Fullerene-multiwalled carbon nanotube complexes for bulk heterojunction photovoltaic cells

We demonstrate the implementation of multiwalled carbon nanotubes-fullerene (MWNT- C₆₀) complexes in bulk heterojunction organic photovoltaic (OPV) cells. Such a design takes advantage of the C60 as an electron acceptor, while the MWNTs serve as efficient charge transporters. Two types of chemically functionalized MWNTs were used to synthesize these complexes. The first used carboxylated nanotubes (c-MWNT), while the latter were functionalized with octadecylamine (o-MWNT). All the photovoltaic parameters were found to be superior with c-MWNT, and their combined effect led to eight times higher power conversion efficiency. The enhancement was attributed to the electron withdrawing nature of the short carboxylic group which facilitated fast electron transfer from the C60 to the nanotube backbone, whereas the long alky chain on the o-MWNT served as an electron blocker. Therefore, it is evident that the form of functionalization is expected to have significant effect on the performance of OPVs containing carbon nanotubes.