All‐Inorganic Quantum Dot Light‐Emitting Diodes with Suppressed Luminance Quenching Enabled by Chloride Passivated Tungsten Phosphate Hole Transport Layers

Abstract Although excellent performance such as high efficiency and stability have been achieved in quantum dot (QD)‐based light‐emitting diodes (QLEDs) possessing an organic/inorganic hybrid device structure, the highly expected all‐inorganic QLEDs remain at the bottleneck stage in recent years, resulting from the luminance quenching of QDs caused by inorganic hole transport layer (HTL) and unbalanced charge injection due to large energy barrier for injecting holes from HTL to QDs. Here, it is reported that the solution‐processed inorganic environmentally friendly chloride (Cl)‐passivated tungsten phosphate (Cl@TPA) films serve as HTL. The incorporation of Cl in TPA effectively passivates the oxygen vacancies, which not only avoids the luminescence quenching of QDs by reducing carrier concentration but also facilitates the hole injection from HTL to QDs with a favorable electronic band alignment, thus achieving the record external quantum efficiency of ≈ 9.27%, among all previous reports about all‐inorganic QLEDs. Most importantly, the resulting all‐inorganic QLEDs with Cl@TPA exhibit a substantial improvement in the operational lifetime ( T 50 > 10 5 h under an initial luminance of 100 cd m −2 ), which is almost 30‐fold higher than the devices with TPA HTL. This work furnishes a promising strategy for highly efficient and stable QLEDs based on inorganic device structure.