Delayed electroluminescence via triplet–triplet annihilation in light emitting diodes based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]

A spectroscopically resolved delayed electrofluorescence is observed from $\mathrm{poly}\text{[2-}\mathrm{methoxy}{\text{-5-(2}}^{\prime }$ -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV) thin film at low temperature. From the measurements of the delayed fluorescence intensities at a particular delay time as well as the decay kinetics of the delayed fluorescence spectra at different temperatures, we conclude that the delayed fluorescence is generated via triplet–triplet annihilation. It is suggested that the triplet state of MEH–PPV thin film has a lifetime much shorter than that of polyfluorene thin film, which is consistent with the triplet energies of these polymers.