Various efforts have been made to increase the efficiency of organic solar cells by using CNTs, having excellent electrical and structural characteristics. One of the main drawbacks of CNT-free organic solar cells is that they absorb light only in a small wavelength range, resulting in low overall power conversion efficiency. Since CNTs vary in their chirality and energy band gaps accordingly, CNTs can be combined with organic solar cells to absorb light in a wider wavelength range. When making devices, if the metallic single-walled carbon nanotubes (m-SWNTs) present in semiconducting single-walled carbon nanotubes (sc-SWNTs)-conductive polymer composite, device will be short circuited due to the m-SWNT. Thus, the process that separates highly pure sc-SWNT from the SWNT mixture before the binding process of the SWNT with the conductive polymer is essential. But this approach requires tedious and laborious experimental steps (i.e. sonication, chemical reaction, centrifugation, post-annealing treatment, etc.) to get pure sc-SWNT.
In this study, we demonstrate that semiconducting polymer with appropriate length of side chain can selectively suspends only sc-SWNT. Under appropriate experimental conditions, polymer selectively combines with sc-SWNT, having similar circumference length with side chain length of polymer. Then, sc-SWNT-polymer composite can be easily separated from m-SWNT using mild centrifugation. We were able to simplify the conventional SWNT separation and semiconducting SWNT-conductive polymer bonding process in one step.
In this study, HipCO SWNT and CoMoCAT SWNT were used as SWNT, Poly (3-dodecylthiophene-2,5-diyl) (P3DDT) and P8TBTz-C12 were used as a conductive polymer, and toluene as a solvent.
Absorption measurement clearly showed that m-SWNT was clearly removed from polymer-sc-SWNT solution obtained from experiment. Using this process, low cost, high performance CNT applied organic solar cell would be expected.