Solution‐Processible Multi‐component Cyclometalated Iridium Phosphors for High‐Efficiency Orange‐Emitting OLEDs and Their Potential Use as White Light Sources

Abstract

The synthesis and photophysical studies of several multifunctional phosphorescent iridium(III) cyclometalated complexes consisting of the hole‐transporting carbazole and fluorene‐based 2‐phenylpyridine moieties are reported. All of them are isolated as thermally and morphological stable amorphous solids. Extension of the π‐conjugation through incorporation of electron‐pushing carbazole units to the fluorene fragment leads to bathochromic shifts in the emission profile, increases the highest occupied molecular orbital levels and improves the charge balance in the resulting complexes because of the propensity of the carbazole unit to facilitate hole transport. These iridium‐based triplet emitters give a strong orange phosphorescence light at room temperature with relatively short lifetimes in the solution phase. The photo‐ and electroluminescence properties of these phosphorescent carbazolylfluorene‐functionalized metalated complexes have been studied in terms of the coordinating position of carbazole to the fluorene unit. Organic light‐emitting diodes (OLEDs) using these complexes as the solution‐processed emissive layers have been fabricated which show very high efficiencies even without the need for the typical hole‐transporting layer. These orange‐emitting devices can produce a maximum current efficiency of ∼ 30 cd A–1 corresponding to an external quantum efficiency of ∼ 10 % ph/el (photons per electron) and a power efficiency of ∼ 14 lm W–1. The homoleptic iridium phosphors generally outperform the heteroleptic counterparts in device performance. The potential of exploiting these orange phosphor dyes in the realization of white OLEDs is also discussed.

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[182] Another important factor is the dopant concentration in the single layers. [184] Phosphorescent dopant concentrations in WOLEDs range between 0.5 and 11 wt%, whereas the requirements are in general lower for the green and blue dopants, respectively. [183,199,[207][208][209][210] Generally, the layout of the EML ranges between 25 and 40 nm.…”

“…[184,193] Vapor deposition is a very accurate process that allows designing complicated structures by applying mask techniques, but it is also rather intricate, expensive, and limited to the handling of small and thermally stable molecules. In contrast, solution processing techniques are rather low-priced, easily applicable to large areas, and much less restricted regarding the processed materials.…”

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

“…[45] On the other hand, due to the complication and high cost of vacuum deposition which is often used to fabricate small molecule based phosphorescent OLEDs, solution processing offers a lower cost approach to large-area full color displays. [46,47] The synthesis of different generation dendrimers to control their molecular sizes, and thus improve their performance in phosphorescent OLEDs, is a great challenge. [48] Suitable dendrimer size can not only prevent the interaction among the emissive cores but also avoid significant reduction in CT and H. J. Jiang Figure 5.…”

Synthesis, Photophysical and Electrochemical Characterization of the Heteroleptic Iridium Complexes with Modified Ancillary Ligand by Carrier‐transporting Groups

“…Either aryl-oxadiazole or triarylamine units were incorporated into cyclometalated ligands or ancillary ligands by a conjugated connection, and the resulting heteroleptic iridium complexes have displayed improved optoelectronic properties. [3][4][5][6][7][8] However, few of the iridium complexes with bipolar-transporting groups were reported, in which both aryl-oxadiazole and triarylamine units were simultaneously introduced into cyclometalated iridium complexes. 9 In order to further study influence of the carriertransporting groups on optophysical and electrochemical properties of their iridium complexes, we here reported two new iridium complexes with hole-transporting group of triphenylamine or bipolar-transporting groups of triphenylamine and phenyl-oxadiazole.…”