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 $ηext=(7.0±0.5)%$ and power efficiency of $ηp=(4.6±0.5) lm/W$ are achieved at a current density of $J=0.01 mA/cm2.$ At a higher current density of $J=100 mA/cm2,$ $ηext=(2.5±0.3)%$ and $ηp=(0.56±0.05) lm/W$ are obtained. The electroluminescent spectrum has a maximum at a wavelength of $λmax=616 nm$ with additional intensity peaks at $λsub=670$ and 745 nm. The Commission Internationale de L’Eclairage coordinates of $(x=0.68,$ $y=0.32)$ are close to meeting video display standards. The short phosphorescence lifetime (∼4 μs) of $Btp2Ir(acac)$ leads to a significant improvement in $ηext$ 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.