Flexible gadgets like smartwatches and foldable phones can break from hidden cracks. Learn how tiny cracks can make these devices stop working.
Demand for flexible electronics, from health monitors and smartwatches to foldable phones and portable solar panels, is growing rapidly. But new research from Brown University engineers shows that these devices may be more fragile than previously thought. Cracks that form in ceramic electrode layers can spread into the polymer substrate beneath, undermining performance and longevity.
Flexible electronics rely on layered designs. The top layer, usually made of transparent ceramic oxides, conducts electricity for displays, sensors, and solar cells. Ceramics are brittle, so the underlying polymer substrate provides toughness and flexibility. Until now, polymers were assumed to resist cracking under repeated bending.
Researchers studied how fatigue degrades flexible solar cells. They built small devices with different ceramic electrodes and polymer substrates, bending them repeatedly while using electron microscopy to track crack formation. In cracked areas, focused ion beams removed the ceramic to reveal damage in the polymer below.
The study found that cracks in ceramic layers often drive deeper cracks into the polymer substrate, a failure mechanism seen across multiple material combinations. Once these substrate cracks form, repeated bending widens them, misaligns layers, or traps debris, increasing electrical resistance and reducing device performance.
Further analysis showed that mismatched elastic properties between ceramic and polymer layers drive deep cracking. To counter this, the team tested a third layer between the ceramic and polymer to reduce elastic mismatch. By selecting polymers of specific thickness, they were able to prevent cracking across various electrode and substrate combinations. Experiments confirmed the approach works.
The findings highlight a previously unrecognized challenge in flexible electronics and offer a roadmap to more durable devices. Engineers can now design flexible gadgets that better withstand repeated folding, helping make next generation wearables, foldable phones, and portable solar panels more reliable.
