Mediating Energy and Charge Transfer Dynamics of Lead Halide Perovskite Nanocrystals via Surface Chemical Approaches

Engineering notes

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Chinese explanation / 中文解读

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Original abstract

Energy and charge transfer are the fundamental mechanisms by which semiconductor nanocrystals interact with their external environment and underpin all light-conversion related applications. Lead halide perovskite nanocrystals (PNCs) are a relatively new class of semiconductor nanocrystals that possess a unique and dynamic surface chemical environment. Investigations into the influence of these surface chemical conditions on the electronic coupling between surface-bound molecular acceptors and the perovskite nanocrystals, and how the surface chemistry can be manipulated, in turn controlling the charge and energy transfer mechanisms, is the focus of this dissertation. Through ligand-shell engineering using commercially available, inexpensive small molecules, the surface chemical environment of the perovskite nanocrystals has been tuned for functionalization with various surface-bound molecular acceptors to carry out charge-carrier and triplet-energy transfer. Leveraging the weakly bound intrinsic ligands to introduce protective ligands with appropriate binding affinity facilitated a virtually complete purification of the PNCs’ insulating ligand-shell, strengthening the anchoring of acceptors and their electronic coupling with the donor PNCs. Quantitative addition and tunable coupling strength were achieved for mediating the kinetics of charge and energy transfer. These investigations have resulted in enhanced energy and charge transfer rates, endowed the ability to manipulate charge transfer and recombination rates, and facilitated a novel excited-state equilibrium system, with the capability to increase the PNCs’ exciton lifetime by an order of magnitude. Characterization of the PNC surface’s chemical environment was performed using nuclear magnetic resonance (H1-NMR 1D and 2D), FT-IR, and x-ray photoelectron spectroscopy (XPS). Steady state UV-vis and photoluminescence (PL) were paired with ultrafast time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopies to unravel the mechanisms involved in the evolution of the excited state of the PNC donor acceptor systems.

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