Over 800% Efficiency Enhancement of Solution-Processed All-Inorganic Quantum-Dot Light Emitting Diodes with an Ultrathin Alumina Passivating Layer

The use of robust, inorganic charge-transport materials is always desired in quantum-dot light emitting diodes (QLEDs) because they are expected to allow higher stability and less cost than that of organic counterparts. Here we report an all-inorganic QLED with excellent efficiency by modifying the solution-processed NiO (s-NiO) surface with an ultrathin Al2O3 passivating layer. The localized electric field induced by nickel oxyhydroxide (NiOOH) is estimated to be ~ 70 MV/cm at a distance of 6 nm from the surface of s-NiO layer. Both transient resolution photoluminescence (TRPL) and X-Ray photoelectron spectroscopy (XPS) measurements demonstrate that the Al2O3 passivating layer can effectively passivate the NiOOH on the s-NiO surface, hence suppressing the exciton quenching. As a result, over 800% efficiency enhancement up to 34.1 cd/A (8.1%) for the current efficiency (external quantum efficiency, EQE) of the QLEDs is achieved. To the best of our knowledge, this is the best-performing all-inorganic QLED so far.