Role of A‐Site Host–Guest Binding Affinity in Governing Ultrafast Hole Dynamics of Perovskite Nanocrystals

ABSTRACT

Charge transport in nanocrystal (NC) systems is strongly influenced by the coupling between the charge acceptors and the surfaces of NCs. Conventional hydrogen bonding often lacks the strength and stability needed for well‐defined composites. We propose that hydrogen bond surrogate motifs offer a more reliable route with enhanced structural precision and improved charge transport properties. Using three isomeric dihydroxybenzenes, e.g., catechol (CAT), resorcinol (RES), and hydroquinone (HQ), as charge acceptors for FAPbBr ₃ (FAPB) NCs, we investigate interfacial hole transfer (HT) dynamics. Ultrafast spectroscopy reveals highly efficient and rapid HT for CAT, significantly reduced HT for HQ, and no observable HT for RES, despite thermodynamic feasibility in all cases. ¹ H NMR and density functional theory calculations indicate that CAT forms two hydrogen bonds with FA ⁺ via adjacent –OH groups, whereas RES and HQ form only one, leading to their weaker coupling. The relative binding affinities of these isomers toward FAPB are further rationalized through their ionization potentials and dipole moments. The interplay between stronger binding energy and thermodynamic driving force in FAPB/CAT results in ultrafast HT with a rate as high as 4.8 × 10 ¹⁰ s ⁻¹ . Similar studies with CsPbBr ₃ NCs show slower HT with CAT, which interacts with Cs ⁺ via chelation. Collectively, these findings establish that the nature of the interaction between host A‐site cations and guest molecular acceptors governs the balance of picosecond HT dynamics.