High-efficiency red electrophosphorescence devices

We demonstrate high-efficiency red electrophosphorescent organic light-emitting devices employing bis(2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C³′) iridium(acetylacetonate) [Btp₂Ir(acac)] as a red phosphor. A maximum external quantum efficiency of η_ext=(7.0±0.5)% and power efficiency of η_p = (4.6±0.5) lm/W are achieved at a current density of J=0.01 mA/cm². At a higher current density of J=100 mA/cm², η_ext=(2.5±0.3)% and η_p=(0.56±0.05) lm/W are obtained. The electroluminescent spectrum has a maximum at a wavelength of λ_max=616 nm with additional intensity peaks at λ_sub=670 and 745 nm. The Commission Internationale de L'Eclairage coordinates of (cursive Greek chi=0.68, y=0.32) are close to meeting video display standards. The short phosphorescence lifetime (∼4 μs) of Btp₂Ir(acac) leads to a significant improvement in η_ext at high currents as compared to the previously reported red phosphor, 2,3,7,8,12,13,17,18-octaethyl-12H, 23H-prophine platinum (II) PtOEP with a lifetime of ∼50 μs.