THIN-FILM HETROJUNCTION BY CARBON NANOTUBE DERIVATIVES WITH ENHANCED SOLUBILITY AND OPTICAL PROPERTIES

Abstract

The combination of single-walled carbon nanotubes (SWNTs), characterized by high electron mobility, with p-type semiconducting polymers could lead to an overall improvement in the exciton dissociation and carrier extraction efficiencies in practical devices.1However, one of the main concern in the use of SWNTs, relates to the their scarce solubility. Chemical modification has been widely employed to increase the solubility of SWNTs, but usual reaction conditions limit such syntheses to a small scale with low productivity. Here, we employ SWNTs which have been functionalized with aromatic and heteroaromatic moieties via 1,3-dipolar cycloaddition and through diazotization reaction under batch and continuous-flow conditions. This offers a safer, scalable processing and the opportunity to a rapid reaction screening using a relatively small amount of reagents.2 Such systems in combination with P3HT have been used to fabricate bulk heterojunctions (BHJ) by Langmuir-Blodgett, which offers a simple method of producing ultrathin-films with fine control over thickness. Thanks to the improved solubility of SWNT derivatives we prepared multi-planar heterojunctions (MHJ) consisting of alternate layers of P3HT and SWCNTs, by horizontal lifting (Langmuir-Schaefer) technique. Then we induced a transition from MHJ to BHJ by thermal annealing to mix the layers. While the degree of functionalization ensured by diazotization, higher than 1,3-dipolar cycloaddition, improves processability, fluorescence quenching measurements have demonstrated that thienyl groups ensure a stronger interaction with P3HT and consequently a better electron transfer. Such properties have been modulated within the thin film by changing its internal morphology tuning the parameters of the mixing process. Thienyl derivatives obtained through controllable functionalization of SWNTs in flow conditions are promising candidates for the incorporation in the active layer of OPV cells.