Ultrastable Perovskite Encased in a Helical Cage for Tunable Full‐Color Mirror‐Image Circularly Polarized Luminescence

Achieving stable and efficient circularly polarized luminescence (CPL) from achiral perovskite nanocrystals (PNCs) remains a major challenge in the development of advanced chiroptical materials. Herein, the syntheses of a total of nine compounds, including full‐color colloidal polymer‐capped PNC composites are reported based on organic‐inorganic hybrid perovskites and inorganic 2D nanosheets (NSs) using phenacyl halide as a single organic source of halide precursor. While the initial PNCs exhibit low photoluminescence quantum yield (PL QY) and poor stability, a previously unexplored surface absorption/ion exchange strategy employing 2D‐ZrH 2 P 2 O 8 NSs significantly enhances both optical properties and long‐term stability, e.g., the FAPbBr 3 @ZrH 2 P 2 O 8 (FA = formamidinium) composite exhibits a significantly enhanced PL QY of 88.57%, compared to 30.9% for the pristine counterparts, owing to the protective effect of the robust 2D ZrH 2 P 2 O 8 network that enhances stability under ambient conditions. Crucially, embedding these stabilized PNCs into a chiral polymer matrix induces distinct mirror‐image strong CPL signals both in solution and solid‐state. This rare dual‐phase CPL activity arises from the conformational adaptability of the chiral polymer, which imparts chirality to the achiral PNCs via both covalent and non‐covalent interactions. These findings present a versatile strategy for producing robust, CPL‐active stable perovskite materials across the visible spectrum for next‐generation chiroptoelectronic devices.