Aldemir, Cagatay HanYazici, Ahmet FarukErgezer, NehirKorkmaz, Taha CanMutlugun, EvrenKelestemur, Yusuf2025-09-252025-09-2520252196-7350https://doi.org/10.1002/admi.202500120https://hdl.handle.net/20.500.12573/4985Colloidal quantum wells, also known as colloidal nanoplatelets (NPLs), have emerged as a promising class of materials for light-emitting devices (LEDs). However, the most widely studied core/shell NPLs, which rely on cadmium-based shell layers, face challenges due to toxicity concerns and improper charge confinement. To address these limitations, a new synthetic approach is presented that enables the controlled growth of zinc chalcogenide-based shell layers on NPLs. The synthesized CdSe/ZnSe core/shell NPLs exhibit emission between 615 and 630 nm, with a moderate photoluminescence quantum yield (PL-QY) of 40-50%. It is also demonstrated that the lateral dimensions of the CdSe core NPLs significantly affect the optical properties of the core/shell heterostructures, with smaller lateral dimensions resulting in narrower emission linewidths as low as 20 nm. Further passivation of these core/shell NPLs with an additional ZnS shell layer significantly increases the PL-QY up to 80-90%. Finally, the device performance of these two core/shell NPLs is investigated by fabricating solution-processed LEDs. With LEDs incorporating CdSe/ZnSe/ZnS core/multi-shell NPLs as the active light-emitting layer, an external quantum efficiency (EQE) of 3.82% and a maximum brightness of 6477 cd m-2 is obtained. These findings underscore the significant potential of zinc chalcogenide-based shell layers in advancing colloidal NPLs toward high-performance light-emitting devices.eninfo:eu-repo/semantics/openAccessColloidal NanoplateletsColloidal Quantum WellsColloidal Semiconductor NanocrystalsCore Shell HeterostructuresLight-Emitting DevicesArticle10.1002/admi.2025001202-s2.0-105003802255