Illustrating the Key Role of Hydrogen Bonds in Fabricating Pure-Phase Two-Dimensional Perovskites

Two-dimensional (2D) layered perovskites consisting of multiple quantum wells are emerging as functional materials to achieve high-performance and stable optoelectronic devices. Pure-phase 2D perovskites provide a platform to investigate their fundamental properties; however, the deposition of pure-phase films remains a scientific challenge. Herein, we reveal the critical role of hydrogen bonds in fabricating pure-phase 2D perovskites. We demonstrate that the phenylalkylammonium molecules exhibit different hydrogen bonding abilities with formamidinium (FA) by varying their alkyl chain lengths. The stronger hydrogen bonding-assisted FA localization at the corner of [PbBr₆]^4- octahedral layer plays a key role in the crystallization of n = 2 pure-phase perovskites. On the basis of these understandings, we demonstrate deep-blue electroluminescence with an emission peak at 442 nm and a narrow line width of 13 nm, showing a peak external quantum efficiency of 0.19%. This finding opens up a new avenue for domain distribution control of 2D perovskites.