A well-defined diblock copolythiophene, poly(3-hexylthiophene)-b-poly(3-(2-(2-(2-methoxyethoxy) ethoxy)ethoxy)methylthiophene) (P3HT-b-P3TEGT) was successfully synthesized by a Grignard metathesis (GRIM) polymerization. The structure of the block copolymer was confirmed by size exclusion chromatography (SEC), (1)H NMR spectroscopy, differential scanning calorimetry (DSC), ultraviolet-visible (UV-vis) spectroscopy and fluorescence spectroscopy. The self-assembled structure of the block copolythiophene was investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and synchrotron grazing incidence X-ray scattering (GIXS). These analyses found that the block components in films form vertically oriented lamellar structure via phase separation. Furthermore, both the phases were found to consist of molecular multi-layers respectively, in which the layers stack in the out-of-plane of the film. The P3HT phase exhibited crystalline, which is originated from the pi-pi stacked thiophene backbones. In contrast, the poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3TEGT) phase revealed amorphous. Overall, the amphiphilic nature of P3HT-b-P3TEGT successfully demonstrated to lead to well-defined self-assembly structure in films. (C) 2011 Elsevier Ltd. All rights reserved.