Origin of Broad Emission Induced by Rigid Aromatic Ditopic Cations in Low-Dimensional Metal Halide Perovskites

The development of broadband emitters based on metal halide perovskites (MHPs) requires the elucidation of structure-emission property correlations. Herein, we report a combined experimental and theoretical study on a series of novel low-dimensional lead-chloride perovskites including ditopic aromatic cations. Synthesized lead-chloride perovskites and their bromide analogues show both narrow and broad photoluminescence emission properties as a function of the cation and halide nature. Structural analysis shows a correlation between the rigidity of the ditopic cations with the lead-halide octahedral distortions. Density functional theory calculations reveal, in turn, the pivotal role of octahedral distortions in the formation of self-trapped excitons which are responsible for the insurgence of broad emission and large Stokes shifts together with a contribution of halide vacancies. For the considered MHPs series the use of conventional octahedral distortion parameters allows to nicely describe the trend of emission properties thus providing a solid guide for further materials design.