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.
Illinois is expanding its EV charging network with $18.4 million in federal grants that were restored after being unlawfully frozen by the Trump administration. The grants come from the second round of the National Electric Vehicle Infrastructure (NEVI) program, which supports Illinois’s goal of registering 1 million EVs by 2030.
Governor JB Pritzker, Attorney General Kwame Raoul, and the Illinois Department of Transportation (IDOT) announced Wednesday that the money will fund 25 new fast charging stations along interstate corridors.
Each new station will include at least four DC fast charging ports, which can top up an EV from empty in under 30 minutes. In total, the projects will add 167 new charging ports across the state.
Illinois is slated to receive $148 million in NEVI funds through the federal Infrastructure Investment and Jobs Act. Last year, the first round of awards sent $25.3 million to 37 charging station projects. With this new round, IDOT has awarded $43.8 million so far, covering 62 projects and 349 charging ports.
Pritzker said, “I’m thankful for the quick action of our attorney general in the fight to restore these funds that President Trump was unlawfully withholding. With these resources rightfully coming back to Illinois, I look forward to taking another step forward in our continued efforts to expand EV infrastructure and boost local economies across Illinois.”
In May, Illinois Attorney General Kwame Raoul joined 16 other attorneys general in suing the Federal Highway Administration for withholding the remainder of the appropriated funds. A judge in June ordered the administration to release funding appropriated to Illinois and 13 other states. Raoul said, “I am pleased that our coalition’s work has resulted in this money finally reaching Illinois, which ultimately boosts our state’s economy.”
Illinois EPA Director James Jennings noted that these NEVI-funded stations will complement the more than 450 charging stations already supported by the state. “Together, state agencies are working to offer EV drivers multiple charging options at numerous locations, ensuring accessible and convenient travel throughout Illinois.”
The 25 projects selected were chosen through a competitive process last fall. IDOT says the next round of NEVI funding applications will open in late 2025.
Read more: The biggest solar farm east of the Mississippi is now powering Chicago
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A Rivian owner and EV enthusiast recently shared images of a purple R1S Quad out in public with manufacturer plates. Could it be a new exterior color Rivian will offer customers, or is this just a rare shade applied to a one-off test vehicle? Regardless of its future, a purple Rivian is already garnering plenty of comments from the online community.
Rivian owner shares images of a purple R1S Quad
Hilbert (@Hilbe) shared the three images above on X, with the caption, “What do you think Rivian will name this color? Wrong answers only.” The answers are funny, and many are precisely what you probably imagined.
If you immediately thought Grimace from McDonald’s lore, so did I and several commenters to Hilbert’s post. Upon doing some digging, I found that images of this exact purple Rivian were actually leaked eight months ago, making their way through the Rivian community on Reddit. See below:
As you can see from the second image above, this Quad Motor R1S is donning manufacturer plates, meaning this isn’t a custom paint job from a personal owner, but a bona fide model still owned and operated by Rivian.
Furthermore, those plates are the same in multiple sightings, hinting that there is currently only one purple Rivian R1S Quad out in the world (at least on public roads).
Whether this is just a unique color the paint shop experimented with on a one-of-a-kind test vehicle or could become an actual option in the Gear Shop remains unclear at this time, although we did reach out to a representative for Rivian for more details and received an expected response:
We have nothing to add. As you know, we don’t comment on any speculation.
They didn’t say that purple was off the table (or the configurator!)
Rivian’s R1S and R1T configurator could use purple or any other unique exterior color options, as its boldest currently available option is “Rivian Blue.” Be sure to let us know what you think about a purple Rivian in the comments, much like X users did for Chris Hilbert, of which I read through all 130+ and have a few to highlight below.
I will stick to the PG responses and leave out anything related to an eggplant emoji and how that may have anything to do with any fictional purple characters (you sick puppies). Here we go:
- “Gross Purple”
- “Barney”
- “Purple Rain”
- “Plum Crazy”
- “Thanos Purple”
- “Violet Beauregarde”
- “Purivian”
- “Electric Eggplant”
- “Grape Ape”
- “Amethyst Twilight”
- “Afternoon Purple IV”
- “Grape Escape”
- and last but not least… “Poiple.”
What would you call this shade? Should Rivian bring purple to the Gear Shop configurator? Let us know in the comments below. As a Rivian owner, I highly recommend doing a test drive to see what this brand is about. Afterward, email me and let me know what you thought of your ride. I’m interested to hear about it!
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The US virtual power plant (VPP) market is growing fast, with 37.5 gigawatts of behind-the-meter flexible capacity now online, according to a new Wood Mackenzie report. VPPs connect small energy systems and smart devices into a single network managed by an energy company or utility. That can include residential solar panels, battery storage, EVs, and smart thermostats. When the grid needs help during peak demand or emergencies, they can be tapped – and you get paid for participating.
Wood Mackenzie’s “2025 North America Virtual Power Plant Market” report shows that the market is expanding more broadly than deeply. The number of company deployments, unique buyers (offtakers), and market and utility programs each grew by more than 33% in the past year. But total capacity grew at a slower pace – just under 14%. “Utility program caps, capacity accreditation reforms, and market barriers have prevented capacity from growing as fast as market activity,” said Ben Hertz-Shargel, global head of grid edge at Wood Mackenzie.
Residential VPP customers are gaining ground
Residential customers are making a bigger dent in wholesale market capacity, increasing their share to 10.2% from 8.8% in 2024. But small customers still face roadblocks, mainly due to limits on data access for enrollment and market settlement.
Battery storage and EVs are also playing a bigger role. Deployments that include batteries or EVs now account for 61% as many as those that include smart thermostats, which have long dominated VPP programs.
Leading states and markets
California, Texas, New York, and Massachusetts are leading the pack, making up 37% of all VPP deployments. In wholesale markets, PJM (which manages the electric grid for 13 states and DC) and ERCOT (the Texas grid), both home to massive data center commitments, also have the highest disclosed VPP offtake capacity. “While data centers are the source of new load, there’s an enormous opportunity to tap VPPs as the new source of grid flexibility,” Hertz-Shargel said.
Offtake growth and new business models
The top 25 VPP offtakers each procured more than 100 megawatts this year. Over half of all offtakers expanded their deployments by at least 30% compared to last year. That’s fueling the rise of a new “independent distributed power producer” model, where companies aim to use grid service revenue and energy arbitrage to finance third-party-owned storage for electricity retailers.
Policy pushback
Not everyone is on board with how utilities are approaching distributed energy resources (DERs). Many VPP aggregators and software providers oppose utilities putting DERs into their rate base under the Distributed Capacity Procurement model.* “This model is seen as limiting access of private capital and aggregators from the DER market, rather than leveraging customer and third-party-owned resources,” Hertz-Shargel explained. He added that most wholesale market experts believe FERC Order 2222 was a missed opportunity and won’t significantly improve market access.
*I really like this model, personally. I leased two Tesla Powerwalls under Green Mountain Power’s Lease Energy Storage program in Vermont for $55 a month, and it’s an excellent VPP program that’s grown much more rapidly than other models, such as bring-your-own batteries.
Read more: California’s grid gets a record power assist from a 100k home battery fleet
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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