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.
Taiwanese smart-scooter pioneer Gogoro is taking a step into more accessible territory with its newest model, the Ezzy. The company hopes to leverage its massive lead in battery-swapping technology while also bringing its smart scooters to a broader audience by lowering its price point.
Designed as a no-frills, budget-friendly ride that doesn’t skimp on modern conveniences, Ezzy is priced around NT$59,980 (around US $2,000). Once you add in the government subsidies from its native Taiwan, that price drops below NT$30,000 (around US $1,000). For Gogoro, this is the smartscooter distilled to its essential core: practical, connected, and ready for daily life.
The Ezzy looks like it is trying to build on Gogoro’s success with its 2024 Jego launch, the company’s previous forray into lower cost electric scooters. The Jego was a massive success and wound up resulting in around 40% of the company’s sales. Now the Ezzy looks to keep the good vibes rolling in a sleek, compact, and intuitive package.
The scooter features a rounded, minimalist body with a durable front panel and straightforward controls. Practicality is the guiding principle: a 68 cm (27 inch) long seat, spacious footwell, and a 28 liter (7.4 gallon) under-seat storage compartment, which the company says is large enough for two helmets – if they’re a 3/4 and a half helmet. Put it all together, and the features sound like they should make the Ezzy ideal for urban errands or weekend jaunts. Add in a built-in cupholder and flip-out footrests, and you’ve got a scooter designed to seamlessly slot into everyday routines with one or two riders aboard.
The design is cute, but it’s under the panels where Gogoro usually tries to set itself apart. Ezzy is powered by a new hub motor capable of speeds up to 68 km/h (42 mph), high enough for city traffic while keeping maintenance low. The last time I was scootering around in Taipei, those speeds felt like plenty on the congested streets.
And while Gogoro’s scooters have long been impressive, the most important part of the company’s offerings isn’t even its rides, it’s how they’re powered. Ezzy integrates directly into Gogoro’s famed battery-swapping network, which includes thousands of swap stations around Taiwan.
Riders can skip charging downtime by swapping depleted packs at GoStation kiosks, which regularly see hundreds of thousands of battery swaps every day.
Electrek’s Take
In terms of performance, Ezzy strikes a balance. It’s not built for speed demons, but it likely won’t bog down in traffic either. It’s not overflowing with gadgets, yet includes thoughtful features that matter – cup holder, flip-out footrests, and room for two helmets. At around US $2,000 retail before subsidies, it’s clearly aimed at broadening access to smart two-wheeling in dense cities. And since the combustion engine scooters still dominate cities in most countries, making electric alternatives more affordable is a key part of displacing those heavy polluters.
This feels less like a normal launch and more like a strategic pivot for Gogoro. While the company’s premium Smartscooters – like the sports car-inspired Pulse or high-performance SuperSport – are impressive, they’re also spendy and niche. Ezzy, by contrast, looks like what Gogoro might want every city overpopulated by cars to embrace: a stylish, comfortable, and economical electric scooter that’s accessible to the masses.
It’s still early days and Gogoro hasn’t confirmed availability beyond Taiwan, but enthusiasm for affordable, swappable-battery electric scooters is growing. If Ezzy finds even moderate success in its initial market, it could pave the way for Gogoro to expand its smart ecosystem deeper into urban centers worldwide.
In short, Ezzy may not be a headline-grabbing performance machine, but that’s exactly the point. Sometimes progress happens not with fireworks, but with smart, thoughtful moves that make electric mobility more attainable for everyone. And that’s an evolution worth riding along with.
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The e-bike industry in the West has long been a tale of two territories. North Americans enjoy higher speeds and power limits for their electric bicycles while Europeans are held to much stricter (i.e. slower and lower) speed and power limits. However, things might change based on current discussions on rewriting European e-bike regulations.
New power levels are not totally without precedent, either. The UK briefly considered doubling its own e-bike power limit from 250 watts (approximately 1/3 horsepower) to 500 watts, though the move was ultimately abandoned.
But this time, the call for more power is coming from within the house – i.e., Germany. The Germans are the undisputed leaders and trend setters in the European e-bike market, accounting for around two million sales of e-bikes per year. Home to leading e-bike drive makers like Bosch, the country has yet another advantage when it comes to making – or regulating – waves in the industry.
And while there aren’t any pending law changes, the largest German trade organization ZIV (Zweirad-Industrie-Verband), which is highly influential in achieving such changes, is now discussing what it believes could be pertinent updates to current EU electric bike regulations.
Some of the new regulations involve creating rules maxing out power at levels such as 400% or 600% of the human pedaling input. But a key component of the proposed plan includes changing the present day power limit of e-bikes from 250W of continuous power at the motor to 750W of peak power at the drive wheel.
The difference includes some nuance, since continuous power is often considered more of a nominal figure, meaning nearly every e-bike motor in Europe wears a “250W” or less sticker despite often outputting a higher level of peak power. Even Bosch, which has to walk the tight and narrow as a leader in the European e-bike drive market, shared that its newest models of motors are capable of peak power ratings in the 600W level. That’s still far from the commonly 1,000W to 1,300W peak power seen in US e-bike motors, but offers a nice boost over an actual 250W motor.
Other new regulations up for discussion include proposals to limit fully-loaded cargo e-bike weights to either 250 kg (550 lb) for two-wheelers or 300 kg (660 lb) for e-bikes with more than two wheels. As road.cc explained, ZIV also noted that, “separate framework conditions and parameters must be defined for cargo bikes weighing more than 300 kg (see EN 17860-4:2025) as they differ significantly from EPACs and bicycles in their dynamics, design and operation.” Such heavy-duty cargo e-bikes, which often more closely resemble small delivery vans than large cargo bikes, are becoming more common in the industry and have raised concerns about cargo e-bike bloat, especially in dedicated cycling paths.
It’s too early to say whether European e-bike regulations will actually change, but the fact that key industry voices with the power to influence policy are openly advocating for it suggests that new rules for the European market are a real possibility.
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China just laid out a plan to roll out over 100,000 ultra-fast EV charging stations by 2027 – and they’ll all be open to the public.
The National Development and Reform Commission’s (NDRC) joint notice, issued on Monday, asks local authorities to put together construction plans for highway service areas and prioritize the ones that see 40% or more usage during holiday travel rushes.
The NDRC notes that China’s ultra-fast EV charging infrastructure needs upgrading as more 800V EVs hit the road. Those high-voltage platforms can handle super-fast charging in as little as 10 to 30 minutes, but only if the charging hardware is up to speed.
China had 31.4 million EVs on the road at the end of 2024 – nearly 9% of the country’s total vehicle fleet. But charging access is still catching up. As of May 2025, there were 14.4 million charging points, or roughly 1 for every 2.2 EVs.
To keep the grid running smoothly, China wants new chargers to be smart, with dynamic pricing to incentivize off-peak charging and solar and storage to power the charging stations.
To make the business side work, the government is pushing for 10-year leases for charging station operators, and it’s backing the buildout with local government bonds.
The NDRC emphasized that the DC fast chargers built will be open to the public. This is a big deal because a lot of fast chargers in China aren’t. For example, BYD’s new megawatt chargers aren’t open to third-party vehicles.
As of September 2024, China had expanded its charging infrastructure to 11.4 million EV chargers, but only 3.3 million were public.
Read more: California now has nearly 50% more EV chargers than gas nozzles
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