Transient electroluminescence from hole transporting emitting layer in nanosecond region

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Abstract
Transient electroluminescence(EL) for an organic thin film cell with a hole transporting emitting layer was observed by short voltage pulse measurements. For the cell with indiumtin oxide/hole transporting emitting layer/Mg:Ag structure, we realized very fast response at a time about 20 ns. This response time has been the fastest in organic EL ever reported. In these measurements, we could observe carrier transit time. We found that this carrier transit time was attributed to that of holes in the emitting layer. The hole mobility in 120‐nm‐thick emitting layer was obtained to be 1±0.3×10−3 cm2/V s in the electric field region from 1 to 3 MV/cm. Furthermore, we could observe the fast EL decay component with a time constant of 3.0±1.5 ns, which was essentially attributed to the decay of singlet excited states.