Strong Coupling of Exciton and High‐Q Mode in All‐Perovskite Metasurfaces

Abstract Recently developed halide perovskite semiconductors are viewed as an excellent platform to realize exciton‐polariton at room temperature due to their large oscillation strength. Here, the optimized strong coupling between the exciton of perovskite and quasi‐bound state in the continuum (QBIC) with high‐quality factor (Q‐factor), supported by all‐perovskite metagrating, including magnetic dipole (MD)‐QBIC and toroidal dipole (TD)‐QBIC is demonstrated. By taking advantage of extreme electric field confinement enabled by a high‐Q mode, it is found that the maximum Rabi splitting can be enhanced up to a record high value of 400 meV, almost twice the Rabi splitting reported in the same perovskite‐based subwavelength metasurface. The simulation results reveal that both the Q‐factor of QBIC mode and the thickness of the perovskite metasurface play dominant roles in the enhanced strong coupling. It is also demonstrated that adding a protection layer of poly(methyl methacrylate) on the top of the perovskite metagrating has a negligible effect on the maximized Rabi‐splitting. These results suggest a new approach for studying exciton‐polaritons and may pave the way toward flexible, large‐scale, and low‐cost integrated polaritonic devices and the realization of polariton lasing at room temperature.