Fabrication and Characteristics of Increased Efficiency of Layered Polymeric Electroluminescent Diodes

We fabricated polymer electrophosphorescent organic light-emitting diodes (PHOLEDs) with a layered structure using water-soluble materials and a poly(n-vinylcarbazole) (PVCz) host doped with fac -tris(2-phenylpyridyl)Ir(III) (Ir(ppy) 3 ). The 3-layered structure of PHOLEDs exhibit emission from Ir(ppy) 3 (the emission maximum was observed at 520 nm) and show a significantly improved current efficiency of 21.0 cd/A and a luminous power efficiency of 5.2 lm/W (peak external quantum efficiency of about 6.0% has been realized compared to the conventional PHOLEDs with 2-layered structure. Furthermore, the 4-layered structure of PHOLEDs using tris(8-hydroxyquinoline)aluminum (Alq 3 ) as electron transport layers exhibited a current efficiency of 28.1 cd/A and a luminous power efficiency of 6.0 lm/W (peak external quantum efficiency of about 8.0%). Our results suggest that the layered structure using water-soluble materials improves device performances and is effective for facilitating the fabrication by a wet process.