Performance Enhancement of Cadmium-Free Quantum-Dot Light-Emitting Diodes via Cl-Passivated Zn1−x−ySnxMgyO Nanoparticles as Electron Transport Layers

Although cadmium (Cd)-based nanocrystals have enabled high-performance quantum-dot light-emitting diodes (QLEDs), their mass production is likely to be affected by environmental protection policies. Among all the potential Cd-free candidates, Cu-In-Zn-S (CIZS) nanocrystals (NCs) have attracted particular interests. Still, the performance of the corresponding LED is currently limited by imbalanced charge injection and luminescence quenching, which are both related to the ZnO-based electron transporting layer (ETL). This work demonstrates that ZnO nanoparticles (NPs) doped with Sn, Mg (Zn 1− x − y Sn x Mg y O), and passivated with Cl are promising to resolve the above issues. All-solution-processed QLEDs based on Cd-free CIZS NCs are fabricated by using Zn 0.9 Sn 0.1 O NPs as the ETL, and the peak external quantum efficiency (EQE max ) was nearly twice that of ZnO (EQE max = 1.74%). The main reason is that the incorporation of Sn can reduce the conductivity of ZnO by an order of magnitude. Combining the advantages of Zn 0.9 Sn 0.1 O, Zn 0.8 Sn 0.1 Mg 0.1 O@Cl NPs are designed by the co-doping of Mg and Cl passivation. The EQE max and current efficiency based on Zn 0.8 Sn 0.1 Mg 0.1 O and Zn 0.8 Sn 0.1 Mg 0.1 O@Cl as ETLs are further increased to 4.84%, 14.00 cd A −1 and 5.53%, 15.99 cd A −1 , respectively. The positive effects of Mg ions can remarkably optimize energy level structure to balance charge injection, while Cl can further passivate defects. The findings offer a new guideline for developing Cd-free light-emitting diodes.