Understanding and Controlling the Photoluminescence Line Shapes of 2D Perovskites with Chiral Methylbenzylammonium-Based Cations

Abstract

Chiral two-dimensional (2D) perovskites are a promising material class for the next generation of spintronic and chiroptical devices. Despite their promise, many aspects related to film formation and crystallization remain elusive. When chiral ammonium-based organic cations such as methylbenzylammonium (MBA) are employed in the preparation of chiral 2D perovskites, their interaction with the halide species in the inorganic perovskite network often introduces substantial steric hindrance, leading to the formation of one-dimensional (1D) phase impurities within the 2D matrix. Here, we demonstrate that this 1D phase manifests itself in the photoluminescence (PL) spectra of the 2D perovskite film as an additional weakly emissive, thermally activated state with a self-trapped excitonic character, leading to an asymmetric PL response. We demonstrate that the strategic introduction of a methoxy (OMe) group on the para position of the MBA cations can mitigate the formation of the 1D phase. As a result, the emission band becomes narrower and more symmetric and the 2D perovskite film has a higher PL quantum yield at room temperature. Our findings elucidate the origins of asymmetry and broadband emission of MBA-based chiral 2D perovskites and highlight the indispensable role of molecular design in chiral organic cations in controlling phase purity and attaining the desired optical properties.