Efficient white-electrophosphorescent devices based on a single polyfluorene copolymer

Abstract

An efficient white-light-emitting polymer (W3) is realized by covalently attaching a green fluorophore and a red phosphor into the backbone and the side chains, respectively, of polyfluorene at a concentration of 0.04 mol %. In addition, charge-transporting pendant units are included to improve carrier injection and transport. White-electrophosphorescent devices with the structure ITO/PEDOT.PSS/W3/CsF/Al (ITO: indium tin oxide; PEDOT:PSS: poly(styrenesulfonate)-doped poly(3,4-ethylene-dioxythiophene)) exhibit a low turn-on voltage of 2.8 V and a luminance of ca. 103 cd m-2 at below 6 V. The peak luminance and power-conversion efficiencies are 8.2 cd A-1 and 7.2 lm W-1 respectively. Furthermore, the device shows relatively stable white emission: the Commission Internationale d'Éclairage (CIE) chromaticity coordinates of the devices change only slightly from (0.35,0.38) at 10 mA cm-2 to (0.33,0.36) at 100 mA cm2, with an almost constant color render index (CRI) value of 82 at all measured current densities. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.