Grain‐Specific Transitions Determine the Band Edge Luminescence in Dion–Jacobson Type 2D Perovskites

Abstract The photophysics of 2D perovskites incorporating 1,4‐phenylenedimethanammonium (PDMA) as spacer cations is studied. PDMAPbI₄ and PDMASnI₄ exhibit absorption and luminescence spectra dominated by excitonic transitions and an emission due to two different states. Low‐temperature studies reveal a time‐dependent red shift of 12 meV that is correlated with grain‐specific luminescence spectra observed in optical micrographs. For the Pb‐variant, grains of red‐shifted and lower intensity band edge emission simultaneously exhibit a more pronounced luminescence from a broad defect‐related band around 2 eV. This suggests the grain‐specific emission to be related to local defects. These observations have important consequences for the understanding of luminescence of 2D perovskites, for which peak splitting of the band edge emission is a common, yet not completely resolved observation.