We demonstrate an organic p–n junction as an efficient electron injection layer for green inverted bottom-emission organic light emitting diodes (IBOLEDs). The organic p–n junction composed of a p-CuPc/n-Bphen layer showed very efficient charge generation under a reverse bias reaching to 100 mA/cm2 at 0.3 V, and efficient electron injection from indium tin oxide (ITO) when adopted in IBOLEDs. Moreover, the organic p–n junction resulted in the same current density–voltage–luminance characteristics independent of the work function of the cathode, which is a valuable advantage for flexible displays.