Stable and efficient white electroluminescent devices based on a single emitting layer of polymer blends

Abstract

An efficient orange-light-emitting polymer (PFTO-BSeD5) has been developed through the incorporation of low-bandgap; benzoselenadiazole (BSeD) moieties into the backbone of a blue-light-emitting polyfluorene copolymer (PFTO poly{[9,9-bis(4-(5-(4-tert-butylphenyl)-[1,3,4]-oxadiazol-2-yl)phenyl)-9',9'-di-n-octyl-[2,2']-bifluoren-7,7'-diyl]-stat-[9,9-bis(4-(NN-di(4-n-butylphenyl)amino)phenyl)-9',9'-di-n-octyl-[2,2']-bifluoren-7,7'-diyl]}) that contains hole-transporting triphenylamine and electron-transporting oxadiazole pendent groups. A polymer light-emitting device based on this copolymer exhibits a strong, bright-orange emission with Commission Internationale de L'Eclairage (CIE) color coordinates (0.45,0.52). The maximum brightness is 13716 cd m(-2) and the maximum luminance efficiency is 5.53 cd A(-1). The use of blends of PFTO-BSeD5 in PFTO leads to efficient and stable white-light-emitting diodes - at a doping concentration of 9 wt%, the device reaches its maximum external quantum efficiency of 1.64% (4.08 cd A(-1)). The emission color remains almost unchanged under different bias conditions: the CIE coordinates are (0.32,0.33) at 11.0 V (2.54 mA cm(-2), 102 cd m(-2)) and (0.31,0.33) at 21.0 V (281 mA cm(-2), 7328 cd m(-2)). These values are very close to the ideal CIE chromaticity coordinates for a pure white color (0.33,0.33).