Model-independent X-ray reflectivity fitting for structure analysis of poly(3-hexylthiophene) films

Abstract

The properties of regioregular poly(3-hexylthiophene) (P3HT) thin layers prepared on silica surfaces are investigated by X-ray reflectivity measurements and a model-independent fitting approach. As P3HT is a semicrystalline polymer Bragg peaks, corresponding to the repeating distance of lamella sheets, are evident within the reflectivity curves which are not describable with simple one- or two-layer models within a reflectivity simulation minimizing the accuracy of the data evaluation. In this work a model-independent fitting approach is applied to be able to explain the entire reflectivity curve and to gain information on the internal structure within thin films. The thin layers were spin-coated from various chloroform solutions; solution concentrations (c) from 0.2 to 6.3 g/L resulted in P3HT layers with thicknesses (d) ranging from 3.7 to 64 nm with the layer thickness following a d ∼ c0.84 dependence. The model-independent fitting approach reveals directed lamella order is present within the samples prepared from low concentrated solutions while for higher concentrations disorder within the electron density profile is observed. © 2013 American Chemical Society.