Spectral Heterogeneity of Hybrid Lead Halide Perovskites Demystified by Spatially Resolved Emission

Solution-processed films of methylammonium lead bromide (MAPbBr3) perovskites have remarkable photoluminescence (PL), with utility in light-emitting devices (LEDs) and photodiodes; however, the PL emission is often complex, heterogeneous, anomalous, or poorly understood. We provide a deeper understanding by studying PL spectra of single MAPbBr3 crystallites with intracrystallite spatial resolution. We uncover an emission emanating from the crystallite boundaries that is spectrally distinct from the band-to-band recombination-based emission from the crystallite interiors. Both forms of emission contribute to spatially averaged PL measured on heterogeneous samples. We also map the PL emission spectrum in a distant-dependent manner across a single crystallite. The systematic distance dependence observed reveals that a portion of the PL emission emanating from within a crystallite is waveguided and outcoupled from the boundaries of the crystallite in a form that is spectrally modulated by self-absorption. Spatial heterogeneities, self-absorption, and filtered-emission of PL are all processes that must be considered in the future design of perovskite-based LEDs.