Exciton Localization in Dion–Jacobson and Mixed-Spacer 2D Lead Bromide Perovskites Constructed with 1,4-Butanediammonium Cations

High Resolution Image Download MS PowerPoint Slide 2D organic–inorganic perovskites with two or even three kinds of organic cations are increasingly being synthesized and studied for optoelectronic applications, but complementary measurements of the temperature dependence of near-bandgap emission and absorption are missing along with these studies. Furthermore, there are very few analogues with different interlayer distances. In this work, we report the synthesis of two layered lead bromides, Ruddlesden–Popper (BDA)(FA)Pb 2 Br 7 (BDA 2+ = 1,4-butanediammonium, FA + = formamidinium) with the same interlayer distances and (BDATz 2 )(Tz 4 )Pb 4 Br 16 (Tz + = 1,2,4-triazolium), the first example of a 2D perovskite with different interlayer distances, in which one of the layers is built up from two different cations (Tz + and BDA 2+ ). Detailed studies of their PL and transmission spectra over a very broad temperature range revealed that these two perovskites exhibit very similar features, i.e., a temperature-dependent bandgap characteristic of 2D perovskites and an unusually significantly broadened near-bandgap emission that shifts very weakly with temperature. This emission was attributed to a localized exciton (LE) on potential fluctuations originating from crystal imperfections. This work highlights the importance of structural defects and long-range disorder in modulating optical properties of layered perovskites constructed using two or more organic cations.