Soft X-ray characterisation of organic semiconductor films

Organic semiconductor devices such as organic solar cells and organic field-effect transistors are based on blended and/or multilayered structures. Many organic semiconductors used in high-performance devices are also semicrystalline or liquid crystalline with a complex relationship between film microstructure and device performance. Unravelling structure-function relationships in organic semiconductor devices therefore requires structural probes that have high chemical specificity, sensitivity to molecular orientation and order and high spatial resolution. Soft X-rays have proven to be versatile in spectroscopy, microspectroscopy and scattering experiments providing contrast derived from differences in the near-edge X-ray absorption spectra of different organic semiconductors. Furthermore, the sensitivity of polarised soft X-ray beams to the orientation of bonds in organic materials makes them a unique probe of molecular orientation. This feature article provides an overview of the range of microscopy, reflectivity and scattering techniques based on soft X-rays that have been developed in recent years and their utility for providing new insight into the complex structure of organic semiconductor thin films.