Chen Fei, Wang Li-Jin, Li Xu, Deng Zhen-Bo, Teng Feng, Tang Ai-Wei
Opt Express. 2020 Mar 2;28(5):6134-6145. doi: 10.1364/OE.386276.
The search for heavy-metal-free quantum-dot light-emitting diodes (QD-LEDs) has greatly intensified in the past few years because device performance still falls behind that of CdSe-based QD-LEDs. Apart from the effects of nanostructures of the emitting materials, the unbalanced charge injection and transport severely affects the performance of heavy-metal-free QD-LEDs. In this work, we presented solution-processed double hole transport layers (HTLs) for improving the device performance of heavy-metal-free Cu-In-Zn-S(CIZS)/ZnS-based QD-LEDs, in which N,N'-Bis(3-methylphenyl)-N,N'-bis(phenyl)benzidine (TPD) as an interlayer was incorporated between the emitting layer and the HTL. Through optimizing the thickness of poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenyl-amine (TFB) and TPD layers, a maximum external quantum efficiency (η) of 3.87% and a current efficiency of 9.20 cd A were achieved in the solution-processed QD-LEDs with double-layered TFB/TPD as the HTLs, which were higher than those of the devices with pristine TFB, TPD and TFB:TPD blended layers. The performance enhancement could be attributed to the synergistic effects of the reduction of the hole injection barrier, the increase of the hole mobility and suppressed charge transfer between the HTL and the emitting layer. Furthermore, the best η of 5.61% with a mean η of 4.44 ± 0.73% was realized in the Cu-In-Zn-S-based QD-LEDs by varying the annealing temperature of TPD layer due to the more balanced charge injection and transport as well as smooth surface of TPD layer.
在过去几年中，对无重金属量子点发光二极管（QD-LED）的研究力度大幅加大，因为其器件性能仍落后于基于CdSe的QD-LED。除了发光材料纳米结构的影响外，电荷注入和传输不平衡严重影响了无重金属QD-LED的性能。在这项工作中，我们展示了用于改善无重金属Cu-In-Zn-S（CIZS）/ZnS基QD-LED器件性能的溶液处理双空穴传输层（HTL），其中在发光层和HTL之间引入了N，N'-双（3-甲基苯基）-N，N'-双（苯基）联苯胺（TPD）作为中间层。通过优化聚（9,9-二辛基芴-co-N-（4-丁基苯基）二苯胺（TFB）和TPD层的厚度，在以双层TFB/TPD作为HTL的溶液处理QD-LED中实现了3.87%的最大外量子效率（η）和9.20 cd/A的电流效率，高于具有原始TFB、TPD和TFB:TPD混合层的器件。性能的提高可归因于空穴注入势垒降低、空穴迁移率增加以及HTL与发光层之间电荷转移受到抑制的协同效应。此外，通过改变TPD层的退火温度，在基于Cu-In-Zn-S的QD-LED中实现了5.61%的最佳η，平均η为4.44±0.73%，这是由于电荷注入和传输更加平衡以及TPD层表面光滑。
