Balancing charge injection in quantum dot light-emitting diodes to achieve high efficienciy of over 21%

Quantum dot light-emitting diodes (QLEDs) have attracted considerable attention in displays owing to their high color purity, wide gamut, narrow emission band, and solution-processed characteristics. However, a major problem of the unbalanced carrier (electrons holes) injection QLEDs deteriorates performance. Here, we balanced charge by optimizing transport layers. Different organic hole layers (HTLs) with suitable thickness were employed match electron layer (ETL) ZnO. Mg2+ was doped into ZnO (MZO) ETL decrease mobility HTL. Consequently, exhibited an excellent external quantum efficiency (EQE) 21.10% at luminance 4661 cd m−2. In range 100–30,000 m−2, EQE roll-off considerably low, more than 80% initial value could be maintained, indicating less Auger recombination because injection. This work reveals that compared energy level matching, transfer capability is instrumental balance regulation QLED devices.