The performance of bulk heterojunction organic solar cells based on poly(3-hexylthiophene) and PCBM can be enhanced by the employment of suitably tailored partially substituted poly(oligothiophene)s. In view of this, three new polythiophenes with a different content in a hexamethylenic side chain ending with a methoxy group have been prepared and characterized completely using NMR and FT-IR techniques. The optical features of the synthesized polymers have been compared by registering their UV-Vis spectra both in different solvent-non solvent systems and in film, and their thermal stability, electrical conductivities, and photovoltaic properties have been carefully analyzed. In particular, the two samples with low side-chain content showed very promising electrical performances even if their use as the active layer in polymer-based organic photovoltaic (OPV) solar cells has not yet been fully optimized. (C) 2011 Elsevier Ltd. All rights reserved.