Stabilizing the Surface of Metal Halide Perovskite Nanocrystals for Grafting Functional Charge Carrier Acceptors and Polymer Matrixes

Protecting the vulnerable surface of perovskite nanocrystals (PNCs) while creating facile charge carrier migration pathways across the ligand interface is a dilemma that is confronted by researchers in many scenarios of applications. Previous work from our group demonstrated that the overabundant synthetic ligands required for passivating the PNC’s dynamic surface in the colloidal phase were a major obstacle to establishing strong electronic coupling between the perovskite core and external molecular acceptors. We therefore devised a strategy where we first reconstruct the surface ligand layer of PNCs using small molecule zwitterion ligands (ZLs), and we then investigate various surface functionalization methods. By carefully selecting the binding affinity of the initial reconstructing ZLs, we not only successfully stabilize the PNC surface in solution with a low ligand loading, but we also facilitate quantitative grafting of various functional structures via bidentate coordination anchoring motifs. Functional species that can be tightly anchored to the PNC surface using this strategy include molecular charge carrier, organic semiconductors, and precursors that can carry out photopolymerization reactions. We illustrate the surface functionalization process step by step using NMR and steady-state optical spectroscopy. The rapid migration of photogenerated electrons and holes between the PNC and the grafted functional molecules is observed with time-resolved photoluminescence and transient absorption spectroscopy, confirming that the functionalization strategy can establish strong electronic coupling. The molecular charge carrier acceptors grafted on the PNC surface do not create surface trap states but can serve as routes for extracting the excitonic energy. By inducing the photopolymerization of precursors anchored in the PNC ligand shell, we generate a polymer matrix that tightly wraps the PNC core to enhance their stability. We monitor the dynamics of charge carriers shuffling through the polymer layer using time-resolved optical spectroscopy and adjust the polymerization condition to achieve balanced protection and charge transport mobility.