Facilitating Energy and Charge Transfer from CsPbBr Perovskite Nanocrystals via Ligand Shell Reconstruction.

Efficiently extracting photon energy from colloidal lead halide perovskite nanocrystals (PNCs) as excitons and charge carriers is a crucial step in many applications of these materials. We herein report a functionalization strategy based on reconstructing the surface chemical environment of CsPbBr PNCs to strengthen the binding of acceptor motifs and, thereby, enhance energy and charge carrier transfer efficiency. A zwitterion ligand, 2-ammonium benzenesulfonate, was employed to protect the integrity of the PNC surface during a purification step for removing excess original synthetic ligands. Heterocyclic-carboxylate structures with strong chelating binding effects were utilized as the anchoring motifs to couple the acceptors to the PNC surface. Compared to directly applying the acceptors to as-synthesized PNCs, the new method achieved at least a 6-fold increase in transportation efficiency for both an oligothiophene triplet energy acceptor and a quinoline-derivative electron acceptor. NMR spectroscopy systematically analyzed the binding conditions of different surface ligands in each step of functionalization. The improved functionalization was attributed to the diminishment of competitive adsorption after the purification step. We identified the N-heterocyclic-carboxylate structure as the most effective anchoring group. Transient absorption spectroscopy was employed to monitor the triplet energy transfer and charge carrier migration processes in the PNC-acceptor complexes and evaluate their rate constants. Spectral and dynamic features for distinguishing the electron transfer process from triplet energy transfer were summarized. Our surface reconstruction strategy will benefit the development of PNC-based optoelectronics and promote the application of perovskite materials as photosensitizers in different photophysical and photochemical processes.