Highly efficient molecular organic light-emitting diodes based on exciplex emission

Highly efficient exciplex emission is observed from molecular organic light-emitting diodes (MOLEDs) based on silole derivatives as emissive and electron transport materials, and a hole transporting amine derivative. A silole derivative, 2,5-di-(3-biphenyl)-1,1-dimethyl- 3,4-diphenylsilacyclopentadiene (PPSPP), which shows blue fluorescence (476 nm) with a high solid-state photoluminescence quantum yield of 85% was used as the emitter. Another silole derivative, $\text{2,5-}\mathrm{bis}{\text{-(2}}^{\prime }{\text{,2}}^{″}-\mathrm{bipyridin}\text{-6-}\mathrm{yl}\text{)-1,1-}\mathrm{dimethyl}\text{-3,4-}\mathrm{diphenylsilacyclopentadiene}$ which exhibits high electron mobility, was used as the electron transport material. MOLEDs using these two siloles and ${\mathrm{N,N}}^{\prime }-{\mathrm{diphenyl-N,N}}^{\prime }\text{-(2-}\mathrm{napthyl}{\text{)-(1,1}}^{\prime }-\mathrm{phenyl}{\text{)-4,4}}^{\prime }-\mathrm{diamine}$ (NPB) as the hole transporter show electroluminescence (EL) emission centered at 495 nm. This red-shifted EL band relative to the blue fluorescence of PPSPP is assigned to a NPB:PPSPP exciplex. An operating voltage of 4.5 V was measured at $\text{100\hspace{0.17em}}{\mathrm{cd/m}}^2$ and an EL quantum efficiency of 3.4% was achieved at $\text{100\hspace{0.17em}}{\mathrm{A/m}}^2.$