Control of emission outcoupling in liquid-crystalline fluorescent polymer films

We report the improvement of light outcoupling efficiency of thermally annealed thin liquid crystalline light-emitting polymer films. Unlike the generally observed phenomena from thermally annealed fluorescent polymer films, in the liquid-crystalline fluorescent polymer (LCFP) films, the transverse electric waveguide mode was suppressed due to the light scattering by liquid-crystalline domains in the film. In addition, the optical anisotropy of the annealed LCFP was increased. As a result, the light extraction of photoluminescence and electroluminescence emission in the annealed LCFPs was enhanced by ∼2 times because the emitted light loss by waveguide was minimized. This approach to improve light extraction by forming scattering domains inside the LCFP film gives an insight to improve the outcoupling efficiency of the EL devices in the viewpoint of the material design and film morphologies without employing external geometric device structures.