Development of Zinc Chalcogenide Based Shell Layers for Colloidal Quantum Wells

Two-dimensional colloidal quantum wells have emerged as a promising class of materials for light-emitting devices due to their distinct excitonic properties, including narrow emission linewidths, suppressed Auger recombination, and directional emission. These properties are poised to enhance color quality, brightness, and efficiency in light-emitting devices. However, the commonly studied core/shell heterostructures employing cadmium sulfide shells, present limitations such as quasi type II electronic structures and incomplete electronic passivation for electrons. To address these challenges, we have developed a novel synthetic approach for the growth of zinc chalcogenide-based shell layers for colloidal quantum wells. Our initial investigations focused on the growth of ZnSe shell layers on CdSe colloidal quantum wells having a four-monolayer thickness. These newly synthesized core/shell quantum wells exhibit emission in the range of 620-630 nm with a remarkably narrow emission linewidth of approximately 20 nm. Furthermore, we synthesized core/shell quantum wells terminated with ZnS shell layers for improved surface passivation. These colloidal quantum wells, featuring a graded ZnSexS1-x shell layer, demonstrated a significantly enhanced photoluminescence quantum yield exceeding 85% by preserving their narrow emission linewidth. Finally, we assessed the performance of these newly synthesized colloidal quantum wells in light-emitting devices. Colloidal quantum wells with graded shell structures outperformed those with bare ZnSe shells, achieving an external quantum efficiency of 8.8%. Our findings highlight the potential of zinc chalcogenide shell layers to enhance the performance of colloidal quantum wells, paving the way for advanced light-emitting devices with superior efficiency and color quality.<br/><br/>This study was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the grant no. 123E391 and partially supported by Research Fund of the Middle East Technical University under the project no. 11197.