Molecular and Self‐Trapped Excitonic Contributions to the Broadband Luminescence in Diamine‐Based Low‐Dimensional Hybrid Perovskite Systems

Abstract The present solid state lighting (SSL) technology is based on using a combination of phosphors to give the desired white light emitting devices. The property of broadband emission from a single phosphor is not only difficult to achieve but also poses a challenge in device fabrication. Hybrid organic–inorganic perovskites especially in low dimensions (2D/1D) are being widely explored for their optoelectronic properties. Few of these materials exhibit broadband emission upon ultraviolet excitation, providing a scope for synthetic engineering in achieving commercially viable single‐phosphor materials. In this work, three interesting diammonium‐based low‐dimensional hybrid perovskites for broadband photoluminescence (PL) are examined. The doubly protonated ethylenediamine‐configured monoclinic (P2₁/n) 1D ribbon assembly (H₃NCH₂CH₂NH₃)₈(Pb₄Br₁₈) · Br₆ (1) and the orthorhombic (Pbcm) 2D‐twisted octahedral (H₃NCH₂CH₂NH₃)(Pb₂Cl₆) (2) show white luminescence, while the doubly protonated piperazine‐configured orthorhombic (Pnnm) 0D dual‐octahedral (C₄N₂H₁₂)₄(Pb₂Br₁₁) · (Br)(H₂O)₄ (3) exhibits bluish‐white luminescence. Based on the PL of the organic diammonium salt, the time‐resolved PL, Raman signatures, and density functional theory (DFT) calculations, it is shown that the broadband luminescence has dual origin: one around 400 nm from diammonium‐related molecular fluorescence and another around 516 nm from self‐trapped excitons. The structure‐specific relative contributions and interplay between the two define the overall character of the broadband luminescence.