A research team in Italy has developed a novel glass-free, flexible crystalline silicon (c-Si) module architecture based on polyethylene terephthalate (PET) and roll-to-roll lamination.
The researchers analyzed the effectiveness of the roll-to-roll process, cell performance before and after lamination, and the impact of cracked cells on series-connected mini-modules under different operating conditions.
“The main architectural novelty lies in combining commercially mature, 150-μm interdigitated-back-contact crystalline-silicon cells with a fully glass-free PET/EVA/c-Si/EVA/PET stack manufactured through a single-pass, atmospheric roll-to-roll hot-lamination process,” corresponding author Paola Jakuza told pv magazine. “While previous studies have separately demonstrated flexible ultrathin cells or PET-based modules, this architecture integrates flexibility, established c-Si technology and scalable, low-CAPEX processing in one module concept.”
Jakuza said the outer PET layer, typically used as a backsheet in module architectures, provides mechanical protection for the fragile silicon cells in the glass-free configuration.
“It mitigates stresses associated with impact, vibration and thermo-mechanical loading induced by temperature variations,” she said. “Replacing glass with PET-based layers also leads to a significant reduction in the overall module weight compared to the glass/glass counterpart.”
The researchers fabricated the modules using commercial SunPower Maxeon Gen III IBC cells rather than producing the cells themselves. They tested bare cells as a reference, as well as single-cell 1 × 1 modules and 2 × 2 modules comprising four series-connected cells.
The researchers laminated the module stack with a commercial hot-roll laminator to emulate a roll-to-roll process. The baseline process used a soldering temperature of 390 C, a roller temperature of 130 C, a roller speed of 9 mm/s and a roller spacing of 2 mm.
They characterized the devices using current-voltage measurements, external quantum efficiency (EQE), reflectance, electroluminescence and infrared thermography. They compared cells before and after lamination, varied key roll-to-roll parameters, and bent 1 × 1 and 2 × 2 modules to radii of about 95 mm and 155 mm, respectively.
The scientists also studied modules containing cracked cells to assess mismatch and hot-spot formation. Finally, they mounted a 2 × 2 module on a curved support with a 150 mm radius and tested it outdoors under continuous short-circuit conditions for 672 hours to track electrical degradation and crack propagation.
“The combined use of current-voltage measurements, EQE, integrating-sphere reflectance and electroluminescence demonstrates that the approximately 4.4% relative post-lamination efficiency loss is predominantly optical – caused by front-surface reflection – rather than the result of electrically active cracks or process-induced cell damage,” Jakuza said.
During mechanical testing, a single-cell module showed no crack formation when bent to a radius of 95.4 mm, corresponding to 0.2% mechanical strain. Its efficiency declined by only about 3.4%, primarily due to non-uniform illumination. The 2 × 2 module, meanwhile, retained 93% of its flat-state power output at a bending radius of 155 mm.
After 672 hours at a fixed bending radius of 150 mm, the 2 × 2 module retained 96.12% of its initial efficiency.
“These measurements were then translated into engineering criteria – including a recommended bending radius above 200 mm, appropriate bonding constraints and thermal-management provisions – linking module design directly to practical building-integrated PV (BIPV) integration and thermomechanical reliability considerations,” Jakuza said.
She said the team plans to reduce reflection losses at the air/PET interface by introducing anti-reflective coatings. The researchers also intend to replace conventional wire soldering with solder paste that can be co-cured and reflowed during the roll-to-roll lamination step.
“The technology was first patented in 2020 by the Institute of Materials for Electronics and Magnetism of the Italian National Research Council (CNR-IMEM) in Parma,” said co-author Stefano Rampino. “It was subsequently developed and implemented over time by CNR-IMEM, with further validation provided by characterization tests carried out at the Department of Engineering of the University of Padua.”
Future work will include longer-term reliability testing, including thermal cycling, repeated bending and outdoor durability tests on alternative curved substrate geometries.
The findings are available in “Roll-to-roll flexible back-contacted c-Si PV modules: performance analysis and impact of mechanical and thermal stress,” published in Solar Energy. Researchers from Italy’s University of Padova and the Institute of Materials for Electronics and Magnetism of the Italian National Research Council (IMEM-CNR) contributed to the research.
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