Achieving Long-Term Stability of Ultraflexible OPVs under 1-Sun in Ambient Air Using a UV-Filtering Polyimide Substrate

Ultraflexible organic photovoltaics (OPVs) are promising candidates for next-generation wearable and portable electronics due to their lightweight, flexibility, and conformal properties. However, their long-term operational stability remains a critical challenge, as they are susceptible to degradation from both photo- and mechanical stress. The degradation pathways are further worsened by UV radiation, which degrades the active materials, as well as the device's interfacial and encapsulation layers. We addressed this by fabricating a 3.6 μm-thick polyimide (PI) film that functions as both a flexible substrate and a UV filter with a cutoff wavelength about 380 nm. When encapsulated with parylene, the ultraflexible devices demonstrated exceptional mechanical durability, enduring 4000 cyclic bends at a 0.5 mm radius without performance loss. Under 1-Sun ambient irradiation, the PI film's UV-filtering effect proved to be crucial. It not only prevented internal oxygen generation from the zinc oxide layer but also protected the parylene encapsulation from UV-induced degradation. This dual protection resulted in a T80 lifetime of 160 h for bent devices and approximately 220 h for unbent devices, with performance degradation primarily limited by the top parylene layer.