Red Phosphorescent Iridium Complex Containing Carbazole‐Functionalized β‐Diketonate for Highly Efficient Nondoped Organic Light‐Emitting Diodes

Abstract

A novel red phosphorescent iridium complex containing a carbazole‐functionalized β‐diketonate, Ir(DBQ)2(CBDK) (bis(dibenzo[f,h]quinoxalinato‐N,C2) iridium (1‐(carbazol‐9‐yl)‐5,5‐dimethylhexane‐2,4‐diketonate)) is designed, synthesized, and characterized. The electrophosphorescence properties of a nondoped device using the title complex as an emitter with a device configuration of indium tin oxide (ITO)/N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐diphenyl‐4,4′‐diamine (NPB; 20 nm)/iridium complex (20 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 5 nm)/tris(8‐hydroxyquinoline) (AlQ; 30 nm)/Mg0.9Ag0.1 (200 nm)/Ag (80 nm) are examined. The results show that the nondoped device achieves a maximum lumen efficiency as high as 3.49 lm W–1. To understand this excellent result observed, two reference complexes Ir(DBQ)2(acac), where acac is the acetyl acetonate anion, and Ir(DBQ)2(FBDK), [bis(dibenzo[f,h]quinoxalinato‐N,C2) iridium (1‐(9‐methyl‐fluoren‐9‐yl)‐6,6‐dimethylheptane‐3,5‐diketonate)], have also been synthesized, and as emitters they were examined under the same device configuration. The maximum lumen efficiency of the former compound is found to be 0.26 lm W–1 while that for the latter is 0.37 lm W–1, suggesting that the excellent performance of Ir(DBQ)2(CBDK) can be attributed mainly to an improved hole‐transporting property that benefits the exciton transport. In addition, a bulky diketonate group separates the emitter centers from each other, which is also important for organic light‐emitting diodes.

Functional IrIII Complexes and Their Applications

“…In our earlier report [11] the novel iridium complex (Fig. 1), was found to be one of the best electrophosphorescent materials in undoped red EL devices to date.…”

“…This leads to a diverse range of emission colors from Ir III complexes. [4][5][6] Thus, Ir III complexes have been widely studied for many applications including organic light-emitting diodes (OLEDs), [7][8][9][10][11] light-emitting electrochemical cells (LECs), [12] luminescence sensitizers, [13,14] biological labeling, [15,16] and chemosensors. [16][17][18][19][20][21] In pursuit of a highly emissive Ir III complex, many heteroleptic complexes of the type [Ir(C^N) 2 MLCT transitions.…”

Advanced Device Architecture for Highly Efficient Organic Light‐Emitting Diodes with an Orange‐Emitting Crosslinkable Iridium(III) Complex

“…Due to the strong spin-orbit coupling of these complexes, both singlet and triplet excitons can be harvested and an internal quantum efficiency of 100 % is possible.[1-3] Many complexes with transition-metals, such as iridium, ruthenium, osmium and platinum have been synthesized to develop highly efficient phosphorescent OLEDs (PHOLEDs), [4][5][6][7][8] because a simple ligand-variation allows for a wide range of emission-colors and for tuning of the chemical properties. …”

“…Typically, in host-guest systems, even at much lower dopant content of other phosphorescent emitter (e.g., 1-5 wt%) no emission of the matrix is observed. [4][5][6][7][8][9][10][11][12][13][14][15][16] We believe that the situation is different here, since the EL-dopant does not constitute a trap for the carriers of the host matrix (here holes), which is usually the case. At higher contents (> 10 wt%) the blue emission of the matrix is entirely suppressed.…”

Properties of materials for organic light emitting diodes

“…70,[124][125][126] Generally though, a small amount of the phosphorescent dye is doped into a host matrix, the purpose of which is to provide (i) charge transport and (ii) prevent intermolecular interactions between emitting phosphors. So as to make the back transfer of energy from guest to host unfavourable, the LUMO and triplet energy levels of the host should have a higher higher energy than the guest.…”