Structure–Emission Property Relationship of Bilayer 2D Hybrid Perovskites

Two-dimensional hybrid perovskites (2D-PVKs) have shown great promise for optoelectronic applications. However, the structure-emission property relationship of 2D-PVKs, particularly those with multiple octahedral layers in the metal-halide lattice (<i>n</i> > 1), is not fully understood. Here we combine experimental and theoretical studies to investigate a series of bilayer (<i>n</i> = 2) 2D-PVK crystals in both Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases. Our results reveal that DJ-phase crystals exhibit a higher degree of octahedral lattice distortion compared with RP-phase crystals, with this distortion scaling inversely with interlayer spacing. Such octahedral distortion leads to (1) lower formation energies for iodine vacancies that act as nonradiative recombination centers, thereby reducing light emission yields, and (2) local inversion asymmetry that impacts electronic band structure and light emission properties. Among all the studied crystals, the DJ-phase crystal based on 4-(aminomethyl)piperidinium cations demonstrates the largest intra- and interoctahedral distortions, leading to inversion asymmetry that causes significant Rashba band splitting and circular-polarization dependent photoluminescence at room temperature. Our results provide insights into the development of 2D-PVKs for future optoelectronic/spintronic applications.