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.PSSiW3/CsF/Al (ITO: indium tin oxide; PEDOT.PSS: poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene)) exhibit a low turn-on voltage of 2.8 V and a luminance of ca. 10(3) 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'Eclairage (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 cm(-2), with an almost constant color render index (CRI) value of 82 at all measured current densities.