Intralayer bidentate diammoniums for stable two-dimensional perovskites

Two-dimensional (2D) metal halide perovskites have attracted considerable attention for optoelectronic applications. Conventional 2D perovskites include Ruddlesden-Popper (R-P), Dion-Jacobson (D-J) and alternating cation phases. Here we introduce a class of 2D perovskite incorporating intralayer bidentate ligands, termed B-D phase perovskites, designed to enhance structural diversity and stability. We synthesized bidentate ligands with a rigid core unit and two ipsilateral ammonium-terminated linker groups, and obtained single crystals incorporating these B-D ligands with intralayer bidentate coordination. Molecular dynamics simulations reveal that the B-D ligand exhibits stronger binding energies to the inorganic layer compared with its R-P and D-J phase counterparts. Polycrystalline thin films of B-D phase showed superior thermal resistance, outperforming R-P and D-J phase analogues by 1,600% and 140% respectively, based on absorption stability assessments. Photovoltaic devices incorporating the B-D ligand exhibited higher power conversion efficiency and extended stability. These findings establish B-D phase 2D perovskites as a promising platform for next-generation optoelectronic applications, advancing ligand engineering for metal halide perovskites and other hybrid materials.