Tuning Interlayer Couplings and Stabilizing 2D Perovskite Lattices through Intercalation Chemistry

Two-dimensional (2D) organic-inorganic hybrid lead halide perovskites are promising semiconductors for optoelectronics, spintronics, and ferroelectrics due to their versatile structural and physical properties enabled by a variety of organic spacer cations. While previous research has focused on new spacer cations for templating 2D perovskite structures and influencing their properties, the intercalation of functional molecules within the organic layers has been less explored. Here, we demonstrate the intercalation of iodine within the organic sublattice as an effective tool to tune interlayer electronic interactions and stabilize 2D perovskite structures that would otherwise not form. We synthesized and determined the single-crystal structures of seven new iodine-intercalated 2D perovskites with varying spacer cations and inorganic compositions. The intercalated iodine bridges neighboring inorganic layers via halogen bonding with the apical iodides, leading to interlayer vibrational and electronic couplings. The iodine intercalation enhances the lattice rigidity, which decreases phonon-phonon scattering and exciton-phonon coupling. Adjusting the inorganic composition further tunes the electronic band structures, because iodine's frontier orbitals contribute differently to the band edge states, leading to varied band alignments and photoluminescence quenching behaviors. Moreover, a decreased anisotropic emission polarization is observed after iodine intercalation due to the decreased in-plane confinement of the excitons. Our results demonstrate iodine intercalation as a powerful tool for tuning the structural and optoelectronic properties of 2D perovskites.