Halide-Driven Halogen-Hydrogen Bonding versus Chelation in Perovskite Nanocrystals: A Concept of Charge Transfer Bridging

The choice of surface functionalized ligands to encapsulate semiconductor nanocrystals (NCs) is important for tailoring their optoelectronic properties. We use a small bidentate 8-hydroxyquinoline (HQ) molecule to surface functionalize CsPbX3 perovskite NCs (X = Cl, Br, I), along with traditional long-chain monodentate ligands. Our experimental results using optical and ultrafast spectroscopy depict a halogen-hydrogen bonding formation in the HQ functionalized CsPbCl3 and CsPbBr3 NCs, which act as a charge transfer (CT) bridging for the interfacial hole transfer from the NCs to the HQ molecule as fast as 540 fs. In contrast, weak chelation is observed for HQ-coupled CsPbI3 NCs without an active CT process. We explain two distinct surface coupling mechanisms via the polarizability of halides and larger PbI64- octahedral cage size. Control of two contrasting halide-dependent surface coupling phenomena of a small molecule that further regulate the CT process may have significant implications in their development in optoelectronics.

Automated summary

The choice of surface functionalized ligands is crucial for tailoring the optoelectronic properties of semiconductor nanocrystals (NCs). We used a bidentate 8-hydroxyquinoline (HQ) molecule to surface functionalize CsPbX3 perovskite NCs (X = Cl, Br, I), along with traditional long-chain monodentate ligands. Our experimental results revealed a halogen-hydrogen bonding formation in the HQ functionalized CsPbCl3 and CsPbBr3 NCs, which facilitated fast charge transfer from the NCs to the HQ molecule. In contrast, weak chelation was observed in HQ-coupled CsPbI3 NCs without an active charge transfer process.