Strong Exciton–Photon Coupling in Microfluidic Confined Grown 2D Dion–Jacobson Perovskite

Dion–Jacobson (DJ) perovskites represent a promising class of 2D semiconductors characterized by exceptional features and enhanced stability compared to their classic Ruddlesden–Popper (RP) counterparts. The inclusion of dications offers the potential for increased structural rigidity, leading to the formation of more distorted lead halide octahedra. However, their application as single crystals in nanophotonic structures is hindered by the inability to precisely tune their thickness. In this study, we introduce a straightforward method for obtaining DJ perovskites with the desired thickness and shape through template‐confined growth. The high quality of the synthesized perovskites is leveraged to achieve exciton–photon strong coupling at room temperature, without the need for an external optical cavity, by simply using the high crystal quality, leading to perfect interfaces. The stability of DJ perovskites, together with their pronounced in‐plane octahedral distortion, provides a promising platform for exploring this emerging class of materials in the context of topological phenomena.