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.
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The UAW has launched an unprecedented campaign to unionize the entire US auto sector at once, with thousands of auto workers at 13 companies announcing simultaneous unionization campaigns.
After UAW’s big strike win, winning 25%+ pay increases at the “Big Three” American automakers after a simultaneous strike at GM, Ford and Stellantis, the union is looking to maintain that momentum and go bigger.
Immediately after declaring victory, UAW President Shawn Fain said that in the next negotiation in 2028, UAW wants to come back to the bargaining table to negotiate not just with the Big Three, but with “a Big Five or a Big Six” – implying that the union planned to expand to other automakers. And President Biden said that he would support a UAW push to unionize Tesla and Toyota.
Now we’ve seen an official announcement that UAW isn’t just looking to unionize two or three more automakers, but all of them at once. Typically, unionization campaigns focus on a single company at a time, but here UAW is targeting a whole sector with simultaneous campaigns at each individual company. This seems like a tall order, but UAW’s triple-strike against the Big Three seemed to work out well, so it’s now applying that simultaneous tactic to organizing new union drives.
In service of its goal, UAW launched a new website at uaw.org/join, asking workers at each company to sign their union card. The website mentions several automakers by name, and has links to individual campaigns for each automaker where workers can go to express their interest in unionizing:
The campaign was accompanies by a video narrated by Fain making his union pitch. In short, UAW says that automakers and investors are making record profits, but that worker compensation has not kept up. The video specifically mentions Tesla and Rivian’s recent quarterly results, and also states that the Japanese/Korean automakers have combined to make $470 billion in profits, and the German automakers have made an additional $460 billion, in the last ten years.
Since the UAW’s big wins, other automakers have moved to increase pay to (partially) keep up with pay increases at the Big Three. VW, Hyundai, Toyota and Honda have all announced hikes in pay, showing how union wins can buoy an entire industry by making automakers compete for workers with higher pay.
But UAW doesn’t want to stop at a few voluntary pay hikes from other companies, it thinks that unionizing those companies can give workers a better deal. One worker at Toyota’s Georgetown, Kentucky plant put it thusly:
We’ve lost so much since I started here, and the raise won’t make up for that. It won’t make up for the health benefits we’ve lost, it won’t make up for the wear and tear on our bodies. We still build a quality vehicle. People take pride in that, but morale is at an all-time low. They can give you a raise today and jack up your health benefits tomorrow. A union contract is the only way to win what’s fair.
Jeff Allen, 29-year Toyota assembly worker
UAW also quoted workers at Hyundai, VW, Mercedes and Rivian in its release, focusing on how they think unionization would improve safety and benefits at these automakers.
Electrek’s Take
Unions are having a bit of a moment in the US, reaching their highest popularity ever since surveys started asking about them.
Much of union popularity has been driven by COVID-related disruptions across the economy, with workers becoming unsatisfied due to mistreatment (labeling everyone “essential,” companies ending work-from-home) and with the labor market getting tighter with over 1 million Americans dead from the virus and another 2-4 million (and counting) out of work due to long COVID.
Unions have seized on this dissatisfaction to build momentum in the labor movement, with successful strikes across many industries and organizers starting to organize workforces that had previously been nonunion.
But union membership has been down over several decades in the US, and as a result, pay hasn’t kept pace with worker productivity and income distribution has become more unequal over time. It’s really not hard to see this influence when you plot these trends against each other.
It’s quite clear that lower union membership has resulted in lower inflation-adjusted compensation for workers, even as productivity has skyrocketed. As workers have produced more and more value for their companies, those earnings have gone more and more to their bosses rather than to the workers who produce that value. And it all began in the 80s, around the time of Reagan – a timeline that should be familiar to those who study social ills in America.
All of this isn’t just true in the US but also internationally. If you look at other countries with high levels of labor organization, they tend to have more fair wealth distribution across the economy and more ability for workers to get their fair share.
We’re seeing this in Sweden right now, as Tesla workers are striking for better conditions. Since Sweden has 90% collective bargaining coverage, it tends to have a happy and well-paid workforce, and it seems clear that these two things are correlated. And while that strike is continuing, meaning we haven’t yet seen the end of it, most observers think that the workers will eventually get what they want since collective bargaining is so strong in that country.
These are all reasons why, as I’ve mentioned in many of these UAW-related articles, I’m pro-union. And I think everyone should be – it only makes sense that people should have their interests collectively represented and that people should be able to join together to support each other and exercise their power collectively instead of individually.
This is precisely what companies do with industry organizations, lobby organizations, chambers of commerce, and so on. And it’s what people do when sorting themselves into local, state, or national governments. So naturally, workers should do the same. It’s just fair.
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The Rivian R1T might get an exciting upgrade. The electric pickup can drive through 3+ feet of water, rock crawl a 100% grade, and take off like a sports car. But what if the Rivian R1T had a mobile projector that could be easily stored in the gear tunnel? That’s what Rivian is scheming up.
Rivian files patent for R1T mobile movie projector
Rivian’s R1T electric truck is the ultimate adventure vehicle. It recently made history as the first EV to win the off-road Rebelle rally, the longest of its kind in the US.
The truck continues improving through OTA updates that add fun new features, range, and more. One of its most recent improved the ride quality of its vehicles. By building its cars from the ground up, Rivian has a major advantage.
Like Tesla, the EV maker focused on software and “having the ability to configure every piece of hardware,” according to Wassym Bensaid, Rivian’s VP of software development.
Rivian can use this advantage to create unique products that integrate into its EVs. One of its most recent ideas is a mobile projector.
According to a new patent filing for a “vehicle entertainment apparatus,” the Rivian R1T could soon see an added movie projector.
The patent, filed November 23, details a kit that can include a projector, screen, and at least one speaker. The kit is attached to a shuttle that slides in and out of the gear tunnel for easy storage.
Once extended, the projector can be rotated into position. It will also include a mirror to reflect the projected light onto the screen without harming quality. Meanwhile, the pole to hold the screen will fit into several spots.
The setup enables a mobile entertainment setup in little to no time. Everything can be stored in the gear tunnel while not in use. When ready, it can just slide out and set up.
Rivian is including everything needed for the ultimate movie night on the go. And the best part – everything is powered by the R1T.
Electrek’s Take
Although a movie projector may seem like a wild idea to some, that’s right up Rivian’s alley. The company has developed several add-on options like a three-person tent and the Camp Kitchen.
Many were dissapointed when Rivian discontinued the Camp Kitchen from its gear shop earlier this year. The $5,000 add-on included a pull-out kitchen complete with two induction cooktops, a water tank, collapsable sink, and more.
Rivian CEO RJ Scaringe said on the MKBHD podcast that the idea was more popular than expected. However, Rivian is redesigning it for something that doesn’t take up the entire gear tunnel.
Maybe a Rivian R1T movie projector isn’t that far off after all. Meanwhile, Rivian will likely offer a redesigned camp kitchen first.
Would you consider buying Rivian’s movie projector add-on? Let us know what you think in the comments.
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