Bandgap- and Mobility-Tunable ZnxCd1–xS Alloy Nanoparticles as Electron Transport Layers for High-Performance Inverted Quantum Dot Light-Emitting Diodes

Colloidal quantum dot light-emitting diodes (QLEDs) typically rely on ZnO-based electron transport layers (ETLs), which often suffer from excessive electron injection and an undesirable positive aging effect. Herein, we demonstrate a new class of ZnxCd1–xS alloy nanocrystals as bandgap- and mobility-tunable ETLs for inverted QLEDs. By varying the Zn/Cd ratio, the optical bandgap of the ZnxCd1–xS nanocrystals can be continuously tuned from 2.52 to 3.85 eV, enabling precise alignment of the conduction band minimum with the quantum dot emissive layer. Furthermore, an in situ ligand exchange with 3-mercaptopropionic acid (MPA) is employed to replace the long-chain insulating oleylamine ligand, significantly enhancing the film conductivity by nearly 2 orders of magnitude. MPA-treated Zn0.1Cd0.9S-based QLED achieves a maximum external quantum efficiency of 16.4% and a peak luminance of 139,937 cd m–2, representing an ∼93% enhancement over the untreated device. This work establishes composition- and ligand-engineered ZnxCd1–xS alloy nanocrystals as versatile and efficient ETL platforms for next-generation QLEDs.