Electron injection mechanisms of the luminance efficiency of green organic light-emitting devices (OLEDs) fabricated utilizing a cesium carbonate (Cs 2CO 3)/fullerene (C 60) heterostructure acting as an electron injection layer (EIL) were investigated. Current density–voltage and luminance–voltage measurements showed that the current densities and the luminances of the OLEDs with a Cs 2CO 3 or Cs 2CO 3/C 60 EIL were higher than that of the OLEDs with a Liq EIL. The luminance efficiency of the OLEDs with a Cs 2CO 3 EIL was almost three times higher than that of the OLEDs with a Liq EIL. Because the electron injection efficiency of the Cs 2CO 3 layer in OLEDs was different from that of the C 60 layer, the luminance efficiency of the OLEDs with a double EIL consisting of a Cs 2CO 3 layer and a C 60 layer was smaller than that of the OLEDs with a Cs 2CO 3 EIL. The electron injection mechanisms of OLEDs with a Cs 2CO 3 and C 60 double EIL are described on the basis of the experimental results.