Effect of halohydrocarbon solvents on the dielectric performance of a polymer film and its application to inorganic electroluminescent devices

Polymer films with halohydrocarbon solvents as additive solvents were fabricated to investigate the solvent effect on dielectric performance. Bromobenzene, chlorobenzene (CB), chloroform, and fluorobenzene (FB) were used as halohydrocarbon solvents. The cyanoethyl pullulan (CRS) polymer film with CB had a dielectric constant of 21.5 with a dielectric loss of 0.017 at 100 Hz, which exhibited a 37% increase in dielectric constant compared to the neat CRS polymer film. Increment of the dielectric constant is attributed to the high polarizability of carbon-chlorine bonds originated from CB absorbed in CRS. For the case of the CRS polymer film with FB, the dielectric constant did not increase due to the low polarizability of carbon-fluorine bonds. In order to verify the dielectric performance of the CRS polymer film with CB (CRS/CB), AC-driven inorganic powder electroluminescent (EL) device was fabricated using the green emission ZnS:Cu,Cl phosphor particles. An EL device with CRS/CB polymer film as a dielectric layer exhibited a 37% and 55% increase in luminance and efficiency, respectively compared to that with neat CRS polymer. This increase in EL performance was attributed to the increase of charge carrier density at the interface between the emitting and dielectric layers, resulting in the increased possibility of the charge carrier tunneling into phosphor particles.