In modern electronics, it is essential to create almost arbitrary band structures by adjusting the energy bands and the band gap. Until now, band structure engineering in organic semiconductors has not been possible, since they usually exhibit localized electronic states instead of energy bands. In a recent publication , we showed that it is possible to continuously shift the ionization energy (IE) of organic semiconductors over a wide range by mixing them with halogenated derivatives. This tuning mechanism is based on interactions of excess charges with the mean quadrupole field in the thin film.
In this work, we raise the question whether the band structure engineering concept can be generalized to other organic semiconductor materials and even be used to tune the size of the band gap. As a model system we study oligothiophenes and in particular we address questions not only about the energy landscape, but also about the micro-structure and the molecular mixing in the film. For this purpose, we analyze optical measurements as well as photoelectron spectroscopy measurements of single and blended layers.
 M. Schwarze et al., Science 352, 1446 (2016)