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.
California’s ambitious statewide electric bicycle incentive program is officially dead – and it didn’t even get a funeral. After years of buildup, delays, and surging public interest, the California Air Resources Board (CARB) has quietly ended the program, rolling the remaining $17 million of the original $30 million budget into its “Clean Cars 4 All” initiative without even making an official announcement.
The California E-Bike Incentive Project was originally hailed as a groundbreaking effort to make electric bikes affordable for low-income residents. Vouchers – not rebates – were designed to let buyers walk into a participating shop and ride out without covering the full price upfront. Base vouchers were worth $1,000, with up to $2,500 available for those purchasing cargo or adaptive e-bikes in priority communities. It was a model that other states were watching closely.
But from the outset, the program was plagued by setbacks. Years of delays meant the first vouchers weren’t distributed until late 2024, and even then, only after a chaotic launch that saw the website crash under the weight of tens of thousands of applicants vying for just 1,500 vouchers. A second launch attempt in April 2025 failed completely, locking out eligible users. While a final distribution round in May went more smoothly, an estimated 90% of eligible applicants were turned away due to limited supply.
To make matters worse, the program’s administrator, Pedal Ahead, came under fire for questionable practices in San Diego, further undermining confidence.
Now, with no formal announcement or update on the program’s official website, CARB has quietly absorbed the funds into its Clean Cars 4 All program.
Electrek’s Take
This is an enormous letdown.
The California E-Bike Incentive Project had the potential to reshape car-heavy communities by giving low-income Californians access to clean, affordable micromobility. Instead, it was starved by mismanagement and then cannibalized to prop up car-centric policy.
It’s not that electric cars don’t deserve support, but this move reflects a broader failure of imagination. If we want a future with fewer cars, not just cleaner ones, then we need to start funding real alternatives. This was a huge missed opportunity to invest in a more livable California.
via: Streetsblog
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The Kia EV4 will be “delayed until further notice” in the US, according to a Kia rep and reported by InsideEVs. Kia said the change is because “market conditions for EVs have changed.”
The EV4 was expected to be released in 2026 at a price in the ~$30k range, entering Kia’s model like alongside the existing EV3 as the smaller, more affordable electric models below the EV6 and EV9. The EV4 will have the style of a boxy sedan, while the EV3 is a small SUV.
The EV3 is already available in Korea, Europe and other territories, but has not made it to the US (and may not ever).
The EV4 is not on the roads yet, but its release is imminent. And it seemed likely to make its way to the US. We saw the concept EV4 at the LA Auto Show in 2023, and the model was officially unveiled in the US at the New York Auto Show this April.
Bringing that car to a US auto show with an official reveal suggested that the US would get access to this smart, more affordable Kia. And Kia said that the car would hit US roads in early 2026, which would have been just a few months from now.
Kia abruptly “delays” EV4’s introduction to the US
But now, a Kia rep has confirmed that the car won’t come to America after all, at least until further notice. Kia gave a statement to InsideEVs, saying:
“Kia’s full range of vehicles offers meaningful value and inspiring performance to customers. However, as market conditions for EVs have changed, the release of the upcoming EV4 electric sedan will be delayed until further notice.”
We reached out to Kia to confirm, and received the same statement back.
The reversal is a bit of a surprise, and we’re not sure why we’re hearing this today in particular. Heck, we wrote a story about the EV4 GT’s interior just a couple hours ago.
So, unfortunately it looks like Americans will have one less potential choice to get away from the land-yacht disease currently infecting our populace. For what it’s worth, the EV4 is still listed as “coming 2026” on Kia Canada’s website.
We’ve seen models get delayed suddenly before, and while Kia did not directly say that the model will never come to the US, the fate of other “delayed” EV models in the past does not give us significant hope. Usually, a “delay” like this ends up meaning that the car just won’t ever make it to US roads (see: VW ID.7, Gen 2 Kia Soul EV, Ram 1500 EV, and others).
While Kia did not state a specific reason for the reversal, it’s not hard to guess what some of the influences are.
Electrek’s Take – EV4 likely delayed due to US policy changes favoring higher costs, dirty air
Since the EV4’s April reveal, republicans have continued their all-out assault on clean air, as in July a republican Congress passed a $4 trillion giveaway to wealthy US elites which also inflated the price of EVs by $7,500. Regulatory changes focusing on raising your costs and making your air dirtier are in progress, trying to force more gasoline and pollution on Americans and restricting access to cleaner, better EVs.
