Compositionally Tuning Electron Transfer from Photoexcited Core/Shell Quantum Dots via Cation Exchange

It is critical to find methods to control the thermodynamic driving force for photoexcited charge transfer from quantum dots (QDs) and explore how this affects charge transfer rates, since the efficiency of QD-based photovoltaic and photocatalysis technologies depends on both this rate and the associated energetic losses. In this work, we introduce a single-pot shell growth and Cu-catalyzed cation exchange method to synthesize CdxZn1-xSe/CdyZn1-yS QDs with tunable driving forces for electron transfer. Functionalizing them with two molecular electron acceptorsnaphthalenediimide (NDI) and anthraquinone (AQ)allowed us to probe nearly 1 eV of driving forces. For AQ, at lower driving forces, we find that higher Zn content results in a 130-fold increase of electron transfer rate constants. However, at higher driving forces electron transfer dynamics are unaltered. The data are understood using an Auger-assisted electron transfer model and analyzed with computational work to determine approximate binding geometries of these electron acceptors. Our work provides a method to tune QD reducing power and produces useful metrics for optimizing QD charge transfer systems that maximize rates of electron transfer while minimizing energetic losses.

Automated summary

This study introduces a method to control the thermodynamic driving force for photoexcited charge transfer in quantum dots (QDs) and investigates the electron transfer rates using functionalized QDs. The findings contribute to optimizing charge transfer systems by maximizing the electron transfer rate while minimizing energetic losses.