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.
A new bill introduced Friday by US Senator Angus King of Maine could unlock the true potential of electric school buses and provide stability to communities in need. The BIDIRECTIONAL Act would “create a program dedicated to deploying electric school buses with bidirectional vehicle-to-grid (V2G) flow capability.”
Zero-emission electric school buses are being deployed nationwide as state leaders and school districts look to protect the children and communities they vow to serve. New information shows school districts that replace just one diesel school bus with an electric one can reduce toxic emissions by 54,000 pounds a year.
However, the benefits of electric school buses don’t stop there. The massive batteries they utilize also make perfect energy storage devices. Several automakers and charging companies are experimenting with vehicle-to-grid (V2G) technology that enables vehicles to send energy back to the grid.
Manufacturers of electric pickup trucks (like the Ford F-150) and other EVs have dived into bi-directional charging, but this technology makes even more sense for electric school buses because they have large batteries that sit most of the day. To illustrate this point, Thomas Built Buses partnered with Proterra to show two electric school buses can send 10 MWh total back to the grid, enough to power around 600 homes.
Senator King wants to capitalize on this ability with the BIDIRECTIONAL Act to promote the widespread deployment of electric school buses with V2G capability to improve community stability.
The BIDIRECTIONAL Act is designed to accelerate adoption of EV school buses while using them for more than just a ride to school.
According to Senator King, the BIDIRECTIONAL Act will:
- Establish a Department of Energy (DOE) program to roll out electric school buses designed with V2G capabilities in communities that need them most.
- Require the DOE to report on current V2G initiatives (such as Thomas Built and Proterra) while also requiring electricity providers to consider bi-directional integration.
Senator King commented on the initiative, stating:
Vehicle-to-grid school buses are another common sense tool that can help to create a reliable grid, promote clean energy, and cut costs for local towns and school districts.
Adding:
The BIDIRECTIONAL Act will assist school districts across Maine and America transition to electric buses and make sure these vehicles provide greater stability to their communities. Combined with electric bus investments in the Inflation Reduction Act, this will be an important step towards unlocking America’s clean energy future. It’s a simple, win-win bill and I hope it can get bipartisan support across Congress.
Several major electric school bus makers and other organizations are backing the bill, such as Blue Bird, Highland Electric, Lion Electric, Nuuve, Proterra, and Xcel Energy.
Electrek’s Take
Electric school buses with V2G are a no-brainer. Not only will they reduce greenhouse gas emissions, protecting the communities they serve, but they can also play a key role in providing energy stability to communities in need.
The Environmental Protection Agency (EPA) just announced it would be nearly doubling EPA clean school bus program funding to $965 million in its initial round . Federal funding is a huge first step, but strong state leadership is also necessary if these clean machines are going to become widely adopted. Virginia, for example, just surpassed 500,000 electric school bus miles driven thanks to a state initiative to roll out 13,0000 electric school buses in 2019. They now have the nation’s second largest fleet of electric school buses.
I believe Senator King is wise in proposing this bill. I truly believe electric school buses have unlimited potential waiting to be unlocked, and the BIDIRECTIONAL Act can do just that.
FTC: We use income earning auto affiliate links. More.
Subscribe to Electrek on YouTube for exclusive videos and subscribe to the podcast.
The Environmental Protection Agency (EPA) announced Thursday that the agency will almost double its funding for electric school buses to close to $1 billion after school districts from all 50 states applied for rebates.
Electric school buses are quickly taking over streets around the US as school districts and state leaders see how they can benefit the communities they serve in.
According to Dominion Energy, a power provider promoting the use of EVs for a cleaner and sustainable future, replacing one diesel bus can reduce greenhouse gas emissions by 54,000 pounds annually.
With help from Dominion’s initiatives, the second largest electric bus fleet in the US just crossed 500,000 service miles. By implementing EV buses, Virginia school districts were able to avoid 447.7 short tons of greenhouse gases.
These toxic fumes are known to creep into the bus’s interior while the bus is idling, harming the health of students taking them every day. A 2002 Yale study found dangerous particle levels were five to ten times higher while buses were stopped.
Although new standards have come along since then, it’s still not enough to limit the exposure when you can cut it out altogether.
Not only do electric school buses produce zero emissions, but they can also save school districts money on fuel and repair costs in the long run. For example, The Modesto Unified School District in California, which ordered 30 Blue Bird EV school buses, expects to save $250,000 a year on fuel.
With federal and many state funding options, there’s never been a better time to convert to an all-electric school bus fleet.
EPA doubles funding for electric school bus fleets across the US
The EPA Clean School Bus Program, part of the Bipartisan Infrastructure Law, provides $5 billion in funding for electric school buses through the next five years.
The first round of funding, announced in May, was supposed to free up $500 million, but after overwhelming demand from school districts across all 50 states, the EPA will now be almost doubling it to $965 million.
The EPA received about 2,000 applications, amounting to nearly $4 billion in funding, with over 90% submitting for zero-emission electric school buses. Sue Gander, director of the electric school bus initiative at the World Resources Institute, highlights the demand for fully electric options, claiming:
There’s more to the story. The overwhelming demand for electric school buses, over any other fuel type, is striking. Applicants across the country chose electric buses over propane at a rate of 10 to 1. There’s no doubt we’re entering a new, electric era in student transportation, one with massive benefits for our kids’ health, climate and the economy.
With requests for over eight times the initial funding round, EPA Administrator Michael S. Regan said on the program’s success thus far:
America’s school districts delivered this message loud and clear – we must replace older, dirty diesel school buses. Together, we can reduce climate pollution, improve air quality, and reduce the risk of health impacts like asthma for as many as 25 million children who ride the bus every day.
The EPA said it’s “moving swiftly” to review applications and expects the list of winning applicants to be released in October 2022. Applicants will be selected through a lottery-based system.
Another $1 billion round of funding for electric school buses will be in the Fiscal Year 2023, according to the EPA. The agency plans the next funding program to launch in the next few months, including a grant competition.
However, more may need to be done. Senator Carper, chair of the senate committee on environmental and public works, talks about the need for further funding, saying:
Given the response to the availability of these dollars, it’s clear that more funding is needed. I look forward to working with Administrator Regan, the rest of the Biden Administration, and my colleagues in Congress to build on this progress so that more communities can realize the clean air and energy saving benefits of these cleaner vehicles.
Will we have access to more funding for electric school buses? Time will tell. If the initial demand is any indication, school districts are ready and willing. It’s time to get the funding to make it happen.
FTC: We use income earning auto affiliate links. More.
Subscribe to Electrek on YouTube for exclusive videos and subscribe to the podcast.
-
World3 days agoLabour MP Rupa Huq suspended and apologises after calling Chancellor Kwasi Kwarteng ‘superficially’ black
-
US3 days ago‘Take this very seriously’: Florida warned over Hurricane Ian as fuel and food stockpiled
-
Environment3 days agoWatch Eviation’s all-electric Alice aircraft first flight
-
Sports3 days agoIn the heart of Texas, old Southwest Conference rivalries run deep. But for how long?
-
Environment3 days agoWeather the storm with Anker’s 1,024Wh solar power station at $1,600 in New Green Deals
-
Technology3 days ago
A game about sheep is going viral in China even as gaming regulation remains tight
-
Business10 months ago
Deliveroo picks Goldman as broker despite US bank’s role on IPO flop
-
Business3 days agoKwasi Kwarteng to hold meeting with bankers as fallout from mini-budget continues