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)₇Pb₆Br₂₆ (PDA = 1, 3-propanediammonium) and a 1D nanobelt-shaped (EDA)₂PbBr₆ (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)₇Pb₆Br₂₆, and (EDA)₂PbBr₆ 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.