Interplay of Charge and Energy Transfer in Layered Quantum Dot Assemblies

Charge and energy transfer play crucial roles in tuning the optical properties of quantum dot heterostructures. This study investigates the interplay of Förster resonance energy transfer (FRET) and charge transfer in CuInS₂/CdS|CuFeS₂ and CuInS₂/CdS|CdS|CuFeS₂ layered nanocrystal assemblies. X-ray photoelectron spectroscopy (XPS) confirms charge transfer across the heterojunction, with shifts in binding energy indicating Fermi level equilibration, while photoluminescence measurements reveal strong exciton quenching in CuInS₂/CdS|CuFeS₂. The CuInS₂/CdS film shows a lifetime of 335 ns, while introducing CuFeS₂ reduces the lifetime to 26 ns, indicating strong quenching via charge transfer and FRET. The addition of a CdS spacer extends the lifetime to 209 ns, demonstrating partial suppression of these processes. While charge transfer depletes electrons in CuInS₂/CdS, forming charged excitons with shorter lifetimes, the CdS spacer weakens direct electronic coupling and dipole-dipole interactions, increasing the emission lifetimes. These results show the way interfacial engineering in quantum dot solids controls charge and energy transfer and gives insights into optimizing quantum-dot-based devices.