Hot carrier transfer from CsPbBr3 nanocrystals to Au25 clusters: the pivotal role of ligand-controlled diffusion.

Efficient hot carrier extraction from a lead halide perovskite is the key to overcoming its Shockley-Queisser limit. The interaction of the perovskite surface with an acceptor plays a vital role in controlling the charge transfer process. Here, we have investigated the charge transfer from CsPbBr₃ nanocrystals to Au₂₅ clusters. Ultrafast pump-probe spectroscopy confirms that the Au₂₅ cluster can efficiently extract hot carriers from the CsPbBr₃ nanocrystal. The effect of the ligand environment on the hot carrier transfer is studied by taking oleic acid/oleylamine (pristine) and trioctylphosphine-capped CsPbBr₃ nanocrystals of similar sizes. The experimental data show that the ligand-controlled diffusion mechanism governs the charge transfer process rather than anchoring. The hot carrier transfer process is found to be dependent on the effective interaction distance between the nanocrystal surface and Au₂₅ controlled by the ligand environment. The hot carrier transfer rate to the Au₂₅ cluster is estimated to be almost double for trioctylphosphine-capped CsPbBr₃ nanocrystals (9.53 × 10¹¹ s^-1) compared to that of pristine nanocrystals (5.47 × 10¹¹ s^-1). Thus, optimizing the ligand environment of the perovskite nanocrystals is essential for Au₂₅ to harvest the hot carriers.