High-efficiency red electrophosphorescence devices

We demonstrate high-efficiency red electrophosphorescent organic light-emitting devices employing ${\text{bis(2-(2}}^{\prime }-{\mathrm{benzo[4,5-a]thienyl)pyridinato-N,C}}^{{\mathrm{3}}^{\mathrm{\prime }}})$ iridium(acetylacetonate) $[{\mathrm{Btp}}_{\mathrm{2}}\mathrm{Ir(acac)}]$ as a red phosphor. A maximum external quantum efficiency of ${\eta }_{\mathrm{ext}}\text{=(7.0±0.5)\%}$ and power efficiency of ${\eta }_p\text{=(4.6±0.5)\hspace{0.05em}}\mathrm{lm/W}$ are achieved at a current density of $\text{J=0.01\hspace{0.05em}}{\mathrm{mA/cm}}^{\mathrm{2}}.$ At a higher current density of $\text{J=100\hspace{0.05em}}{\mathrm{mA/cm}}^{\mathrm{2}},$ ${\eta }_{\mathrm{ext}}\text{=(2.5±0.3)\%}$ and ${\eta }_p\text{=(0.56±0.05)\hspace{0.05em}}\mathrm{lm/W}$ are obtained. The electroluminescent spectrum has a maximum at a wavelength of ${\lambda }_{\max }\text{=616\hspace{0.05em}}\mathrm{nm}$ with additional intensity peaks at ${\lambda }_{\mathrm{sub}}\text{=670}$ and 745 nm. The Commission Internationale de L’Eclairage coordinates of $\text{(x=0.68,}$ $\text{y=0.32)}$ are close to meeting video display standards. The short phosphorescence lifetime (∼4 μs) of ${\mathrm{Btp}}_{\mathrm{2}}\mathrm{Ir(acac)}$ leads to a significant improvement in ${\eta }_{\mathrm{ext}}$ 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.