Circularly Polarized Perovskite Luminescence in Composite Films with High Flexibility and Stability

Abstract Flexible circularly polarized luminescence (CPL) exhibits significant potential for applications in smart wearable devices and high‐end anti‐counterfeiting. However, existing technologies suffer from low dissymmetry factor (g_lum) and poor mechanical reliability. Here, a metal halide perovskite is employed as the emitter to construct efficient and robust flexible CPL films through a facile strategy of bilayer stacking, which comprises a layer of perovskite nanocrystalline embedded polymer film and a layer of photonic crystal film based on polymerized chiral liquid crystals (LCs). The photoluminescence efficiency of perovskite nanocrystals in polyacrylonitrile (PAN) matrix is improved by incorporating an appropriate amount of phenylethylammonium bromide (PEABr) as a passivation agent, and the helical arrangement and optical activity of free‐standing flexible photonic crystal films are found to be highly related to the supporting substrates. Upon stacking, the resulting flexible composite film exhibits extremely high |g_lum| values of up to 1.81, representing the highest value among reported flexible CPL‐active films. Moreover, the composite films demonstrate remarkable mechanical robustness, which shows negligible degradation in terms of g_lum value even after 1000 bending cycles at a bending radius of 2 mm. Based on the flexible CPL‐active films, advanced anti‐counterfeit labels with switchable patterns under circular polarizers are demonstrated.