The Impact of UV Photoelectron Spectroscopy on the Field of Organic Optoelectronics-A Retrospective

The field of organic electronics has been of widespread interest for a long time. Over the years, device efficiencies increased steadily due to the development of new materials, as well as an improved understanding of the physical mechanisms governing underlying fundamental processes such as charge transport or charge carrier generation and recombination. Especially the positions of energy levels that are responsible for the charge transport throughout a device are of paramount importance. This generated a high demand for reliably measured values. The most important technique that can directly access these values in a thin film is photoelectron spectroscopy. The very fruitful collaboration between surface scientists and device specialists is reviewed here, showing a range of experiments through which UV photoelectron spectroscopy helped to unravel the working mechanisms of organic semiconductors in devices