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.
Aptera’s clever new community funding program prioritizes your SEV delivery the more you invest
One week after sharing details of its Launch Edition Solar EV, Aptera Motors has announced a community funding program called Accelerate Aptera, hoping to raise between $20 and $50 million. By investing a predetermined minimum, reservation holders have a better chance at receiving delivery of one of the 2,000 Launch Edition Apteras planned. Better still, the person who invests the most on the leaderboard (yes there’s a leaderboard) locks in delivery slot #1.
It’s been a newsworthy week for Aptera Motors and solar EV companies in general. With one fellow SEV startup toiling through a bankruptcy filing and another fighting for its life, our hope in a future of EVs powered by the Sun currently rests heavily on Aptera.
Last Friday, the company’s cofounders Steve Fambro and Chris Anthony held a live streamed webinar, where they walked the public through the specifications of Aptera’s unified, preconfigured Launch Edition solar EV.
The startup’s loyal community was up in arms about the lack of DC charging capability, but it took just three days for the cofounders to take to YouTube once again and quickly makes things right. ALL Aptera solar EVs will now come equipped with DC fast charging, including the Launch Edition. Phew.
While most of last week’s Aptera news was exciting, one discouraging aspect was the fact that deliveries of the Launch Editions remain at least a year away and that the startup needs another $50 million in funding to reach its first gate of scaled production.
Well, the guys at Aptera are back with another video, this time explaining the launch of a new competitive community funding campaign called Accelerate Aptera, complete with a leaderboard.
Aptera’s accelerated funding program starts at $10,000
The company shared details of its new accelerator program in a post to its website this afternoon, which also included a new video from its cofounders you can peep below. First off, Aptera’s team is working through a Series B2 funding round, but says that will take time to secure and finalize.
Aptera has received a $21.9 million grant, but it is all but guaranteed and the process will not be completed until February or March. Furthermore, the grant is a reimbursement, so Aptera must complete eligible purchases (production equipment, machines, etc.) up to $21.9 million with its own money first.
Enter #AccelerateAptera – the company’s latest community funding program intended to put money in the bank and bridge to gap toward prospective grants and series funding rounds. Per the release:
We want to deliver solar mobility to the world as quickly as possible. Our Launch Edition vehicle is only one of many future products we hope to build that will make the world a better place. Once funded, we expect it will be 12 months until production of our first vehicle commences. Without funding, we anticipate our timelines will continue to be pushed back. Our community has always been our biggest asset and we’re asking our order holders and other supporters to now help us to accelerate our growth. If we can raise $20-50 million to execute on the first phase of our production plan, it will help tremendously. We expect our use of proceeds to include capital expenditures such as equipment and tooling and assisting in completing the requirements for obtaining the grant.
Here’s how the accelerated funding program works.
From now through March 26, anyone can invest a minimum of $10,000 in Aptera to join the Launch Edition leaderboard. Investments over $10k qualify you for a $100 coupon (okay?) and a 5% discount on your Aptera solar EV (up to $2,500 and does not include purchase price).
Whoever contributes the highest investment by the end of the funding round will receive the first delivery slot of 2,000 planned Launch Editions. The remaining 1,999 slots will be prioritized down the leaderboard.
Lastly, those reservation holders who already have their hard earned money invested in Aptera will have those amounts added to their leaderboard funding total… as soon as they donate an additional $10,000.
You can join the funding leaderboard by investing here, and can follow the “competition” here. If you still haven’t reserved an Aptera, you can do so here and get $30 off the $100 fee. To learn more about the Accelerate Aptera campaign, see the video below where the cofounders explain it best.
Norway just greenlit this vertical-axis floating wind turbine
Swedish wind turbine maker SeaTwirl got the go-ahead to test its 1 megawatt (MW) S2X vertical-axis floating offshore prototype in Norway.
