Vertical Conducting Nanodomains Self-Assembled from Poly(3-hexyl thiophene)-Based Diblock Copolymer Thin Films

We have synthesized pi-conjugated poly(3-hexyl thiophene)-block-poly(methyl methacrylate) (P3HT-b-PMMA) with a P3HT molecular weight of 11 kDa and a PMMA volume fraction of 0.53, which potentially has several organic electronic applications. Its phase-separation behavior was investigated for various thicknesses cast from organic solvents. When cast onto 300 nm thick SiO2 dielectrics from toluene, in which the P3Ht segments have limited solubility, the P3HT-b-PMMA films consist of nanofibrillar self-assemblies of laterally pi-stacked P3HT chains. In contrast, the P3HT segments were found to be highly mobile in chlorobenzene, generating a typical phase-separation morphology consisting of vertically conducting P3HT nanodomains of these dielectrics. As the thickness of the cast films increased, hoever, the topmost surface becomes covered with pi-conjugated nanofibrils that are laterally oriented with respect to the surface. Due to the anisotropic domain orientations of P3HT, top-gate organic field-effect transistors (OFETs) containing the P3HT-b-PMMA films exhibited enhanced electrical performance compared to bottom-gate OFETs.