Efficient green-phosphorescent light-emitting diodes based on polymeric binary-host systems

The fabrication of the green polymer light-emitting diodes based on emission from the phosphorescent molecule fac tris(2-phenylpyridine) iridium doped into a polymeric binary-host is reported. The main host used in the PLEDs was a non-conjugated polymer, poly(9-vinyl carbazole) (PVK). To realize the balanced transport of the holes and the electrons, a conjugated polymer, poly(9,9-dioctylfluorene) (PFO) was used as the assisting host. According to the experimental results, we found that the PLEDs can achieve the balance in charge transport and the recombination zone is still confined in the emissive layer by controlling the ratio of PVK to PFO. The luminous efficiency is enhanced by >40% while the external quantum efficiency can be increased by >38% in a polymeric binary-host system as compared to those of traditional device configuration, which is attributed to the balanced transport of the charged carrier.