  Colloidal quantum dots (QDs) are promising emitters for electroluminescence
devices (QD light-emitting-diodes, QLEDs). Though QDs have been synthesized
with efficient and stable photoluminescence, inheriting their superior
luminescence in QLEDs remains challenging. This is commonly attributed to
unbalanced charge injection and/or interfacial exciton quenching in the
devices, instead of lack of suited QD materials. Here, a general but previously
overlooked degradation channel in QLEDs, i.e., operando electrochemical
reactions of surface ligands with injected charge carriers, is identified after
systematic studies of various combination of core/shell QDs and ligands.
Applying electrochemically-inert ligands to highly photoluminescent QDs is
developed to bridge their photoluminescence-electroluminescence gap. This
material-design principle is general for boosting electroluminescence
efficiency and lifetime of the QLEDs, resulting in record-long operational
lifetimes for both red-emitting QLEDs (T95 > 3800 hours at 1000 cd m-2) and
blue-emitting QLEDs (T50 >10,000 hours at 100 cd m-2). Our study provides a
critical guideline for the QDs to be used in optoelectronic and electronic
devices.
