ABSTRACT

This paper provides the sixth manifestation of a new tradition by which the editors of Comments on Inorganic Chemistry wish to lead by example, whereby we start publishing original research content that, nonetheless, preserves the Journal’s identity as a niche for critical discussion of contemporary literature in inorganic chemistry. (For the previous manifestations, see: Comments Inorg. Chem. 2018, 38, 1–35; 2019, 39, 1–26; 2019, 39, 188–215; 2020, 40, 1–24; 2020, 40, 277–303.) Coordination compounds are responsible for multiple quantum leaps in the performance of organic light-emitting diodes (OLEDs). The first breakthrough was via the green-fluorescent main-group complex tris-(8-hydroxyquinoline)aluminum (Alq₃) which acts as both light-emitting and electron-transporting material in combination with triarylamine as a hole-transporter. To optimize the performance of such standard bilayer devices, herein we provide a double-doped structure into the emissive region consisting of 20 nm N,N’-diphenyl-N,N’-bis(1,1ʹ-biphenyl)-4,4ʹ-diamine (NPB) and 10 nm Alq₃ utilized as buffer layers for facilitating charge injection from the electrodes, and a broad emissive region stacked by two doped layers with a 5% Alq₃ doped in a 50-nm thick NPB layer – as well as a 5% NPB doped in a 40-nm-thick Alq₃ layer from the anode side to the cathode side. The double-doped device achieves a decreased turn-on voltage of 2.44 V and maximum brightness of 17,300 cd/m² as well as enhanced electroluminescence efficiency and moderately reduced efficiency roll-off over single-doped and standard bilayer devices. We have also found ~50% improvement of the photoluminescence quantum yield, with some subtle color shift upon doping 10% of NPB or Alq₃ into the other vs. neat Alq₃ (~0.3 vs. ~0.2 ${\varphi }_{PL}$) which nonetheless led only to ~20% improvement in EQE (~1.0% vs. ~0.8%), suggesting additional device optimization is warranted. Furthermore, two typical fluorescent OLEDs architectures – a graded or uniformly mixed device – have been exploited, which together with the double-doped approach would be feasible to boost EL efficiencies in both fluorescent and phosphorescent OLEDs with neat bilayer structures. The approach is not suitable for the more common doped phosphorescent devices, the optimization of which has been reviewed earlier by Nazeeruddin and coworkers in this Journal (Comments Inorg. Chem. 2017, 37, 117–145); in combination with this article, we hope that the reader will have an educational experience on OLED design and optimization from an inorganic chemistry perspective vis-à-vis a materials science perspective that dominates the OLED literature.

摘要

这篇论文提供了一种新传统的第六种表现形式，Comments on Inorganic Chemistry的编辑希望以身作则，我们开始发表原创的研究内容，尽管如此，仍保留了该杂志作为对当代文学进行批判性讨论的利基市场的身份。无机化学。（对于之前的表现形式，请参见：Comments Inorg. Chem . 2018 , 38 , 1-35; 2019 , 39 , 1-26; 2019 , 39 , 188-215; 2020 , 40 , 1-24; 2020 , 40, 277–303.) 配位化合物导致有机发光二极管 (OLED) 性能的多次飞跃。第一个突破是通过绿色荧光主族络合物三-(8-羟基喹啉)铝(Alq ₃ ) 与三芳胺结合作为空穴传输剂的发光和电子传输材料。为了优化此类标准双层器件的性能，我们在发射区提供了一种双掺杂结构，由 20 nm N,N' -diphenyl- N,N' -bis(1,1ʹ-biphenyl)-4,4ʹ -二胺 (NPB) 和 10 nm Alq ₃用作缓冲层以促进来自电极的电荷注入，以及由两个掺杂层堆叠而成的宽发射区域，其中 5% Alq ₃掺杂在 50 nm 厚的 NPB 层中 - 以及 5% NPB 掺杂在 40 nm 厚的 NPB 层中从阳极侧到阴极侧的nm厚的Alq _3层。双掺杂器件实现了 2.44 V 的降低开启电压和 17,300 cd/m ²的最大亮度以及增强的电致发光效率和适度降低了单掺杂和标准双层器件的效率滚降。我们还发现光致发光量子产率提高了约 50%，在将 10% 的 NPB 或 Alq ₃掺杂到另一个与. 整洁的 Alq ₃（~0.3对.~0.2${\phi }_{磷\mathrm{大号}}$) 但仅导致 EQE 提高约 20%（约 1.0%与约 0.8%），这表明有必要进行额外的设备优化。此外，已经开发了两种典型的荧光 OLED 架构——渐变或均匀混合的器件，与双掺杂方法一起提高具有整洁双层结构的荧光和磷光 OLED 的 EL 效率是可行的。该方法不适用于更常见的掺杂磷光器件，Nazeeruddin 和他的同事早先已在本期刊中对其优化进行了审查（评论 Inorg. Chem . 2017 , 37, 117–145); 结合本文，我们希望读者能够从无机化学的角度与主导 OLED 文献的材料科学的角度对 OLED 设计和优化进行教育体验。