High-efficiency green phosphorescence from spin-coated single-layer dendrimer light-emitting diodes

Abstract

We demonstrate very high-efficiency green phosphorescence from a single-layer dendrimer organic light-emitting diode formed by spin-coating. A first generation fac-tris(2-phenylpyridine) iridium cored dendrimer doped into a wide-gap 4,4′-bis(N-carbazole) biphenyl host displays a peak external quantum efficiency of 8.1% (28 Cd/A) at a brightness of 3450 Cd/m2 and a current density of 13.1 mA/cm2. A peak power efficiency of 6.9 lm/W was measured at 1475 Cd/m2 and 5 mA/cm2. We attribute this exceptionally high quantum efficiency for a single-layer device to the excellent film forming properties and high photoluminescence quantum yield of the dendrimer blend and efficient injection of charge into the emissive layer. These results suggest that dendrimers are an effective method for producing efficient phosphorescent devices by spin-coating.

Simple color tuning of phosphorescent dendrimer light emitting diodes

“…The emission from both dendrimers is phosphorescence. 5,8 Figure 2 These efficiencies are very much higher than our earlier work 12 on blending blue and blue-green fluorescent dendrimers ͑1.5 lm/ W͒. They are also much higher than the values reported by Kawamura et al 10 for phosphorescent small molecules blended with poly͑9-vinylcarbazole͒ as a host.…”

“…The absorption of both dendrimers in the 350-500 nm wavelength range is due to MLCT transitions and the absorption in the UV region peak- ing at ϳ290 nm is assigned to the biphenyl dendrons and ligands. 5,8,13 Although the difference in absorption is small, there is a substantial difference in the PL spectra, due to a difference in the triplet energy levels of the two materials. The PL spectra of a 20:80 wt % Ir-G1:CBP blend film exhibits a peak at 518 nm with a shoulder at 545 nm.…”

“…We have therefore pursued the development of solution-processible electrophosphorescent dendrimers based on iridium ͑III͒ complexes. [5][6][7] Light-emitting dendrimers consist of a core, dendrons, and surface groups. They have shown great promise, with efficiencies of 55 cd/ A ͑40 lm/ W͒ at 4.5 V and 400 cd/ m 2 reported for two layer green emitting OLEDs 6 while in single layer devices a maximum power efficiency of 12.8 lm/ W at 8.1 V and 550 cd/ m 2 has been observed for the same dendrimer.…”

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

“…4,5,7 These organometallic complexes are highly suitable due to their relatively short excited state lifetime, 7 high photoluminescence efficiencies, and excellent color tunability. 8,9 However, in order to achieve the very good performance, complex device structures are required with several charge transport and exciton confinement layers being used.Solution processible materials such as conjugated polymers 1,2,10 or dendrimers 11,12,13 have also demonstrated high efficiency but in much simpler device structures that can be realized by highly cost effective fabrication techniques such as spin coating 11 and ink-jet printing. 14 We have recently shown that efficient electrophosphorescence can be obtained from single-layer OLEDs employing a solution processible dendrimer compound doped into a suitable host material.…”

“…Solution processible materials such as conjugated polymers 1,2,10 or dendrimers 11,12,13 have also demonstrated high efficiency but in much simpler device structures that can be realized by highly cost effective fabrication techniques such as spin coating 11 and ink-jet printing. 14 We have recently shown that efficient electrophosphorescence can be obtained from single-layer OLEDs employing a solution processible dendrimer compound doped into a suitable host material.…”