  Quantum-dot light-emitting diodes (QLEDs) promise high-performance and
cost-effective electroluminescent devices. However, shelf stability of QLEDs, a
must for practical applications, is currently overlooked. Here we reveal that
the state-of-the-art QLEDs exhibit abnormal shelf-ageing behaviours, i.e.,
improvements in performance (positive ageing), followed by deterioration of
performance (negative ageing). Mechanism studies show that the organic acids in
the encapsulation acrylic resin induce in-situ reactions, which simultaneously
improve electrical conductance and minimize interfacial exciton quenching at
the positive-ageing stage. Progression of the in-situ reactions results in
negative ageing. Inspired by these findings, we design an electron-transporting
bi-layer structure, which delivers both improved electrical conductivity and
suppressed interfacial exciton quenching. This design enables shelf-stable
QLEDs with high operational performance, i.e., neglectable changes of external
quantum efficiency (>20.0%) and ultra-long operational lifetime (T95: 5,500
hours at 1,000 cd m-2) after storage for 180 days. Our work paves the way
towards the commercialization of QLEDs.

Applied Physics;Chemical Physics;Optics