Introducing Intermolecular Cation‐π Interactions for Water‐Stable Low Dimensional Hybrid Lead Halide Perovskites

Abstract

Optoelectronically active hybrid lead halide perovskites dissociate in water. To prevent this dissociation, here, we introduce long-range intermolecular cation-π interactions between A-site cations of hybrid perovskites. An aromatic diamine like 4,4′-trimethylenedipyridine, if protonated, can show a long-range cation-π stacking, and therefore, serves as our A-site cation. Consequently, 4,4′-trimethylenedipyridinium lead bromide [(4,4′-TMDP)Pb₂Br₆], a one-dimensional hybrid perovskite, remains completely stable after continuous water treatment for six months. Mechanistic insights about the cation-π interactions are obtained by single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. The concept of long-range cation-π interaction is further extended to another A-site cation 4,4′-ethylenedipyridinium ion (4,4′-EDP), forming water-stable (4,4′-EDP)Pb₂Br₆ perovskite. These water-stable perovskites are then used to fabricate white light-emitting diode and for light up-conversion through tunable third-harmonic generation. Note that the achieved water stability is the intrinsic stability of perovskite composition, unlike the prior approach of encapsulating the unstable perovskite material (or device) by water-resistant materials. The introduced cation-π interactions can be a breakthrough strategy in designing many more compositions of water-stable low-dimensional hybrid perovskites.