Transforming Colloidal Cs4PbBr6 Nanocrystals by Poly(maleic anhydride-alt-1-octadecene) into Stable CsPbBr3 Perovskite Emitters Through Intermediate Heterostructures

The preparation of strongly emissive CsPbBr₃ perovskite nanocrystals with a robust surface passivation is a challenge in the field of lead halide perovskite nanomaterials. We report an approach to prepare polymer-capped CsPbBr₃ perovskite nanocrystals by reacting oleylammonium/oleate-capped Cs₄PbBr₆ nanocrystals with poly(maleic anhydride-alt-1-octadecene) (PMAO). PMAO contains succinic anhydride units that are reactive towards the oleylamine species present on Cs₄PbBr₆ nanocrystals’ surface and produces polysuccinamic acid, which, in turn, triggers the Cs₄PbBr₆ to CsPbBr₃ conversion. The transformation occurs through the formation of Cs₄PbBr₆-CsPbBr₃ heterostructures as intermediates, which were captured because of the mild reactivity of PMAO and were investigated by high-resolution electron microscopy. The Cs₄PbBr₆-CsPbBr₃ heterostructures demonstrate a dual emission at cryogenic temperature with an indication of the energy transfer from Cs₄PbBr₆ to CsPbBr₃. The fully-transformed CsPbBr₃ NCs have high photoluminescence quantum yield and enhanced colloidal stability, which we attribute to the adhesion of polysuccinamic acid to the NC surface through its multiple functional groups in place of oleate and alkylammonium ligands. The PMAO-induced transformation of Cs₄PbBr₆ NCs opens up a strategy for the chemical modification of metal halide NCs initially passivated with nucleophilic amines.