High‐Performance Blue Quantum‐Dot Light‐Emitting Diodes by Alleviating Electron Trapping

Abstract Currently, blue quantum‐dot light‐emitting diodes (QLEDs) remain the bottleneck limiting the development of QLED‐based applications. To achieve high‐performance blue QLEDs, poly‐ N ‐vinylcarbazole (PVK) is usually employed as the hole‐transport layer (HTL) to reduce the hole injection barrier. However, fabrication of efficient blue QLEDs with PVK HTL remains challenging and empirical/accidental. Here, it is demonstrated that PVK layer can trap electrons and hence resulting in low device efficiency. This is why the performance of blue QLEDs is highly dependent on the PVK batch received from the manufacturers. As an interlayer, ZnSe/ZnS quantum dots (QDs) are inserted between PVK and blue ZnCdSe/ZnS QD emitters. The resulted device presents an external quantum efficiency of 20.6% under 2920 cd m −2 , enhanced by ≈35% compared with that of PVK‐alone device. The remarkable enhancement is owing to the QD interlayer that not only suppresses the electron trapping in PVK, increasing the probability of exciton recombination within the emissive layer, but also facilitates the hole injection, improving the charge balance in blue devices.