Thin and Flexible Organic Photovoltaic Devices Engineered to Resist Both Mechanical and Thermal Stress
June 29, 2018 | RIKENEstimated reading time: 2 minutes

A flexible polymer-based solar cell that can be heated up to 120 degrees Celsius without reducing its ability to harvest energy has been developed by a team led by RIKEN researchers. The combination of flexibility and thermal robustness makes it attractive for powering wearable sensors and devices.
Image caption:Photograph of 3-micrometer-thick organic solar cell that was adhered to textile by an instant hot-melt process.
Organic solar cells use conductive, carbon-based polymers instead of rigid silicon to capture sunlight and convert it into electricity. They can thus be attached to irregular backings such as clothing without breaking.
Previously, Kenjiro Fukuda of the RIKEN Center for Emergent Matter Science and his team had encapsulated organic solar cells in other polymers to improve their compatibility with textiles by making them tougher and more water resistant.
However, one problem that still limits the long-term lifetime of flexible solar cells is their poor resistance to temperature changes. Thermal stress can make polymers brittle or cause them to become less conductive through expansion.
Fukuda, with group leader Takao Someya and colleagues from Japan and the United States, overcame this problem and fabricated organic solar cells with enhanced thermal stability by modifying the device’s active layer—a complex, light-absorbing polymer composed of fluorine atoms and sulfur-containing aromatic rings. Adding linear hydrocarbon chains to this molecule triggered the aromatic rings to stack in a ‘face-on’ orientation that boosted the polymer’s crystal strength.
The team replaced the conventional plastic substrates used to support the active layer with transparent polyimides that are mechanically stable over a wide temperature range. To form the polyimide film on a supporting plate, they used a wet-chemistry process, rather than vacuum deposition, since it is more amenable for fabricating large-area films.
But a wet-chemistry process necessitates carefully controlling the substrate’s surface energy: if the substrate is too hydrophobic, the polyimide precursor solution will bead and not form a film, whereas if it is too hydrophilic, the polyimide film will adhere too strongly, making it hard to peel off. The researchers achieved the right surface energy by adjusting the thickness of a hydrophobic layer and treating it with oxygen plasma.
Following a final encapsulation step, they tested the behavior of their solar cell as it was rolled, folded, and crumpled repeatedly at different temperatures. The power conversion efficiencies remained at near-record rates despite the mechanical and thermal stress. This inspired the group to attach the devices to fabrics using ‘hot-melt’ technology developed for the apparel industry.
“The hot-melt process gives almost perfect adhesion of our ultrathin organic solar cells onto textiles, with no degradation in performance,” says Fukuda. “We’re now discussing these results with our collaborators to find a good strategy for commercialization.”
Suggested Items
Smarter Machines Use AOI to Transform PCB Inspections
06/30/2025 | Marcy LaRont, PCB007 MagazineAs automated optical inspection (AOI) evolves from traditional end-of-process inspections to proactive, in-line solutions, the integration of AI and machine learning is revolutionizing defect reduction and enhancing yields, marking a pivotal shift in how quality is managed in manufacturing.
Magnalytix and Foresite to Host Technical Webinar on SIR Testing and Functional Reliability
06/26/2025 | MAGNALYTIXMagnalytix, in collaboration with Foresite Inc., is pleased to announce an upcoming one-hour Webinar Workshop titled “Comparing SIR IPC B-52 to Umpire 41 Functional & SIR Test Method.” This session will be held on July 24, 2025, and is open to professionals in electronics manufacturing, reliability engineering, and process development seeking insights into new testing standards for climatic reliability.
The Death of the Microsection
06/26/2025 | Bob Neves, Reliability Assessment Solutions, Inc.I got my start out of college grinding and polishing PCB microsections. My thumbs are a bit arthritic today because of the experience (microsection grinders know what I mean). Back then, via structures were rather large, and getting to the center in six steps of grinding and polishing was easy compared to what my team has been doing recently at the lab.
Specially Developed for Laser Plastic Welding from LPKF
06/25/2025 | LPKFLPKF introduces TherMoPro, a thermographic analysis system specifically developed for laser plastic welding that transforms thermal data into concrete actionable insights. Through automated capture, evaluation, and interpretation of surface temperature patterns immediately after welding, the system provides unprecedented process transparency that correlates with product joining quality and long-term product stability.
Knocking Down the Bone Pile: Tin Whisker Mitigation in Aerospace Applications, Part 3
06/25/2025 | Nash Bell -- Column: Knocking Down the Bone PileTin whiskers are slender, hair-like metallic growths that can develop on the surface of tin-plated electronic components. Typically measuring a few micrometers in diameter and growing several millimeters in length, they form through an electrochemical process influenced by environmental factors such as temperature variations, mechanical or compressive stress, and the aging of solder alloys.