Synthesis and characterization of light-emitting oligo(p-phenylene-vinylene)s and polymeric derivatives containing three- and five-conjugated phenylene rings. II. Electro-optical properties and optimization of PLED performance

Abstract

A series of multilayer polymeric light-emitting diodes (PLEDs) containing an electron-transporting layer (ETL), that is tris(8-quinolinolato)-aluminum(III) (Alq) and 2,2',2"-(1,3,5-phenylene)-tris[1-phenyl-1H-benzimidazole] (TPBI), were fabricated by doping fluorescent oligo(p-phenylene-vinylene)s (BIII and BV) and polymer derivatives (PBV) into poly(N-vinyl carbazole) (PVK). These PLEDs can be optimized by the design of multilayer device configurations (brightness increased 8-15 times by addition of ETL) and possess greenish electroluminescent (EL) spectra peaked about 500-540 nm. A remarkably high brightness of 56,935 cd/m(2) with a power efficiency of 3.25 lm/W was obtained in the device of PVK:BVOC8-OC8 (100:20)/Alq (60 nm/60 nm). It suggests that the emission mechanism (including the conjugated and excimer emissions of BVOC8-OC8 emitters) originates from both of BVOC8-OC8 and ETL (Alq and TPBI) by varying the concentration of chromophores and adjusting the thickness of ETL. The concentration effect of the emitters in PVK (i.e. PVK:BVOC8-OC8 = 100:5, 100:20, and 100:100 wt %) and the influence of the ETL (including its thickness) on the EL characteristics are also reported. (c) 2006 Wiley Periodicals, Inc.