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
Abstract
Oxygen (O2) plasma treatment is one of the most widely applied methods for modifying the electrode work function. However, owing to the instability of O2-plasma treatment effects under air-exposed conditions, it is necessary to confirm whether the O2-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/O2-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 O2-plasma treatment effects at organic semiconductor/electrode interfaces. In addition, we confirmed the preservation of controlled energy-level structures at C60/Au interfaces by examining the relative rates of electron transfer at the C60/Au interfaces, obtained from photoluminescence (PL) measurements.