Efficient white-light-emitting diodes based on polymer codoped with two phosphorescent dyes

Abstract

Efficient white-light-emitting diodes (WPLEDs) based on a polymer codoped with two phosphorescent dyes were fabricated by the spin-casting method. Polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) (PFO-poss) was used as the host and blue light emitter. Phosphorescent emitters, fac-tris[2-(4′-ter-butyl)phenylpyridine] iridium (III) [Ir(Bu-ppy)3] and bis-(1-phenylisoquinolyl)iridium(III)(1-trifluoro) acetylacetonate [(Piq)2Ir(acaF)] with green and red emission, respectively, were used as the guests. The electroluminescence spectrum can be tuned by changing concentration of the guests. The structure of the WPLEDs is indium tin oxide (ITO)/poly(ethlenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)/ PVK/PFO-poss codoped with Ir(Bu-ppy)3 and (Piq)2Ir(acaF)∕Ba∕Al. The PVK layer [poly(N-vinylcarbazole)] acts as the function of blocking electron penetrating from PFO-poss to PEDOT. When the doping concentrations are 0.14 wt % for both Ir(Bu-ppy)3 and (Piq)2Ir(acaF), the efficient white-light emission with CIE coordinates of around (0.33, 0.33) is achieved. The current efficiency reaches 5.5lm∕W (9cd∕A), and the maximum luminance of 10200cd∕m2 was gained at 11 V. The mechanisms of the WPLEDs with high efficiency are discussed.