Enhanced Performance and Stability of Paper‐Based Cs 3 Cu 2 I 5 Photodetectors via PVK In Situ Encapsulation

ABSTRACT The quest for resilient photodetectors in flexible electronics is met with the challenge of perovskite instability under mechanical stress and environmental conditions. This study introduces a Cs 3 Cu 2 I 5 /poly(N‐vinylcarbazole) (PVK) photodetector on paper, where PVK not only encapsulates Cs 3 Cu 2 I 5 to shield it from environmental degradation but also synergistically enhances photoconductive properties. The device exhibits a responsivity (R) of 1.35 A/W, remains stable operation after 5000 bending cycles, and retains 75% of its initial performance following 215 days of exposure.