Rationally-Designed Organic Ligands for Water-Proofed 2D Perovskites

Two-dimensional (2D) halide perovskites have attracted considerable attention as semiconducting materials due to their broader design space of organic ligands compared to their 3D counterparts while retaining favorable properties such as solution-processable, long carrier diffusion length and lifetime, high carrier mobility, etc. However, perovskites suffer from environmental stability issues, particularly intolerance to moisture, that limit their device applications. Here, the role of organic ligands in improving the water-proofing ability of perovskite is interrogated by a joint computational and experimental study: free energy (FE) calculations for water penetration and the synthesis and characterization of down-selected ligands. The FE curves and the subsequent experimental synthesis on investigated aliphatic and conjugated ligands with systematically varied length, bulkiness, and backbone rigidity revealed two chief components for effective water-proofing: (1) ligands length; (2) small free volume, i.e., a large cross-section, which can be realized by increasing terminal bulkiness or modifying backbone torsion. These findings pave the way for the use of π-conjugated molecules with water-proofing while retaining desirable optoelectronic properties and functions.