In addition to these actions opposing clean air, republicans are raising your costs in other ways as well. Unwise tariffs on basically every country in the world, which have been haphazardly implemented (due to the ignorance of the person unconstitutionally implementing them) and seem to change day-by-day, have increased prices for Americans and made business more difficult.
These tariffs would apply to the EV4. While Kia just started EV4 production in Europe, the US model would have come from Kia’s Korean factories. The ignoramus squatting in the US Oval Office did just ink a trade deal with Korea today, but given the lack of follow-through on previous trade deals, we wouldn’t be surprised if the terms of that change.
The difficulty of doing business in America has been in focus especially for South Korean firms, after a high-profile ICE raid at a Hyundai plant in construction in Georgia, which saw South Korean businessmen with visas detained and resulted in delayed construction on the plant and a swift popular pushback against US products in Korea. Kia and Hyundai are partner companies with a complex corporate relationship, so it stands to reason that Kia’s business decisions would be intertwined with Hyundai’s.
Many companies have recently cited a claimed but not substantiated lack of EV demand in the US as reasons for delaying their EV ambitions. To be clear, EVs have seen a long string of consistent sales growth in the US, stretching back more than a decade (with only a few interruptions to that growth, the largest being the start of COVID).
In the meantime, gas car sales peaked globally in 2017, and will never again reach that level of sales. This fact has been consistently underreported by media, alongside false headlines claiming EV sales are falling.
However, despite the record EV sales quarter the US just went through, it’s expected that the next year or so will see drops in EV demand. This is because of the pull-forward in sales experienced due to tax credit expiration, which caused a sales rush in Q3. Although, as has happened in other countries that suddenly ended purchase incentives, we’d expect perhaps a year of depressed sales before they begin to rise again.
But this likely drop in demand is hitting right around the same time the EV4 was supposed to launch in the US, so it’s not unreasonable for Kia to look at a market in a temporary downswing, especially when considering all the other factors laid out above (and the country’s current hostility to foreign investment, specifically investment from Kia’s partner company Hyundai), and wonder why they’ve gotten cold feet right now of all times.
While Kia didn’t lay out these reasons above in its statement, it sure seems likely that each of them could have had an effect on this decision.
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.
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New data from the Solar Energy Industries Association (SEIA) shows that the US solar supply chain has been fully reshored, with manufacturing capacity growing across every part of the solar and storage sector.
A US solar system from start to finish
With Hemlock’s new ingot and wafer facility coming online in Q3 2025, the US can now produce every major solar component domestically, from polysilicon to modules. According to SEIA, 65 new or expanded solar and storage factories have come online this year, bringing $4.5 billion in private investment to US communities.
However, SEIA warns that more than 100 factories and $31 billion in the pipeline could be at risk if the Trump administration continues its attacks on solar energy.
Solar manufacturing is booming – for now
The SEIA Solar & Storage Supply Chain Dashboard reports major capacity growth across every segment since late 2024. As of October 2025, US module production capacity has surpassed 60 gigawatts (GW), a 37% increase from December 2024. Solar cell production has more than tripled, jumping from 1 GW to 3.2 GW.
Battery cell manufacturing for stationary storage has climbed to over 21 gigawatt-hours (GWh), which SEIA says is enough to power the city of Houston from sunset to sunrise.
“This growth is a testament to the power of American innovation,” said Abigail Ross Hopper, SEIA’s president and CEO. “We’re building factories, hiring American workers, and showing that solar energy means made-in-America energy.”
Inverter manufacturing, which converts solar power into usable electricity, has jumped nearly 50% since the end of 2024, rising from 19 GW to 28 GW of capacity. Mounting system production is also up 14%, with 23 new factories added since 2024.
A pipeline under political threat
The US solar pipeline remains strong, with 23 GW of new module capacity, 34 GW of cell capacity, 25 GW of inverter capacity, and 95 GWh of battery cell capacity either under construction or announced. But SEIA says that Trump administration policies, regulations, and trade actions are creating uncertainty that could hurt progress.
“We’re seeing strong growth today, but that momentum isn’t guaranteed,” Hopper said. “If the administration continues down this path, they risk driving investment overseas, stifling job creation, raising costs on consumers, and handing America’s manufacturing advantage to our competitors.
“If the administration does not reverse its harmful actions that have undermined market certainty, energy costs will rise even further, and the next wave of factories and jobs could be at risk.”
Read more: The Trump administration just killed the US’s largest solar project
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.
FTC: We use income earning auto affiliate links. More.
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