Elucidating interfacial charge extraction from CdTe@ZnS quantum dots by pyridinium ionic liquids

Interfacial defects, energy-level mismatch, and material instability at the electron transport layer (ETL)/quantum dot (QD) interface have remained major bottlenecks for QD-based solar cells, limiting their efficiency. In this scenario, modifying QDs with ionic liquids (ILs) that can also act as efficient electron extractors is expected to provide a viable solution to these issues. Although ILs have been widely used to improve QD stability, their role as photoinduced electron acceptors from QDs has not yet been established. Herein, we report investigations of the photoinduced charge-transfer dynamics between CdTe@ZnS QDs and a series of pyridinium-based ILs-C₃PyBr, C₆PyBr, and [C₆Py₂]Br₂-chosen for their strong electron-accepting characteristics. Steady-state photoluminescence measurements reveal pronounced quenching of QD emission upon interaction with the ILs, while Stern-Volmer analysis demonstrates contributions from both static and dynamic quenching pathways, with the dicationic IL ([C₆Py₂]Br₂) exhibiting the highest quenching efficiency. Time-resolved photoluminescence measurements further confirm substantial reductions in QD lifetimes, indicating efficient electron transfer from the QDs to the IL acceptors. Furthermore, zeta potential measurements have indicated that the interaction between the QDs and ILs is predominantly electrostatically driven. Ultrafast transient absorption spectroscopy provides direct evidence of accelerated carrier extraction and faster bleach recovery in the QD-IL hybrid systems, validating the proposed photo-induced electron-transfer mechanism. Collectively, these findings establish pyridinium-based ILs as effective electron acceptors capable of modulating exciton dynamics in CdTe@ZnS QDs. The insights gained from this work offer a fundamental understanding of interfacial electron transfer in QD-IL hybrid systems and provide valuable guidance for designing advanced optoelectronic and energy-conversion materials that integrate both QDs and ILs.