Defect‐Induced Circularly Polarized Luminescence of Zero‐Dimensional Cs ₄ PbBr ₆ Perovskite Nanocrystals With Ligand‐Ratio Dependent CPL Inversion

ABSTRACT

A defect‐induced strategy is employed to synthesize chiral zero‐dimensional Cs ₄ PbBr ₆ perovskite nanocrystals (NCs) with blue photoluminescence via a phase transformation process. Both the circular dichroism (CD) and circularly polarized luminescence (CPL) spectra of them exhibit characteristic mirror‐symmetric signals, confirming the presence of ground‐state chirality and excited‐state chirality. The transmission electron microscopy (TEM) images and electron paramagnetic resonance spectra (EPR) indicate that the strong blue photoluminescence and CPL response originate from the generation of bromine defects. Particularly, the change in the ratio of ligands not only leads to CD inversion, but also can give rise to CPL inversion. The Ultrafast spectroscopy transient absorption (TA) spectra further show that the CPL response of chiral Cs ₄ PbBr ₆ NCs originates from the spin‐polarization process. The reversal of the CPL signal can be attributed to the changes of energy band structure due to conformational changes with respect to S/R ‐MBA (MBA = α‐Methylbenzylamine) ligands in chiral perovskite NCs. It indicates that the conformational change of chiral ligands can modulate the energy band structure of chiral Cs ₄ PbBr ₆ perovskite NCs with keeping the crystallographic structure constant. Furthermore, the universality of the defect induction strategy can be confirmed by using EBA (EBA = ethylbenzylamine), CHEA (CHEA = cyclohexylethylamine), and NEA (NEA = 1‐(1‐Naphthyl) ethylamine) as chiral precursors.