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 (Zn1-x-ySnxMgyO), 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 Zn0.9Sn0.1O 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 Zn0.9Sn0.1O, Zn0.8Sn0.1Mg0.1O@Cl NPs are designed by the co-doping of Mg and Cl passivation. The EQE(max) and current efficiency based on Zn0.8Sn0.1Mg0.1O and Zn0.8Sn0.1Mg0.1O@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.