Enhanced performance of white polymer light-emitting diodes using polymer blends as hole-transporting layers

White polymer light-emitting diodes (WPLEDs) with the Commission Internationale de l'Enclairage coordinates of (0.32, 0.34) are demonstrated with poly(9,9-dioctylfluorene-2,7-diyl) as host and poly(5-methoxy-2-(2(')-ethyl-hexylthio)-p-phenylenevinylene) as guest. Blends of poly[N,N-'-bis(4-butylphenyl)-N,N-'-bis(phenyl)benzidine] (poly-TPD) and poly(N-vinyl-carbazole) (PVK) are introduced into bilayer devices as hole-transporting layers (HTLs). Because the blends combined the hole-injection and hole-transporting capabilities of poly-TPD with electron-blocking capability of PVK, WPLEDs with the blends as HTLs exhibit enhanced performance in comparison with single-layer device and bilayer devices with pure poly-TPD or pure PVK as HTL. With a 1:1 weight ratio of poly-TPD to PVK in the blend, the WPLED achieves a maximum brightness of similar to 5000 cd/m(2) with a maximum electroluminescent efficiency of 3.15 cd/A. (c) 2006 American Institute of Physics.