Expert Talk: Developing Solar for New Frontiers: From Flexible Cells to Scalable Production

Key takeaways

• CIGS on ultra-thin glass enables flexible, lightweight (tandem) solar cells ideal for emerging markets like vehicles, aerospace, and wearable tech.
• Scaling from lab to industry sizes required redesigning processes and cross-border collaboration.
• Material choice matters: a package based on UTG can offer even lower module weight compared to one based on stainless steel foils.
• Next-gen research targets WSe2 solar cells with all plastic packaging, aiming at maximum flexibility, minimum weight, and a 3 kW/kg power-to-weight ratio — over three times current space-grade tech.

“Conventional solar panels are either too heavy, too rigid, too expensive, or not resilient enough for many emerging applications,” says Hamtaei. “But if we rethink the materials and manufacturing processes behind them, we can unlock a completely new category of energy solutions.”

Hamtaei’s PhD research explores how to do exactly that — using CIGS (copper indium gallium selenide) thin-film solar technology on ultra-thin glass (UTG) substrates, scaling from lab-size prototypes to more industry appropriate dimensions. Alongside this, he’s preparing a next step: introducing advanced materials like transition metal dichalcogenides (TMD) like tungsten diselenide (WSe2) to push solar cells beyond their current limits in both efficiency and module weight reduction.

For industry players looking to future-proof their energy systems — or create entirely new solar-powered products — his findings carry both technical insight and strategic relevance.

The Shift: New Use Cases, New Requirements

The solar industry is no longer defined solely by rooftops and solar farms. A growing number of sectors are calling for energy solutions that go where current solutions are either too heavy (and suboptimal) or too expensive (and logistically volatile) — aerospace, transport, wearables, and building skins among them. In all these cases, light weight, flexibility, and scalability aren’t extras — they’re definitely the baseline.

“In aerospace, every kilogram counts,” says Hamtaei. “If you reduce the panel weight from for example 10 kg to 1 kg, that’s payload that can now go to sensors, instruments, or fuel efficiency. And if the panels are flexible, you can fold or roll them (called stowability), making transport, and installation and deployment far more efficient.”

Traditional PV modules — typically made of thick glass and metal frames — are too heavy, brittle, and static for these new environments (with the recent and remarkable exception of Solestial). They lack adaptability, integration versatility, and in some cases, safety. Think of vehicle integrated panels shattering upon impact, for example.

That’s where flexible thin-film technologies come in handy. CIGS has already proven itself as a mature, high-efficiency thin-film material. In addition, it is known to be a more reliable, stable material compared to some alternatives, like perovskites or organics. Taking the example of aerospace again, thin-film PV is much more affordable, and reliable from a supply chain perspective, compared to incumbent III-V option, and much more resilient from a space-stressor point of view, compared to Si.

Scaling Challenges: From Lab to Fab

Hamtaei’s research is in that line: using ultra-thin (<200 μm) glass substrates to create CIGS solar cells that are not only bendable, but also highly uniform and durable, while using industrially viable methodologies. But designing a flexible solar cell in a lab is one thing. Producing it in a large-area is a different challenge.

In his PhD, Hamtaei tackled this transition head-on. Most laboratory solar cells are fabricated on small 5×5 cm substrates, but the industry standard sits at 6-inch wafers (150 mm) — a nearly tenfold increase in area. Though that also differs per sector. Again, with aerospace, a half cut is usually used.

“That leap in size isn’t trivial,” he explains. “Many lab tools simply aren’t built to handle large substrates. We often had to ship samples between partner labs across borders to complete different fabrication steps. It’s been a logistical puzzle, for sure.”

Throughout his PhD, Hamtaei navigated this by working across labs and institutions to get each part of the process done right.

This patchwork approach reflects the reality of scaling niche technology without a turnkey production line. Institutions like TNO in the Netherlands provided access to large-area deposition tools, while other partners like Corning have supplied ultra-thin glass substrates — essential for Hamtaei’s focus on weight reduction and mechanical flexibility. On the other hand, the University of Luxembourg helped with a crucial process step in CIGS processing, leveraging their near-zero waste technique to grow high quality, and environmentally friendly buffer layer material (In2S3).

Beyond tooling, the shift to ultra-thin glass — from conventional 3 mm to just 100 microns thick — demanded a full rethinking of the process. Unlike rigid substrates, thin glass can bend and flex, but it also requires:

• New deposition methods that avoid warping or breakage
• Conformal barrier layers to prevent contamination and diffusion
• Recalibrated heating and handling protocols to manage thermal and mechanical stress

Crucially, this was not about copying existing processes onto larger sheets. 

“We didn’t just change the sample size — we had to redesign the process,” says Hamtaei.

“The process which we had to re-design and optimize had more than 20 different parameters. When you think of these parameters as knobs on a tool, which you turn and then the outcome is different, then that means the possibilities to change were immense. We didn’t run all those possibilities, but you get the picture.”

Technical Differentiation: Choosing the Right Materials and Methods

While flexible solar cells are gaining traction in research, not all approaches are equally suited for real-world application. Sarallah Hamtaei’s work stands out not only for what it builds — but for how it’s built, and the reasoning behind each technical choice.

The core technology in his research is CIGS (copper indium gallium selenide) — a thin-film photovoltaic material known for its high efficiency, long-term stability, and industrial maturity. But what makes his approach stand out further, is the synthesis tools he uses in his research, and his choice of substrate: ultra-thin glass, as opposed to the more commonly used metal foils like stainless steel.

