Organic light emitting diodes (OLED) employing an Ir complex with coumarin (C6) and acetylacetone (acac) ligands Ir(C6)2(acac) are studied. This novel Ir complex can be used both as electron transporting material and light emitting dopant. From a calculation, the PL quantum efficiency of Ir(C6)2(acac) in dilute chloroform solution is 70%. With a device structure of ITO (indium tin oxide)/T-NATA(4,4’,4"-tris(N-(2-Naphthyl)-N-phenyl-amino)triphenylamine)(40nm)/NPB(N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’diamine)(40nm)/Alq3(tris-(8-hydroxy-quinoline)aluminum):Ir(C6)2(acac)(1%)(40nm)/Alq3(tris-(8-hydroxy-quinoline)aluminum)(40nm)/LiF(Lithium fluoride)(1nm)/Al
(120nm), a green color (CIE coordinates x=0.22; y=0.65) and a max luminance of 33792 cd/m2 and an efficiency of 12cd/A are obtained. The solid film of Ir(C6)2(acac) excited at 400 nm shows a strong orange PL emission with a peak at 562 nm. This means When C6 is coordinated with Ir metal; the concentration quench is significantly prevented. As a result, even J is high to 200mA/cm2, the device with a structure of ITO/T-NATA/NPB/Alq3:Ir (C6)2(acac)(1%)/Alq3 (40nm)/ LiF/Al can maintain the high efficiency (11.9cd/A) and the high luminance (23683 cd/m2).
A 102X64 monochromatic passive matrix organic light-emitting diode (PMOLED) display was studied for its decay process. The structure of the device was ITO(indium tin oxide )/CuPc (copper phthalocyanine/NPB(N,N'-di(naphthalene-l-yl)-N,N'-diphenyl-benzidine)/Alq3(tris-(8hydroxyqu-inoline)aluminum):C545(coumarin)/Alq3/LiF/Al. We carried out a vision inspection and electrical (I-V) and optical characterizations, analyzed the EL (electroluminescence) and PL (photoluminescence) spectra before and after the aging test. The aged device under constant current appeared higher driving voltage, smaller leak current, lower EL and PL intensities which were come from the peeling of cathode/organic layers, the burning of shorted routes between the electrodes and the decomposition of light-emitting materials. The EL intensity remains 75.6% while the PL does 81.4% of their initials values after 17 hours aging, which means the EL and PL decay simultaneously, i.e. the decomposition of emissive material is dominant in the decay process and results in the permanent damage in the display panel.