X-ray based tools for the investigation of buried interfaces in organic electronic devices

[Display omitted] ► We fabricated orthogonal soluble polymer stacks and probed the buried interface by X-ray reflectivity. ► Depending on the used solvent of the organic semiconducting material the interface morphology changed significantly. ► Grazing incidence X-ray diffraction exhibits the molecule alignment in the investigated polymer stack. ► The buried interface roughness within the polymer stack was correlated to the OTFT performance containing the stack. X-ray reflectivity combined with grazing incidence diffraction is a valuable tool for investigating organic multilayer structures that can be used in devices. We focus on a bilayer stack consisting of two materials (poly-(3-hexylthiophene)) (P3HT) and poly-(4-styrenesulfonic acid) (PSSA) spin cast from orthogonal solvents (water in the case of PSSA and chloroform or toluene for P3HT). X-ray reflectivity is used to determine the thickness of all layers as well as the roughness of the organic–organic hetero-interface and the P3HT surface. The surface roughness is found to be consistent with the results of atomic force microscopy measurements. For the roughness of P3HT/PSSA interface, we observe a strong dependence on the solvent used for P3HT deposition. The solvent also strongly impacts the texturing of the P3HT crystallites as revealed by grazing incidence diffraction. When applying the various PSSA/P3HT multilayers in organic thin-film transistors, we find an excellent correlation between the determined interface morphology, structure and the device performance.