A facile, covalent modification of single-wall carbon nanotubes by thiophene for use in organic photovoltaic cells

Thiophene was nitrated to afford 2-nitrothiophene. The hydrogenation of the latter gave 2-aminothiophene that was used for amidation of single-wall carbon nanotubes functionalized with carboxylic acid groups (SWCNT-COOH). The modified carbon nanotubes (SWCNT-CONHTh) were fully characterized by FT-IR, H-1 NMR, UV-vis absorption, photoluminescence (PL) emission, Raman spectroscopy, X-ray, and TGA. The properties of the modified nanotubes were compared with those of the pristine SWCNT, indicating that the thiophenes were covalently attached to the SWCNTs via amide linkages. The modified SWCNT showed enhanced solubility, and thus better dispersion in common organic solvents. Furthermore, the SWCNT-CONHTh Was used as dopant in polymer-fullerene photovoltaic cells. The power conversion efficiency (1.78%) of the polymer-fullerene cell with the SWCNT-CONHTh was superior to both the pristine cell without nanotubes (1.00%) and the cell with the unmodified SWCNTs (1.41%). The device takes advantage of the electron accepting feature of fullerenes and the high electron transport capability of the SWCNTs. The enhancement of the photovoltaic response with the use of the SWCNTs modified by thiophene compared with the as-prepared SWCNTs is believed to be due to more efficient dispersion of the modified SWCNTs resulting in a more homogenous photoactive layer. (C) 2009 Elsevier B.V. All rights reserved.