In one aspect of the invention, an organic light emitting diode device has a substrate, a cathode formed on the substrate, an anode spaced-apart from the cathode, a plurality of electroluminescent units stacked between the cathode and the anode, and a plurality of charge generation layers, each of which is formed between two adjacent electroluminescent units. Each electroluminescent unit has an electron-transport layer, an emission layer formed on the electron-transport layer, and a hole-transport layer formed on the emission layer. The electron-transport layer of the first electroluminescent unit is formed on the cathode, defining a first energy barrier, and the anode is formed on the hole-transport layer of the last electroluminescent unit, defining a second energy barrier. The first energy barrier is higher than the second energy barrier. The first electroluminescent unit has a lifetime longer than that of each of the rest electroluminescent units.