The effects of heat-treatment and a small amount of lithium perchlorate (LiClO4) doping on the electrical and luminescence properties of poly (N-vinylcarbazole) film mixed with electron transporting material (Bu-PBD or Alq(3)) and Coumarin6 were investigated. It was found that the efficiencies of the light emitting diode with and without LiClO4 were improved by heat-treatment in the vacuum. It was also found that the current flow and luminance were enhanced by doping a small amount of LiClO4. The efficiency of the film with LiClO4 was improved by the prebiasing with an electric field of 1.5-2.0 MV/cm, and it was ascribed to the ionic charge polarization at the electrode/film interface.