Quantum dot light-emitting diodes (QLEDs) are attractive to be used for new generation displays since their advantages of high color saturation and emission efficiency. However, the wide-bandgap blue light-emitting quantum dots (QLEDs) suffer from an undesirable emission from surface defects of ZnO nanoparticles which are widely used as an electron transport layer (ETL). Here, we firstly present an inverted structure of blue QLEDs with inserting an ultra-thin layer of polyethylenimine (PEI) between the ITO and ZnO layer to address such issue. The QLEDs with the inverted structure of ITO/PEI/ZnO/QDs/PVK/MoO₃/Al (where PVK is poly (N-vinylcarbazole)) exhibit a pure blue emission with the CIE color coordinates of (0.14, 0.04). Meanwhile, the peak external quantum efficiency (EQE) of the blue QLEDs increases from 3.5% to 5.5%. The improved color purity and efficiency are attributed to decreasing oxygen vacancy defects of ZnO and electron accumulation at the interface of ZnO and QDs by means of modifying ZnO nanoparticles with PEI. The results may suggest a potential method of using PEI as the interfacial layer to fabricate high efficiency and pure blue QLEDs.

量子点发光二极管（QLED）具有很高的色彩饱和度和发射效率，因此很适合用于新一代显示器。然而，宽带隙蓝色发光量子点（QLED）遭受被广泛用作电子传输层（ETL）的ZnO纳米颗粒的表面缺陷的不期望的发射。在这里，我们首先提出一种蓝色QLED的倒置结构，在ITO和ZnO层之间插入聚乙烯亚胺（PEI）的超薄层以解决这一问题。具有ITO / PEI / ZnO / QDs / PVK / MoO ₃倒置结构的QLED/ Al（其中PVK为聚（N-乙烯基咔唑））显示纯蓝色发射，CIE颜色坐标为（0.14，0.04）。同时，蓝色QLED的峰值外部量子效率（EQE）从3.5％增加到5.5％。改善的色纯度和效率归因于通过用PEI改性ZnO纳米颗粒，减少了ZnO的氧空位缺陷以及在ZnO和QDs界面上的电子积累。结果可能表明使用PEI作为界面层来制造高效和纯蓝色QLED的潜在方法。