Vertical-axis floating wind turbine pilot
In March 2022, Norway’s Ministry of Energy gave approval to SeaTwirl and Norwegian offshore wind test center Marine Energy Test Centre to pilot the vertical-axis floating wind prototype for five years at a former fish farm in Boknafjorden, northeast of Lauplandsholmenoff, 700 meters (2,297 feet) from the coast.
But four groups – the Norwegian Environmental Protection Association, the Norwegian Fishermen’s Association, and two campaign groups – appealed against SeaTwirl’s permit, and so the project was put on ice.
Yesterday, the Norwegian Water Resources and Energy Directorate rejected the appeal, so SeaTwirl’s S2X pilot can now proceed, and no further appeals will be considered.
CEO Peter Laurits said:
Our main focus is the commercialization of large turbines, SX, in floating wind farms. The outcome provides freedom to choose and plan the installation of S2x in the way that best supports that goal.
How S2X works
SeaTwirl says that “multiple S2xs can be placed in a dense pattern for increased output.” The company’s reasoning for building vertical (instead of horizontal) axis floating turbines is this:
The simplicity of the design and low center of gravity are the big advantages. All moving parts and electrical systems are easily accessible [and] close to the water’s surface, lowering maintenance costs.
The S2X prototype is 55 meters (180 feet) above sea level, and it’s around 80 meters (262 feet) below sea level. The turbine diameter is 50 meters (164 feet). Its rotor blade height is around 40 meters (131 feet). Its optimal operating depth is 100 meters (328 feet) and deeper.
SeaTwirl isn’t the only company testing vertical-axis wind turbines off the Norwegian coast – earlier this month, aluminum and energy giant Hydro and floating wind specialist World Wide Wind announced that they’re going to test a vertical-axis wind turbine made out of aluminum.
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Audi hints at luxury electric 4×4 to compete with Mercedes Benz and Land Rover
The luxury electric 4×4 you’ve been waiting for is set to emerge in 2027, and no, it’s not the Mercedes Benz G-Class or Land Rover Defender. It’s a new secret project from Audi.
A luxury electric Audi 4×4 coming in 2027
In a first from Audi, the German automaker is showing interest in the luxury 4×4 segment. The secret new electric SUV will feature a top-notch interior with the ability to perform its best on and off the road.
Audi unveiled its new activesphere concept Thursday, a four-door crossover coupe that doubles as a truck. The concept combines a luxury SUV, sports car, and off-roading pickup into one versatile EV.
Although this is a separate concept from the planned electric Audi 4×4, the off-road EV gives us an impression of where the automaker is headed.
In an interview with Autocar, Audi’s head of design, Marc Lichte, hinted at the idea of a new 4×4, saying:
I think there is space [for a rugged SUV in Audi’s lineup]. There is potential because there are only two premium players, and I think there is space for a third one.
Lichte didn’t give up details other than mentioning it will ride on one of Volkswagen’s platforms other than the Audi-Porshce co-developed PPE platform like the activesphere concept.
Since Volkswagen’s next-gen SSP platform designed for all segments has been delayed until at least 2028, there’s a good chance Audi’s new 4×4 will share technology with VW’s recently revived Scout off-road brand of vehicles.
Following Volkswagen’s announcement last year that it would revive the Scout brand for an all-electric lineup and bring rugged SUVs to the United States, reports surfaced VW was considering Canadian parts manufacturer Magna (which also builds the Mercedes Benz G-Class) to help build the vehicles.
The initial plans called for Audi to build Scout models in a new US facility but were later scrapped. According to Autocar, the two brands may still benefit from each other.
Audi is already working with Magna to develop electric vehicle batteries for the Scout brand. With VW reportedly leaning toward having the part supplier build 100,000 Scout EVs, there could be room for an additional 50,000 electric Audi 4×4 models to be built alongside.
Audi is already familiar with electric off-road technology with its beastly RS Q e-tron rally car (and Quattro four-wheel drive tech) and is well known for its premium luxury interior. It seems like a match made in heaven to me.
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