The reason? During the high-temperature synthesis required for CIGS, impurities from stainless steel can diffuse into the CIGS absorber layer, creating performance-degrading defects — a challenge many labs and industry players have encountered. Some companies, such as EnFoil, Midsummer, and Miasole, have developed workarounds to this problem. Others are exploring alternative metal foils like titanium, which holds strong promise for space applications due to its favourable properties. Besides, eventual packaging based on UTG could result in overall lower weight. In fact, the only packaging technology capable of beating UTG in terms of weight is all-plastic, which brings its own challenges.  

Hamtaei’s research aligns with this effort but takes a different path: using ultra-thin glass to ensure uniformly high carrier lifetime across CIGS absorber and the absence of contamination issues — essential for industrial-grade performance.

Future Roadmap & Market Fit

While much of Hamtaei’s work focused on bringing ultra-thin glass-based solar modules to industrial scale, the next leap is already on the horizon: “In a collaboration with Stanford University and NREL, we developed and evaluated WSe2 photovoltaic absorbers on polyimide foils.” This marks a shift on two fronts; one towards simple, yet highly promising material structures in transition metal dichalcogenides (TMD), and one to even lighter, more adaptable substrate materials in plastic foils— potentially unlocking even more applications, such as wearables, where weight and flexibility are non-negotiable. 

“Some of the challenges were as much as scientific, as logistical,” he explains. “For 6-inch synthesis of these materials, we couldn’t do everything in one place, and we had to pull both sides’ expertise — so we had to move samples between labs and countries to get the processing steps aligned and optimized.”

The goal? Even lighter, more flexible modules with projected specific power values of 3 kW/kg — more than triple today’s space-grade solar tech, and at a fraction of the price point. This opens new frontiers where every gram counts: satellites, drones, wearables, and even short-haul electric aircrafts.

But real-world adoption will depend on more than technical performance.

Market fit also means: 

• Compatibility with existing (semiconductor) manufacturing ecosystem and roadmap. Silicon has proven to be a great solar technology, and has been successful in addressing many hurdles on its way. Part of that success comes from the fact that silicon is also the backbone of the semiconductor industry. This means both tools and scientific insight could be shared between the communities. A similar synergistic scenario is ideal for the next generation of solar technologies. TMDs are great from that perspective.
• Demonstrated durability and reliability under combined, real-life conditions. This means that while isolated stress tests reveal a lot of information about material and device behaviour, it is crucially important to analyze cells and modules under combined stressors, and most ideally, in in-operando conditions. 

To further develop such technologies, Hamtaei is now preparing a follow-up project that builds on the monolithic, large-area synthesis of TMD solar cells. Early work has shown these films can be deposited uniformly on 6-inch wafers in under two hours, making the process attractive not only for labs but for future pilot-scale production. “We now need to focus on fabricating the full solar cell device, and assess material/device quality under multiple stressors, which brings its own challenges. For instance, in another study with Argonne lab and Stanford, we showed outstanding resilience of ALD grown MoS2 photovoltaic absorbers under proton radiation. This is very promising, and needs to be complemented with more reliability testing, and ideally combined (operando) studies.” 

“There’s still a gap between what works in a cleanroom and what fits into a commercial supply chain,” Hamtaei notes. “But the interest is growing. The more we work with real use cases, the more likely we are to land technology that matters, form partnerships and get funding.”

Bridging Innovation and Industry

For Hamtaei, flexible solar technology isn’t just a research ambition — it’s a call to reimagine where and how we generate power.

The breakthroughs in this PhD point to a future where solar panels are no longer confined to rooftops and fields, but embedded into vehicles, building skins, drones, and beyond. But to get there, he says, aligning with industry is essential — not just for scaling production, but for aligning innovation with actual needs.

“Engineering solutions are only useful if they solve the right problem,” he says. “That means we need real input from application developers, manufacturers, and system integrators — people who know the constraints and performance requirements in their sector.”

As the solar landscape expands into mobility, aerospace, and infrastructure, Hamtaei sees EnergyVille as a key link between academic excellence and industrial readiness.

He also points to silicon as a benchmark for what successful solar innovation looks like. Its durability, efficiency, and compatibility with the semiconductor industry helped it scale globally. Now, as that same industry begins to explore next-generation materials like WSe2 and MoS2, there’s an opportunity to align flexible photovoltaics with future electronic systems — not just in the lab, but across shared infrastructure, tools, and manufacturing ecosystems.

“We’re not just publishing papers,” he adds. “We’re working toward materials and processes that can power real-world systems — sustainably, efficiently, and at scale.”

Want to dive deeper into the science?

Explore recent publications by Sarallah Hamtaei and collaborators:

• The challenge of making CIGS on stainless steel substrates  (NPJ Flexible Electronics, 2023)
  Talking about the issues of using stainless steel for CIGS solar cells.
• WSe2 thin films on 6-inch wafers via atmospheric pressure CVD (ACS Nano, 2024)
  Introduces a scalable, clean synthesis route for WSe₂ thin films — key to future high-performance flexible photovoltaics.
• ALD grown MoS2 thin films with outstanding radiation tolerance (IEEE PVSC, 2025)
• Flexible CIGS with non-toxic materials, and optimal bandgap for tandem solar cells (Nature Communications Materials, 2024)
  Explores the device-level performance and flexibility of CIGS solar cells made on ultra thin glass.