Efficient White‐Electrophosphorescent Devices Based on a Single Polyfluorene Copolymer

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‐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'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 cm –2 , with an almost constant color render index (CRI) value of 82 at all measured current densities.