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.
Mining company Vale is turning to Caterpillar to provide this massive, 240-ton battery-electric haul truck in a bid to slash carbon emissions at its mines by 2030.
Caterpillar and Vale have signed an agreement that will see the Brazilian mining company test severe-duty battery electric mining trucks like the 793 BEV (above), as well as V2G/V2x energy transfer systems and alcohol-powered trucks. The test will help Vale make better equipment choices as it works to achieve its goals of reducing direct and indirect carbon emissions 33% by 2030 and eliminating 100% of its net emissions by 2050.
If that sounds weird, consider that most cars and trucks in Brazil run on either pure ethyl alcohol/ethanol (E100) or “gasohol” (E25).
“We are developing a portfolio of options to decarbonize Vale’s operations, including electrification and the use of alternative fuels in the mines. The most viable solutions will be adopted,” explains Ludmila Nascimento, energy and decarbonization director Vale. “We believe that ethanol has great potential to contribute to the 2030 target because it is a fuel that has already been adopted on a large scale in Brazil, with an established supply network, and which requires an active partnership with manufacturers. We stand together to support them in this goal.”
Vale will test a 240-ton Cat 793 battery-electric haul truck at its operations in Minas Gerais, and put energy transfer solutions to a similar tests at Vale’s operations in Pará over the next two-three years. Caterpillar and Vale have also agreed to a joint study on the viability of a dual-fuel (ethanol/diesel) solution for existing ICE-powered assets.
Vale claims to be the world’s largest producer of iron ore and nickel, and says it’s committed to an investment of between $4 billion to $6 billion to meet its 2030 goal.
Cat 793 electric haul truck
During its debut in 2022, the Cat 793 haul truck was shown on a 4.3-mile test course at the company’s Tucson proving grounds. There, the 240-ton truck was able to achieve a top speed of over 37 mph (60 km/h) fully loaded. Further tests involved the loaded truck climbing a 10% grade for a full kilometer miles at 7.5 mph before unloading and turning around for the descent, using regenerative braking to put energy back into the battery on the way down.
Despite not giving out detailed specs, Caterpillar reps reported that the 793 still had enough charge in its batteries for to complete more testing cycles.
Electrek’s Take
Electric equipment and mining to together like peanut butter and jelly. In confined spaces, the carbon emissions and ear-splitting noise of conventional mining equipment can create dangerous circumstances for miners and operators, and that can lead to injury or long-term disability that’s just going to exacerbate a mining operation’s ability to keep people working and minerals coming out of the ground.
By working with companies like Vale to prove that forward-looking electric equipment can do the job as well as well as (if not better than) their internal combustion counterparts, Caterpillar will go a long way towards converting the ICE faithful.
SOURCES | IMAGES: Caterpillar, Construction Equipment, and E&MJ.
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American mine; via NPROXX
Argonne National Laboratory is building a new research and development facility to independently test large-scale hydrogen fuel cell systems for heavy-duty and off-road applications with funding from the US Department of Energy.
The US Department of Energy (DOE) is hoping Argonne Nat’l Lab’s extensive fuel cell research experience, which dates back to 1996, will give it unique insights as it evaluates new polymer electrolyte membrane (PEM) fuel cell systems ranging from 150 to 600 kilowatts for use in industrial vehicle and stationary power generation applications.
The new Argonne test facility will help prove (or, it should be said, disprove) the validity of hydrogen as a viable fuel for transportation applications including heavy trucks, railroad locomotives, marine vessels, and heavy machines used in the agriculture, construction, and mining industries.
“The facility will serve as a national resource for analysis and testing of heavy-duty fuel cell systems for developers, technology integrators and end-users in heavy-duty transportation applications including [OTR] trucks, railroad locomotives, marine vessels, aircraft and vehicles used in the agriculture, construction and mining industries,” explains Ted Krause, laboratory relationship manager for Argonne’s hydrogen and fuel cell programs. “The testing infrastructure will help advance fuel cell performance and pave the way toward integrating the technology into all of these transportation applications.”
The Hydrogen and Fuel Cell Technologies Office (HFTO) of DOE’s Office of Energy Efficiency and Renewable Energy is dedicating about $4 million to help build the new Argonne facility, which is set to come online next fall.
Electrek’s Take
It’s going to be hard to convince me that the concentrated push for a technology as inefficient as hydrogen fuel cells has more to do with any real consumer or climate benefit than it does keeping the throngs of people it will take to manufacture, capture, transport, store, house, and effectively dispense hydrogen gainfully employed through the next election cycle.
As such, while case studies like the hydrogen combustion-powered heavy trucks that have been trialed at Anglo American’s Mogalakwena mine since 2021 (at top) and fuel cell-powered concepts like Komatsu’s medium-sized excavator (above) have proven that hydrogen as a fuel can definitely work on a job site level while producing far fewer harmful emissions than diesel, I think swappable batteries like the ones being shown off by Moog Construction and Firstgreen have a far brighter future.
Speaking of Moog, we talked to some of the engineers being their ZQuip modular battery systems on a HEP-isode of The Heavy Equipment Podcast a few months back. I’ve included it, below, in case that’s something you’d like to check out.
SOURCES | IMAGES: ANL, Komatsu, and NPROXX.
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Velocity truck rental is doing its part to help commercial fleets electrify by energizing 47 high-powered charging stations at four strategic dealer locations across Southern California. And they’re doing it now.
The new Velocity Truck Rental & Leasing (VTRL) charging network isn’t some far-off goal being announced for PR purposes. The company says its new chargers are already in the ground, and set to be fully online and energized by the end of this month at at VTRL facilities in Rancho Dominguez (17), Fontana (14), the City of Industry (14), and San Diego (2).
45 120 kW Detroit e-Fill chargers make up the bulk of VTRL’s infrastructure project, while two DCFC stations from ChargePoint get them to 47. All of the chargers, however, where chosen specifically to cater to the needs of medium and heavy-duty battery electric work trucks.
The company says it chose the Detroit e-Fill commercial-grade chargers because they’ve already proven themselves in Daimler-heavy fleets with their ability to bring Class 8 Freightliner eCascadias, Class 6 and 7 Freightliner eM2 box trucks, and RIZON Class 4 and 5 cabover trucks, “to 80% state of charge in just 90 minutes or less.”
At Velocity, we are not just reacting to the shift towards electric mobility; we are at the forefront with our customers and actively shaping it. By integrating high-powered, commercial-grade charging solutions along key transit corridors, we are ensuring that our customers have the support they need today. This charging infrastructure investment is a testament to our commitment to helping our customers transition smoothly to electromobility solutions and to prepare for compliance with the Advanced Clean Fleets (ACF) regulations.
David Deon, velocity president
Velocity plans to offer flexible charging options to accommodate the needs of different fleets, including both managed, “charging as a service” subscription plans and self-managed/opportunity charging during daily routes. While trucks are charging, drivers and operators will be able to relax in comfortable break rooms equipped with WIFI, television, snacks, water, and restrooms.
Electrek’s Take
While it feels a bit underwhelming to write about trucking companies simply following the letter of the law in California, the rollout of an all-electric, zero-emission commercial trucking fleet remains something that, I think, should be celebrated.
As such, I’m celebrating it. I hope you are, too.
SOURCE | IMAGES: Global Newswire; Daimler Trucks.
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