Development of efficient solution-processed red phosphorescent organic light-emitting diodes using carrier transport materials

We report on efficient solution-processed red emissive phosphorescent organic light-emitting diodes (PhOLEDs) employing bis[9-ethyl-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium acetylacetonate (Et-Cvz-PhQ)2Ir(acac) and bis[9-(2-(2-methoxyethoxy)ethyl)-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium acetylacetonate (EO-Cvz-PhQ)2Ir(acac) doped into polymer host PVK, blended with electron transporting material OXD-7, and optimized concentration of carrier-transporting material TPD. The optimized PhOLEDs doped with 16 wt% carrier-transporting material shows a maximum luminance efficiency and power efficiency of 4.66 cd/A and 1.22 lm/W, which were increased by 40% and 20%, respectively, compared with that of reference device. The electroluminescence (EL) spectra exhibited the characteristic spectrum of (Et-Cvz-PhQ)2Ir(acac) and (EO-Cvz-PhQ)2Ir(acac) with its maximum at 630 nm and CIE (Commission International de L’Eclairage) coordinate of (0.66, 0.33).