Highly Efficient Phosphorescent Green Organic Light-Emitting Diodes with High Energy Gap Host Materials

Abstract

We investigated the electroluminescent characteristics of three devices which were fabricated with a green phosphorescent emitter bis[2-(o-terphen-3-yl)pyridinato-C,N]iridium(III) (acetylacetonate) [(tppy)₂Ir(acac)] doped in triphenylsilane-based host materials, such as 4,4′-bis(triphenylsilyl)biphenyl (BSB), 9,9′-spirobifluorene-2-yltriphenylsilane (SFS) and (4-(10-(naphthalene-2-yl)anthracen-9-yl)phenyl)triphenylsilane (ANPTPS), which have the different the triplet energy levels (E _T) of 2.61 eV, 2.64 eV and <1.91 eV, respectively. Among those, two devices using BSB and SFS hosts with the suitable E _T energy levels to green phosphorescent dopant exhibited the highly efficient green electrophosphorescence with the maximum luminous efficiencies of 51.3 cd/A and 46.6 cd/A, respectively, and the maximum quantum efficiencies of 13.9% and 12.4%, respectively.

Keywords:

• Green phosphorescent host
• organic light-emitting diode
• triphenylsilane
• triplet energy level

Acknowledgments

This work was supported by Energy Resources Technology Development program (2007-E-CM11-P-07) and Strategy Technology Development program (10030834) from Ministry of Knowledge Economy (MKE).

Notes

^a Maximum absorption or emission wavelength, measured in CH₂Cl₂ solution.

^b Phosphorescent emission in 2-methyl-THF solution at 77 K. The triplet energy (E _T) calculated is included in the parenthesis.

^c Obtained from AC-2 and UV-vis absorption measurements.

^d Using DPA as a standard; λ_ex = 360 nm (λ = 0.90 in CH₂Cl₂).

^e not observed up to 650 nm.

^a Maximum current density. At 8.0 V.

^b Maximum luminance. At 9.5 V.

^c Maximum value.

^d At 20 mA/cm².

^e CIE coordinate (x, y) at 8.0 V.

^f Maximum emission wavelength of devices at 8.0 V.