Efficient organic light-emitting diodes with undoped active layers based on silole derivatives

We report on efficient molecular organic light-emitting diodes (MOLEDs) composed of novel silole derivatives as an electron transporting layer and an emissive layer. The silole derivative, $\text{2,5-}\mathrm{bis}{\text{(2}}^{\prime }{\text{,2}}^{″}$ -bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene, used for the electron transport layer exhibits fast electron mobility of ${\text{2×10}}^{\text{−4}}\hspace{0.17em}{\mathrm{cm}}^2/\mathrm{V s}$ at 0.64 MV/cm measured by the time-of-flight technique. Another silole derivative, 1,2-bis(1-methyl-2,3,4,5-tetraphenyl silacyclopentadienyl)ethane, used for an emissive layer exhibits blue-green fluorescence with an absolute quantum yield of $\text{97±3\%}$ in the solid state. The devices using silole derivatives show a very low operating voltage, an external electroluminescence quantum efficiency ${\mathrm{(\eta }}_{\mathrm{EL}})$ of 4.8 %, and luminous power efficiency of 9 lm/W at a brightness of $\text{100\hspace{0.17em}}{\mathrm{cd/m}}^2.$ This value of ${\eta }_{\mathrm{EL}}$ is the best efficiency achieved for MOLED using undoped emissive and carrier transport layers and is close to the theoretical limit for a device using a fluorescent emitter.