Off-State-Free and Stable InP/ZnSe/ZnS Quantum Dots Enabled by Effectively Suppressing the Leakage of Charge Carriers

Reaction crude solutions of colloidal semiconductor nanocrystal quantum dots (QDs) contain various impurities. To use QDs in optoelectronic devices or store them, the impurities must be removed through purification procedures. However, the purification steps often result in the creation of electronic traps because surface ligands are partially removed during purifications. Hence, maintaining the original quality of the QDs after purification is very challenging. Herein, we present a strategy to preserve the original quality of InP/ZnSe/ZnS QDs by engineering the charge carrier wavefunctions. By introducing a thick ZnS shell layer, we effectively confine the charge carrier wavefunctions inside the InP/ZnSe/ZnS QDs because the thick ZnS layer acts as a large electronic barrier. Consequently, we obtain high-quality InP/ZnSe/ZnS QDs with a suppressed photoluminescence quantum yield (PL QY) drop, whereas InP/ZnSe/ZnS QDs with thin ZnS shell layers experience a considerable decrease in their PL QY after multiple purification steps. Time-resolved photoluminescence and single dot spectroscopy studies demonstrate that InP/ZnSe/ZnS QDs with a properly thick ZnS shell are significantly less affected by surface traps due to the reduced leakage of charge carriers. Theoretical understanding based on wavefunction calculations also supports this observation. Our strategy offers a promising way to maintain the optoelectronic properties of QDs during purification procedures, thereby enhancing their potential for various applications.