Fluorinated single-walled carbon nanotubes as non-fullerene acceptor in organic photovoltaics
Elena Kobeleva a, Leonid V. Kulik a, Olga A. Gurova b, V. A. Zinovyev c
a Institute of Chemical Kinetics and Combustion, Institutskaya 3, Novosibirsk, Russian Federation
b Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
c Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Science, Novosibirsk, Russia
Proceedings of International Conference on Advanced Light Absorbing Materials for Next Generation Photovoltaics (ABSOGEN)
Online, Spain, 2020 November 17th - 18th
Organizers: Hongxia Wang, Xiaojing Hao and Lydia Wong
Poster, Elena Kobeleva, 024
Publication date: 6th November 2020

Spectroscopic and photovoltaic properties of composites of purified and subsequently fluorinated single-walled carbon nanotubes (F-SWCNT) with conjugated polymer poly(3-hexylthiophene) (P3HT) were tested, with the aim of F-SWCNT use as  non-fullerene acceptor in organic photovoltaics. Adding cyclohexanone into o-dichlorobenzene solution of P3HT and F-SWCNTs significantly affects the composite morphology and promotes P3HT/F-SWCNT nanofilament formation, as evidenced from AFM images of spin-coated composite films. Also, nanofilament formation enhances quenching of P3HT photoluminescence by F-SWCNTs.

Dramatic change of SWCNT electronic structure upon fluorination is also evidenced by UV-vis-NIR optical absorption spectra, from which the bandgap of about 1.0 eV is derived for F-SWCNTs. In addition, cyclic voltammetry (CVA) curves for F-SWCNT show reduction peak at -4.3 eV, in contrast to pristine SWCNT (statistical mixture of metallic and semiconducting nanotubes), for which no peaks in CVA curves are observed. This data points to favorable band alignment for photoinduced charge separation in P3HT/F-SWCNT hetegojunction.

 Overall, the experimental results confirm that fluorination efficiently converts metallic SWCNTs into semiconducting ones, and F-SWCNTs can be used for as an electron acceptor component in OPV devices, in combination with polymer donors. However, the performance of P3HT-based organic photovoltaics (OPV) devices with P3HT/F-SWCNT and pristine P3HT as active layer is comparable.  Presently, the performance of P3HT/F-SWCNT devices is limited by F-SWCNT aggregation into bundles, which decreases P3HT/F-SWCNT interface area. Scanning electron microscopy revealed that F-SWCNT are aggregated in bundles with characteristic diameter about 20 nm. The main direction of improving of F-SWCNT photovoltaic performance is their advanced de-bundling.

The work was supported by RFBR grant № 18-29-19089.

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