Using Resonant Soft X-ray Reflectivity (RSoXR) to Probe Vertical Segregation in Organic Semiconducting Thin Films*

Recent studies have demonstrated the efficacy to blending organic semiconducting polymers and small molecules, such as poly(triarylamine) (PTAA) and 2,8-difluoro-5,11-bis(triethylsilylethynyl) Anthradithiophene (diF-TESADT), in order to facilitate film processing and improve device performance. Segregation of the small molecule to the surface or buried interface(s) can dramatically influence device performance in such systems. In this work, we explore the application of Resonant Soft X-Ray Reflectivity (RSoXR) toward determining vertical composition profiles in polymer/small molecule blend films. The resonance-enhanced soft X-ray contrast facilitates accurate determination of film geometry and layer thicknesses without the need for chemical modification of the blend constituents. We also investigate the feasibility of quantitative layer composition analysis by leveraging Near Edge X-ray Absorption Fine Structure (NEXAFS) data obtained from each of the blend components.