Probing the persistence of energy-level control effects at organic semiconductor/electrode interfaces based on photoemission spectroscopy combined with Ar gas cluster ion beam sputtering

Oxygen (O-2) plasma treatment is one of the most widely applied methods for modifying the electrode work function. However, owing to the instability of O-2-plasma treatment effects under air-exposed conditions, it is necessary to confirm whether the O-2-plasma treatment effects can be continuously maintained at organic semiconductor/electrode interfaces in realistic devices. In the present study, the electronic structures of organic semiconductor/O-2-plasma treated electrode interfaces were characterized by using in situ deposition and ultraviolet photoemission spectroscopy analysis. The structures of the corresponding samples were re-analyzed after a 1-week-long exposure to air to confirm the energy-level changes. To achieve this, we inceptively designed the studies of the energy level alignments of air-exposed samples based on the photoemission spectroscopy combined with Ar gas cluster ion beam sputtering process. The results of our studies clearly confirm the consistency of O-2-plasma treatment effects at organic semiconductor/electrode interfaces. In addition, we confirmed the preservation of controlled energy-level structures at C-60/Au interfaces by examining the relative rates of electron transfer at the C-60/Au interfaces, obtained from photoluminescence (PL) measurements.