Optoelectronic Properties of Two-Dimensional Bromide Perovskites: Influences of Spacer Cations

Two-dimensional (2D) halide perovskites have displayed unique emission properties, making them potential candidates for next-generation light-emitting devices. Here, we combine nonadiabatic molecular dynamics and time-domain density functional theory to investigate the fundamental mechanisms of carrier recombination processes. Considering monolayer bromide perovskites with dissimilar organic spacer molecules, n-butylammonium (BA) and phenylethylammonium (PEA) cations, we find a strong correlation between temperature-induced structural fluctuations and nonradiative carrier recombination rates in these materials. The more flexible geometry of (BA)₂PbBr₄ compared to that of (PEA)₂PbBr₄, results in faster electron-hole recombination and shorter carrier lifetime, diminishing the photoluminescence quantum yield for softer 2D perovskites. Reduced structural fluctuations in relatively rigid (PEA)₂PbBr₄ not only indicate of a longer carrier lifetime but also suggest a narrower emission line width, implying a higher purity of the emitted light. Our ab initio modeling of excited state properties in 2D perovskites conveys material designing strategies to fine-tune perovskite emissions for solid-state lighting applications.