An organic light-emitting diode based on heterojunction consists of hole-type polymer PDDOPV [poly (2,5-bis (dodecyloxy)-phenylenevinylene)] and electron-type PPQ [poly (phenyl quinoxaline)] is successfully fabricated. The highest brightness of the heterojunction device is 106 times of the lowest brightness of its own, 365 times of that of single layer device of PDDOPV. The highest luminescent efficiency is 336 times of that of single layer device of PDDOPV. The heterojunction devices can be operated at forward bias voltage, reverse bias voltage and ac (alternating current) voltage. Emission at forward bias voltage and ac voltage are from PDDOPV, but emission at reverse bias voltage includes not only emission from PDDOPV but also emission from PPQ. The reason of the capability of heterojunction device can be operated at reverse bias voltage is that enough high electric field leads to the tilt of energy band, then the tilt of energy band makes the injection barrier thin enough to be injected by carriers through tunnel.