Effect of methanol treatment on performance of phosphorescent dye doped polymer light-emitting diodes

Methanol treatment was performed on the emissive layer (EML) of conjugated polymer hosted phosphorescent dye doped polymer light-emitting diode (PLED) with a device configuration of indium tin oxide (ITO)/poly(ethylene dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)/poly(N-vinylcarbazole) (PVK)/poly(9,9-dioctylfluorene) (PFO):30 wt% 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD):2 wt% fac-tris(2-phenylpyridine) iridium (III) (Ir(ppy)3)/Ba/Al. Improvement of the external quantum efficiency and luminous efficiency were observed. After methanol treatment, partial electron-transportant dopant PBD was selectively removed from the EML. Though PBD was doped in the EML to achieve more balanced charge transport, its partially removal resulted in further enhancement of PLED performances. The surface topography of EML shows the reduction of PBD aggregation which is detrimental to luminescence.