A chlorinated barium titanate-filled polymer composite with a high dielectric constant and its application to electroluminescent devices

We have studied the effect of chlorination on the dielectric performance of a barium titanate (BTO)–polymer film. Functionalization of BTO powder particles with chlorine (Cl) atoms and/or Cl-containing functional groups was achieved by a simple treatment using chlorinated solvents. The chlorinated BTO (Cl-BTO) particles were incorporated into a cyanoethyl-based polymer and the mixture was spin-coated to produce a composite film. The dielectric constant of the composite film with Cl-BTO was as high as 208 at a frequency of 10 Hz, showing a 2.5-fold increase in dielectric constant compared to composites composed of the neat BTO and the cyanoethyl-based polymer at a frequency of 10 Hz. The observed dramatic increase in dielectric constant would be caused by the interfacial polarization due to the p-type doping effect resulting from the presence of strong electronegative Cl atoms. Given a relatively high dielectric constant, composite films with Cl-BTO were further exploited as a dielectric layer in an inorganic electroluminescence (EL) device. The luminance of the EL device with Cl-BTO was 4090 cd m−2 at a frequency of 1 kHz, showing a 2.03-fold increase in luminance compared to that with the untreated BTO. The improved performance of the EL device is attributed to a high dielectric constant of the composite films that allow for efficient charge carrier tunneling into the phosphor and therefore enhanced luminance and efficiency.