A study of confinement induced surface structure of P3HT and P3HT/PCBM blend using grazing incidence diffraction

Abstract

Thin films of P3HT and its blend with PCBM were investigated for vertical segregation of the crystalline structure using grazing incidence diffraction. The films were cast from a solution (P3HT/PCBM) on silicon substrates using the spin-coating technique, and their thickness (170–580 Å) were determined using x-ray reflectivity. In the grazing incidence diffraction technique, the scattered intensity is measured below and above the critical angle of incidence to distinguish the surface structure from the structure of the film underneath. We obtained a diffraction peak due to the lamellar alignment of P3HT perpendicular to the substrate. For thick films of pristine P3HT, the surface was more crystalline as compared to that of the entire film. In the blend films, the surface was found to be amorphous with crystalline structure underneath. The substrate interaction strongly influenced the crystal formation upon annealing at 110 °C as the structure of thicker films (∼600 Å) was strongly modified, whereas that of thinner films (170–290 Å) was negligibly affected.