Influence of material impurities in the hole-blocking layer on the lifetime of organic light-emitting diodes

We evaluated the influence of impurities in an organic material used for the fabrication of organic light-emitting diodes (OLEDs) on the lifetime of the fabricated devices. Despite no differences in the current-density-voltage characteristics and external quantum efficiencies of the devices, the lifetime was approximately nine times longer for devices with high-purity 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T), which was used as a hole-block layer. Chlorine-containing impurities derived from T2T had the greatest influence on the lifetime of the OLEDs even though the amount of halogen in the source material was at most 0.9 ppm. On the other hand, the lifetime was not greatly influenced by other impurities even with concentrations up to 0.2%. Therefore, the purities of materials other than the emitter must also be closely controlled.