Polyethylenimine Insulativity-Dominant Charge-Injection Balance for Highly Efficient Inverted Quantum Dot Light-Emitting Diodes,ACS Applied Materials & Interfaces

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Polyethylenimine Insulativity-Dominant Charge-Injection Balance for Highly Efficient Inverted Quantum Dot Light-Emitting Diodes
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2017-05-19 00:00:00 , DOI: 10.1021/acsami.7b04662
Ke Ding ₁ , Hongting Chen ₁ , Lianwei Fan ₁ , Bo Wang ₁ , Zhi Huang ₁ , Shaoqing Zhuang ₁ , Bin Hu ₁ , Lei Wang ₁

Affiliation

Quantum dot (QD) light-emitting diodes (QLEDs) with an inverted architecture suffer from charge-injection imbalance and severe QD charging, which degrade device performance. Blocking excess electron injection into QDs is crucial for efficient inverted QLEDs. It is observed that polyethylenimine (PEI) has two opposite effects on electron injection: one is blocking electron injection by its intrinsic insulativity and the other one is promoting electron injection by reducing the work function of ZnO/PEI. In this work, the insulating nature of PEI has been dominantly utilized to reduce electron injection and the charge-injection balance is realized when PEI becomes thicker and blocks more excess electrons. Furthermore, PEI contributes to QD charging suppression and results in a smoother surface morphology than that of ZnO nanoparticles, which is beneficial for leakage current reduction and QD deposition. As a result, the optimized QLED with 15 nm PEI shows a 2.5 times improved efficiency compared to that of the QLED without PEI. Also, the QLED possesses the maximum external quantum efficiency and current efficiency of 16.5% and 18.8 cd/A, respectively, accompanied with a low efficiency roll-off of 15% at 1000 cd/m², which is comparable to that of the reported inverted red QLED with the highest efficiency.

中文翻译：

高效反向量子点发光二极管的聚乙烯亚胺绝缘性占主导地位的电荷注入平衡

具有倒置结构的量子点（QD）发光二极管（QLED）遭受电荷注入不平衡和严重的QD充电，这会降低器件性能。阻止过量的电子注入QD对于有效的倒置QLED至关重要。观察到聚乙烯亚胺（PEI）对电子注入有两个相反的影响：一个是通过其固有的绝缘性阻止电子注入，另一个是通过降低ZnO / PEI的功函数来促进电子注入。在这项工作中，主要利用PEI的绝缘性来减少电子注入，并且当PEI变得更厚并阻止更多的过量电子时，便实现了电荷注入平衡。此外，PEI有助于抑制QD带电，并导致表面形貌比ZnO纳米颗粒更光滑，这有利于减少漏电流和QD沉积。结果，与不具有PEI的QLED相比，具有15 nm PEI的优化QLED的效率提高了2.5倍。此外，QLED的最大外部量子效率和电流效率分别为16.5％和18.8 cd / A，在1000 cd / m时具有15％的低效率滚降参见图²，其与报道的具有最高效率的倒置红色QLED相当。

更新日期：2017-06-03

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