Highly efficient organic light-emitting diodes based on the red phosphorescent emitter sensitized by the green emitting iridium complex

We demonstrated the red phosphorescent organic light-emitting diodes with sensitizer, iridium(III) tris(2-phenylpyridine) [Ir(ppy)3]. The devices with sensitizer showed a significant improvement in a luminance and efficiency compared to those without sensitizer. Moreover, the electroluminescent (EL) spectra of devices with sensitizer show a similar emission peak with photoluminescent (PL) spectra of iridium(III) bis(2-phenylquinoline)(acetylaceton) [Ir(pq)2(acac)] under the optimized doping ratio of Ir(pq)2(acac) and Ir(ppy)3. It is because that the triplet metal-to-ligand charge transfer (³MLCT) state of Ir(ppy)3 is higher than that of Ir(pq)2(acac) and the intra-molecular energy transfer (IMET) time (within ns time scale) from the ppy-centered ³MLCT state to the pq-centered ³MLCT state is shorter than the radiative lifetime (within µs time scale) of Ir(ppy)3.