Homogeneous ZnSeTeS quantum dots for efficient and stable pure-blue LEDs.

The electroluminescence performance of heavy-metal-free blue quantum dot (QD) light-emitting diodes (QLEDs) is much lower than that of state-of-the-art cadmium-based counterparts. Ecofriendly ZnSeTe QDs are an ideal alternative to cadmium-based blue QDs, but face issues with colour impurity and inferior stability caused by the aggregated tellurium (Te) that dominates compositional inhomogeneity. Here we developed an isoelectronic control strategy using congeneric sulfur coordinated with triphenyl phosphite (TPP-S) to construct homogeneous ZnSeTeS QDs with pure-blue emissions and near-unity photoluminescence quantum yield. TPP with low electron-donating capability promotes the reactivity balance among anionic precursors, favouring the growth of QDs with uniform composition. The acceptor-like S with high electronegativity weakens the hole localization of the Te atoms by interfering with their surrounding carriers, thereby suppressing the formation of Te isoelectronic centres. Furthermore, the congeneric S increases the configurational entropy of the QDs and eliminates the stacking faults and oxygen defects, leading to improved structural stability and reduced non-radiative carrier density. Consequently, the resulting pure-blue QLEDs based on core-shell ZnSeTeS/ZnSe/ZnS QDs emitting at 460 nm show a high external quantum efficiency of 24.7%, a narrow linewidth of 17 nm, and long operational half-lifetime (T) close to 30,000 hours at 100 cd cm, rivalling state-of-the-art cadmium-based blue QLEDs.