Thermal conversion process of PPV precursor, insertion of poly(N-vinyl carbazole) PVK layer under PPV and doping of PPV upper surface with lithium salt before metal electrode formation were studied. With decreasing thermal conversion temperature of PPV, increase of EL intensity, decrease of threshold voltage and blue shift of EL spectra were observed. The insertion of hole transport/electron blocking PVK layer under PPV increased the maximum applicable voltage to the EL device.