Simultaneous enhancement of surface hardness and impact strength in flexible and transparent cover windows for organic photovoltaic films

Abstract

The fabrication of flexible and transparent cover windows, which simultaneously have a high surface hardness and impact strength, has been a biggest challenge for their photovoltaic applications. Conventional tempered glass cover windows face severe limitations in realizing multi-curved panoramic shapes due to their rigid nature and the complex manufacturing processes required. Furthermore, their brittle fracture behavior can pose significant safety risks to installers and users in the event of impact. In this study, we develop a highly flexible and transparent polycarbonate (PC) cover window that can be designed with a curved panoramic form and possesses a high surface hardness while maintaining a high impact strength. Notably, when conventional hard coatings are directly applied to bare PC, residual solvents or mechanical mismatch often lead to embrittlement and significant degradation in impact strength. To address this issue, we introduce a siloxane-epoxy hybrid primer layer that effectively mitigates solvent-induced stress cracking and provides excellent interfacial compatibility with the hard coating. The resulting hard-coated PC with the primer exhibits outstanding cover window features, including a high surface hardness, impact strength, optical transmittance, flexibility, and UV stability, which lead to mechanically robust photovoltaic modules that maintain their performance after rigorous abrasion and impact testing.