Fig. 1. Approaching theoretical limits with superstructural chirality.
In 2017, Moon et al. first investigated the chiroptical properties of 2D chiral perovskite film, reporting CD of 155 mdeg and gCD of 0.00514. In 2018, Sargent et al. achieved CD of 200 mdeg and gCD of 0.006 in a 2D bromide chiral perovskite film. In 2019, Tang et al. reported circularly polarized photodetectors based on a 1D chiral perovskite film with CD of 200 mdeg and gCD of 0.0219. In 2020, Miyasaka et al. reported an encouraging CD of 3200 mdeg and gCD of 0.04 after morphology optimization of the 1D chiral perovskite film25. Switching from structural to superstructural chirality, this work reports high CD of 6350 mdeg and large gCD of 0.49 in a perovskite chiral metasurface obtained by nanostructure engineering. Numerical simulations predict CD of 18900 mdeg and gCD of 1.1 in large area samples, coming closer to the theoretical limits of both parameters. The diamonds and 4-point stars indicate representative studies where metasurface with strong chirality were obtained using conventional optical materials like Au40 and TiO237. The theoretical limits for CD ( ± 45000 mdeg) and gCD (±2) are obtained using the formulas defined in the introduction and correspond to the case of one circular polarization (e.g. LCP) being fully absorbed and the other (e.g. RCP) fully transmitted.