We present the first evidence of charge injection improvement in an organic electroluminescent device provided by a single ionic molecular layer. A hole-dominated, hybrid organic-inorganic light-emitting device is used as a probe to verify the effectiveness of the ionic compound monolayer on modifying the metal oxide cathode. The rearrangement of ions under an applied bias induces a strong field at the electrode-organic interface resulting in an enhancement of the electron injection into the organic semiconductor. A strong decrease in turn-on voltage for electroluminescence is observed for the device containing the ionic molecular monolayer.