Ligand Design Rules for Improving 2-D Organic-Inorganic Hybrid Halide Perovskite Moisture Stability

Organic-inorganic hybrid halide perovskites are promising semiconductor materials due to their long carrier lifetimes, diffusion lengths, and tunable band gap. Two-dimensional (2-D) Ruddlesden-Popper halide perovskites are particularly interesting from an optoelectronics device standpoint due to broad range of organic ligands that can be incorporated into the perovskite lattice and ease of fabrication. However, a major challenge for perovskite optoelectronics is their sensitivity to moisture, leading to chemical instability and device reliability issues. Here, we show that judicious choice in selection of the surface cation for a 2-D perovskite prevents water from penetrating into and dissolving the inorganic layer. We use molecular dynamics simulations to elucidate general design rules for designing water-proofing surface cations, showing that the length/size of the surface ligand alone is not sufficient to suppress water penetration. Our results provide insight into the stability-enhancing mechanism and provide a path for designing perovskites with improved properties.