Modifying organic/metal interface via solvent treatment to improve electron injection in organic light emitting diodes

By simply spin-coating the solvents, such as ethanol and methanol, on top of the organic active layer, the performance of polymer organic light-emitting diodes is significantly enhanced. The quantum efficiency is increased by as large as 58% for low work function Ba/Al cathode devices after solvent treatment. An interface dipole between the organic layer and the metal layer induced by the solvent, either from the intrinsic dipole or the interaction between the solvent and the cathode metal, is responsible for the device performance improvement. The interface dipole layer, which is confirmed by the Kelvin Probe Force Microscopy and the photovoltaic measurements, lifts the vacuum level on the metal side, thereby reducing the electron injection barrier at the organic/metal interface, and leading to better device performance.

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► Treating the organic/metal surface with ethanol enhanced the quantum efficiency of OLED by 58%.
► KPFM and photovoltaic measurements verified the existence of an interface dipole layer induced by the solvents.
► The interface dipole reduced the electron injection barrier leading to better device performance.
► The solvent was difficult to remove under the most common solvent removal processes.