Self-organized structures of $\pi $-conjugated polymer chains at the solid-polymer interface

The interfacial structure of poly(3-hexylthiophene) (P3HT) conjugated polymer on planar solid substrates was investigated by a combination of surface sensitive experimental techniques. 50 nm-thick spin-cast P3HT films were prepared on hydrogen fluoride etched Si substrates and then annealed at 170 $^{\circ}$ C for up to 100 h under vacuum. The films were then solvent-leached with chloroform repeatedly until the thickness of the residual layer remained unchanged. The X-ray reflectivity and atomic force microscopy experiments elucidated the formation of homogenous 3.5 nm-thick adsorbed P3HT layer on the Si substrate. Grazing incidence X-ray diffraction (GIXD) illuminated that the $\pi $-conjugated polymer chains in the absorbed layer still predominantly self-assembled into ``edge-on'' orientated lamella at the interface despite the reduced degree of the lamellar ordering compared with that of the original 50 nm-thick P3HT thin film. In addition, the interfacial structure of a P3HT:[6,6]-phenyl C$_{\mathrm{61}}$-butyric acid methyl ester (PCBM) blend film was studied by the same experimental strategy, and the details will be also discussed in the presentation.