Decoupling Photoinduced Electron Transfer and Trap-Induced Relaxation Kinetics in Colloidal Quantum Dots

Photoinduced electron transfer (PET) in colloidal quantum dots (QDs) is important for solar-energy applications. However, in these systems, interfacial charge transfer competes with intrinsic recombination losses. We investigated PET kinetics in CdSe-based QDs with different shell architectures (CdSe, CdSe/CdS, and CdSe/CdS/ZnS) using anthraquinone as an electron acceptor to study the effects of surface trap-mediated relaxation and tunneling barriers. Inorganic shells effectively suppress trap-mediated nonradiative decay but simultaneously inhibit PET by introducing tunneling barriers and reducing the thermodynamic driving force. Conversely, bare CdSe QDs exhibit intrinsically fast electron transfer but suffer from dominant surface trap-mediated relaxation, limiting PET efficiency. By resolving the distinct contributions, we demonstrate that the surface modification of bare QDs can tune the nonradiative relaxation rate and PET efficiency without the penalty of a tunneling barrier. Therefore, the surface-engineered control of nonradiative decay in shell-free QDs is a critical design parameter for optimizing energy-conversion systems.