In this paper, the single and double heterostructure organic light-emitting devices(OLEDs) were fabricated. The single heterostructure OLED(TYPE 1) is consisted of TPD as a HTL(hole transfer layer) and Alq$_3$as an EML(emitting layer). The double heterostructure OLED(TYPE 2) is consisted of TPD as a HTL, Alq$_3$as an EML and PBD as an ETL(electron transfer layer). The another double heterostructure OLED(TYPE 3) is consisted of TPD as a HTL, PBD as an EML and Alq$_3$as an ETL. We obtained a strong green emission device with maximum EL emission wavelength 500nm in TYPE 3. When the applied voltage was 12V, the emission luminescence was 120.9cd/㎡. The chromaticity index of TYPE 3 was x=0.29, y=0.50. In the characteristic plot of current-voltage, TYPE 3 device was turned on at 6.9V. This voltage was a fairly low turn-on voltage. TYPE 1 and 2 device were turned on at 10V and 8.9V respectively. These types showed no good properties over that of TYPE 3.