TRANSIENT ELECTROLUMINESCENCE FROM HOLE TRANSPORTING EMITTING LAYER IN NANOSECOND REGION

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 indium tin oxide/hole transporting em itting 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 ev er reported. In these measurements, we could observe carrier transit t ime. We found that this carrier transit time was attributed to that of holes in the emitting layer. The hole mobility in 120-nm-thick emitti ng layer was obtained to be 1 +/- 0. 3 X 10(-3) CM2/V s in the electri c field region from 1 to 3 MV/cm. Furthermore, we could observe the fa st EL decay component with a time constant of 3.0 +/- 1.5 ns, which wa s essentially attributed to the decay of singlet excited states.