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Carrier imbalance resulting from stronger electron injection from ZnO into quantum-dot (QD) emissive layer than hole injection is one critical issue that constrains the performance of QDs-based light-emitting diodes (QLEDs). This study reports highly efficient inverted QLEDs enabled by periodic insertion of MoO 3 into (4,4′-bis(N-carbazolyl)-1,1′-biphenyl) (CBP) hole transport layer (HTL). The periodic ultrathin MoO 3 /CBP-stacked HTL results in improved lateral current spreading for the QLEDs, which significantly relieves the crowding of holes and thus enhances hole transport capability across the CBP in QLEDs. Comprehensive analysis on the photoelectric properties of devices shows that the optimal thickness for MoO 3 interlayer inserted in CBP is only ≈1 nm. The resulting devices with periodic two insertion layers of MoO 3 into CBP exhibit better performance compared with the CBP-only ones, such that the peak current efficiency is 88.7 cd A −1 corresponding to the external quantum efficiency of 20.6%. Furthermore, the resulting QLEDs show an operational lifetime almost 2.5 times longer compared to CBP-only devices.

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In this work, we simply take advantage of the polarization effect to efficiently improve the hole injection from the p-type electron blocking layer (p-EBL) to the end of the active region for AlGaN based deep ultraviolet light emitting diodes (DUV LEDs). By properly increasing the AlN composition of AlGaN quantum barriers, a smaller positive polarized charge density at the last quantum barrier/p-EBL interface can be obtained, which correspondingly leads to the suppressed hole depletion and the reduced hole blocking effect in the p-EBL. Meanwhile, we properly increase the quantum well thickness so that the polarized electric field can even more accelerate the holes, and this will homogenize the hole distribution more across the MQWs. Therefore, the external quantum efficiency for DUV LEDs can be enhanced.