in Europe are getting cleaner faster than we expected and outperform all other technologies, including hybrids and plug-in hybrids,” said ICCT researcher Dr. Marta Negri. Credit the continent’s rapid shift to renewables and the higher energy efficiency of EVs.
The makeup of the EU’s power grid is changing fast. By 2025, renewables are expected to generate 56% of Europe’s electricity, up from 38% in 2020. And that’s just the beginning: the share could hit 86% by 2045. Since cars bought today could still be on the road two decades from now, the growing use of clean electricity will only boost EVs’ climate benefits over time.
Gas-powered cars, on the other hand, will stay mostly tied to fossil fuels as the cost and availability of biofuels and e-fuels are still uncertain.
Hybrids and plug-in hybrids only cut lifetime emissions by 20% and 30%, respectively, compared to gas cars. That’s partly because plug-in hybrids tend to run on gas more than expected. So while hybrids aren’t useless, they’re just not good enough if we’re serious about climate goals.
Countering EV myths with hard data
There’s been a lot of noise lately about whether EVs are really that green. The ICCT study takes aim at the bad data and misleading claims floating around, like ignoring how the grid gets cleaner over time or using unrealistic gas mileage figures.
It’s true that manufacturing EVs creates more emissions upfront – about 40% more than making a gas car, mostly due to the battery. But EVs make up for it quickly: that extra emissions load is usually wiped out after about 17,000 km (10,563 miles) of driving, which most drivers hit in a year or two.
“We’ve recently seen auto industry leaders misrepresenting the emissions math on hybrids,” said Dr. Georg Bieker, senior researcher at the ICCT. “But life-cycle analysis is not a choose-your-own-adventure exercise.”
ICCT’s new analysis includes emissions from vehicle and battery production and recycling, fuel and electricity production, and fuel consumption and maintenance. It even adjusts for how the electricity mix will change in the coming years – a key detail when measuring plug-in hybrid performance.
Read more: Volkswagen’s 47% BEV sales jump includes a 24% boost in the US
The 30% federal solar tax credit is ending this year. If you’ve ever considered going solar, now’s the time to act. To make sure you find a trusted, reliable solar installer near you that offers competitive pricing, check out EnergySage, a free service that makes it easy for you to go solar. It has hundreds of pre-vetted solar installers competing for your business, ensuring you get high-quality solutions and save 20-30% compared to going it alone. Plus, it’s free to use, and you won’t get sales calls until you select an installer and share your phone number with them.
Your personalized solar quotes are easy to compare online and you’ll get access to unbiased Energy Advisors to help you every step of the way. Get started here.
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![Here's our closest look at the Kia EV2 caught testing in the Alps [Video]](https://i0.wp.com/electrek.co/wp-content/uploads/sites/3/2025/07/Kia-EV2-closest-look.jpeg?resize=1200,628&quality=82&strip=all&ssl=1)
The EV2 may be Kia’s smallest electric vehicle, but it has a big presence on the road. Kia promises it won’t feel so small when you’re inside, thanks to clever storage and flexible seating. After a prototype was spotted testing in the Alps, we are getting our closest look at the Kia EV2 so far.
Kia EV2 spotted in the Alps offers our closest look yet
Kia first unveiled the Concept EV2 during its 2025 EV Day event (see our recap of the event) in April, a preview of its upcoming entry-level electric SUV.
Despite its small size, Kia claims it will “redefine urban electric mobility” with new innovative features and more. Kia has yet to say exactly how big it will be, but given it will sit below the EV3, it’s expected to be around 4,000 mm (157″) in length. The EV3 is 4,300 mm (169.3″) in length.
Looking at it from the side, it sits much higher than you’d expect, similar to Kia’s larger EV9. During an exclusive event at Milan Design Week in April, Kia gave a sneak peek of the interior.
Kia said the interior is inspired by a “picnic in the city,” or in other words, a retreat from the busy city life. With a flat-floor design and flexible seating, you can quite literally have a picnic in the city.
Although we’ve seen the EV2 out in public testing a few times, a new video provides the closest look at Kia’s upcoming electric SUV.
The video, courtesy of CarSpyMedia, shows an EV2 prototype testing in the Alps with European license plates. There’s also a “Testfahrt” sticker on the back, which translates to “Test Car” in German.
As the prototype drives by, you can get a good look at it from all angles. Like in past sightings, the front features stacked vertical headlights with Kia’s signature Star Map lighting. Even the rear lights appear to be identical to those of the concept.
The interior will feature Kia’s next-gen ccNC (connected car Navigation Cockpit) infotainment system. The setup includes dual 12.3″ instrument clusters and infotainment screens in a curved panoramic display. Depending on the model, it could also include an added 5.3″ climate control screen.
Last month, a crossover coupe-like model was spotted on a car carrier in Korea, hinting at a new variant. The new model featured a design similar to that of the Genesis GV60.
Kia’s CEO, Ho Sung Song, also recently told Autocar that a smaller, more affordable EV was in the works to sit below the EV2. Song said the new EV, priced under €25,000 ($30,000), was “one area we are studying and developing.”
With the EV4 and EV5 launching this year, followed by the EV2 in 2026, it could be closer toward the end of the decade before we see it hit the market. Next-gen EV6 and EV9 models are also due out around then.
The Kia EV2 is set to launch in Europe and other global regions in 2026. Unfortunately, it’s not expected to make the trip to the US.
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