Tuning Charge-Separated State Lifetimes in Perovskite Nanocrystal-Perylenediimide Hybrids

To surface engineer CsPbBr₃ nanocrystals (NCs), the use of functional perylenediimides (PDIs) featuring carboxylic acids of different spacer lengths afforded hybrid materials such as NC@PDI-Ph (phenyl spacer) and NC@PDI-PhPr (phenylpropyl spacer). Properties that are not seen by the individual components, are investigated by an arsenal of steady-state and time-resolved techniques. These ranged from photoluminescence (PL) to ultrafast transient absorption spectroscopy (TAS) combined with global target analyses. Herein, charge separation from NCs to the electron-accepting PDIs upon photoexcitation of either the NC or PDI unities is evidenced. Remarkable is not only the lifetime of the charge carriers, which is on the time scale of microseconds, that is, 34 and 63 µs for NC@PDI-Ph and NC@PDI-PhPr, respectively, but also the control over their lifetimes through tuning phenyl- versus phenylpropyl-spacer length. These findings are of relevance to solar energy conversion, in general, and perovskite-based devices, in particular.