White-light-emitting diodes from single polymer systems based on polyfluorene copolymers end-capped with a dye

New polymer white-light-emitting diodes from single polymer systems have been developed. The polymer systems were based on poly(fluorene-co-benzothiadiazole) backbones end-capped with a green-emission dye, N-phenyl-1,8-naphthalimide. By changing the molar ratio of these three units, the electroluminescence (EL) spectra can be adjusted to white-light emission with a structure of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)/emission layer/Ca/Ag. The highest brightness in such a device configuration is 251 cd/m2 at a current density of 400 A/m2 with Commission Internationale de l'Eclairage (CIE) coordinates of (0.31,0.39). The EL spectra show color stability over different operating voltages.