From Distortion to Disconnection: Linear Alkyl Diammonium Cations Tune Structure and Photoluminescence of Lead Bromide Perovskites

Organic ammonium cations play a vital role in building structures and tuning energy bands of organic-inorganic halide perovskites and the consequent photoelectric characteristics. Here, two 2D lead bromide perovskites: flat-layered (BDA)PbBr4 (BDA = 1, 4-butanediammonium), corrugation-layered (PDA)(7)Pb6Br26 (PDA = 1, 3-propanediammonium) and a 1D nanobelt-shaped (EDA)(2)PbBr6 (EDA = ethylenediammonium) are built to explore their tunable structure, energy bands, and photoluminescence by a series of linear alkyl diammonium cations. Significant "spatial effect" of diammonium cations directly controls the space configurations of these lead bromide perovskites. From 2D (100)-flat to 1D (110)-nanobelt, distortions and disconnections of lead bromide layers are beneficial to the quantum confinement and generation of self-trapping exciton (STE) energy levels of low-dimensional perovskites. Upon ultraviolet excitation, (BDA)PbBr4, (PDA)(7)Pb6Br26, and (EDA)(2)PbBr6 exhibit blue, broadband yellowish white, and "warm" white emissions, respectively. Density functional theory combining STE theory demonstrates their bandgap changes and emission mechanisms. This work provides a basis for tuning the structure of low-dimensional organic-inorganic halide perovskites for better photochromic properties.