Single-wall carbon nanotubes (SWCNT) have attracted great interest for applications in a variety of research areas, including electronics and functional materials. However, a good dispersion of these materials in polymer matrices is a demanding factor in order to obtain more homogeneous and less bundled films for constructing optoelectronic and electrochemical devices. In this report we describe a covalent modification with thiophene groups located at the edges and at defects in SWCNT to modify the interaction with the polymer matrix aiming at its application in solar cells. The modified SWCNT and its composites with poly(3-octylthiophene) were characterized by Raman, infrared, UV-vis, and luminescence spectroscopies and cyclic voltammetry. The best bulk heterojunction solar cell was obtained using 5 wt % of the modified carbon nanotube (SWCNT-THIOP) and shows open circuit voltage (VOC), short-circuit current (I sc ), and efficiency (η) of 0.75 V, 9.5 µA cm -2 , 0.184%, respectively.