Tetranuclear Iridium Complex with a Self-Host Feature for High-Efficiency Nondoped Phosphorescent Organic Light-Emitting Diodes

Abstract

A tetranuclear Ir complex 3IrB-IrG was newly designed and synthesized with one green-emitting complex as the core, whose periphery is encapsulated by three blue-emitting complexes via a nonconjugated linkage. In the case of such a multinuclear system, a self-host feature can be formed, showing negligible electron communication, efficient outside-in energy transfer, and unique shielding effect. When using 3IrB-IrG as the emitting layer in the absence of host, the corresponding nondoped device reveals a state-of-art luminous efficiency of 32.6 cd/A (34.2 lm/W, 9.7%) as well as CIE coordinates of (0.38, 0.58). The performance significantly outperforms that of the bare mononuclear complex IrG (8.4 cd/A, 9.2 lm/W, 2.5%), highlighting the potential of self-host multinuclear complexes to realize high-efficiency nondoped PhOLEDs for the first time.

Multinuclear Iridium Complex Encapsulated by Oligocarbazole Dendrons for Enhanced Nondoped Device Efficiency

“…Figure 2a depicts the absorption and photoluminescence (PL) spectra in solutions for Cz–3IrB–IrG with 3IrB–IrG as the control. Consistent with the literature, 23 the absorption bands below 325 nm are ascribed to the spin-allowed ligand-centered transitions, whereas the weak bands in the range of 325–500 nm are assigned to the metal-to-ligand and ligand-to-ligand charge-transfer transitions. Compared with the 3IrB–IrG, the sharp enhancement of the absorption coefficient below 325 nm for Cz–3IrB–IrG is reasonable from the incorporation of the peripheral oligocarbazole dendrons.…”

“…18−22 Recently, we have put forward an alternative strategy, namely multinucleation, toward nondoped phosphors. 23 The issued tetranuclear iridium (Ir) complex 3IrB−IrG possesses a characteristic self-host feature similar to phosphorescent dendrimers (Figure 1), where the three outer blue Ir complexes can act as the host for the one inner green Ir core. In addition, the corresponding nondoped device achieves an appealing luminous efficiency as high as 32.6 cd/A.…”

Mechanism study on highly efficient polymer light-emitting diodes utilizing double-layered alkali halide electron injection layer

“…Polymer light-emitting diodes (PLEDs) have absorbed tremendous attentions all over the world because of their attractive application potentials in flat panel display and solid-state lighting 1–3 . Although great progresses have been made on the performance of PLEDs since the first report of efficient PLEDs, there are still some issues have to be addressed 4–6 . One of the urgent issues is to realize efficient electron injection 7,8 to achieve the balance of electron and hole current, which will lead to the enhancement of PLEDs performance 9 .…”

Unravelling Electroplex Emission from Long-Range Charge Transfer Based on a Phosphorescent Dendrimer as the Electron Donor

“…In the past two decades, the replacement of fluorescent materials by phosphorescent ones has attracted extensive attention in both academia and industry owing to the theoretical 100% exciton-harvesting ability. − In particular, compared with the commercialized and expensive vacuum-deposition emitters, − solution-processed compounds exhibit the fascinating characteristics of low cost and large-area processes. − Among three classes of solution-processable emitters, that is, small molecules, − dendrimers, − and polymers, , the dendrimers integrate the merits of both the well-defined structure of small molecules and the good solution processability of polymers. More importantly, the peripheral dendron wrapping around the central core not only can effectively prevent the quenching/aggregation of the emissive cores but also can maintain the intrinsic emissive characteristics.…”

“…More importantly, the peripheral dendron wrapping around the central core not only can effectively prevent the quenching/aggregation of the emissive cores but also can maintain the intrinsic emissive characteristics. It is well known that the carbazole-based substituent is a typical hole-transporting group that has been proverbially introduced as the host shell in the dendrimer emitters. − ,− Recently, Lee’s group verified another promising application of the electroplex. They utilized common carbazole-based hole-transporting materials, for example, 4,4′-di­(9 H -carbazol-9-yl)-1,1′-biphenyl (CBP) and 3,3-di­(9 H -carbazol-9-yl)­biphenyl (mCBP), to integrate with the electron-transporting materials and thus form the electroplex host for red, yellow, green, and blue phosphorescent OLEDs. , Our group has proven that the dendrimer based on the carbazole dendrons has the ability to form an interfacial exciplex with the ETL. , These studies predict that the dendrimer emitters with the carbazole dendrons have a potential possibility of forming an electroplex, which is fairly stable under the electrical field excitation.…”