(Invited) Triplet Energy Transfer at Interfaces between Molecules and Perovskite or Metal Chalcogenide Nanostructures

Abstract

The movement of energy and charge at nanoscale interfaces between organics and inorganics could enable novel schemes for photoconversion. We have been exploring ligand exchange and functionalization for nanoscale semiconductors with tunable properties. Lead chalcogenide quantum dots (QDs) have near-infrared band gaps that are ideal for solar harvesting and can be tuned to resonance with molecular ligands that harbor triplet excitons. Photoexcitation of either ligand or QD sets in motion energy transfer processes that have kinetics defined by nanocrystal band gap, triplet energy, and the arrangement and distance of molecules on the QD surface. Energy or charge transfer on a ps timescale can inhibit production of triplets by singlet fission, but strategies for enhancing the singlet fission rate or isolating the molecules from direct contact with the QD surface are being studied to circumvent this problem. In CsPbBr3 nanocrystals, ligand exchange with pentacene derivatives produces complementary absorption spectra for organic and inorganic components. Excitation of the strongly absorbing nanocrystal leads to energy transfer to the pentacene singlet, which undergoes fast singlet fission. The yield of triplets compared to absorbed photons is greater 100%, and the triplet lifetime is into the microsecond time range. Further dependence on the preparation conditions of the system (e.g., solution vs. film) is being explored. Other investigations have involved incorporating specialized molecules for attachment to transition metal dichalcogenides (TMDCs). The focus is on producing a uniform layer of bound molecules on the planar surfaces and understanding the interplay between interfacial charge-transfer and other photophysical properties like singlet fission.