Abstract 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 ...