Covalently linked benzothiadiazole-fullerene adducts for organic optoelectronic devices: synthesis and characterization

Divambal Appavoo; Komal Bhardwaj; Samarendra P Singh; Emmanuel N Koukaras; Rachana Kumar; Bimlesh Lochab

doi:10.1039/d2ra06175a

Covalently linked benzothiadiazole-fullerene adducts for organic optoelectronic devices: synthesis and characterization

RSC Adv. 2022 Dec 15;12(55):35977-35988. doi: 10.1039/d2ra06175a. eCollection 2022 Dec 12.

Authors

Divambal Appavoo^{1

2}, Komal Bhardwaj^{3

4}, Samarendra P Singh⁵, Emmanuel N Koukaras⁶, Rachana Kumar^{3

4}, Bimlesh Lochab¹

Affiliations

¹ Materials Chemistry Laboratory, Department of Chemistry, Shiv Nadar Institute of Eminence Delhi-NCR, Gautam Buddha Nagar Uttar Pradesh 201314 India bimlesh.lochab@snu.edu.in.
² Department of Chemistry, University of Central Florida Orlando FL 32816 USA.
³ Photovoltaic Metrology Group, Advanced Materials and Devices Metrology Division, CSIR-National Physical Laboratory Dr. K. S. Krishnan Marg New Delhi India-110012.
⁴ Academy of Scientific and Innovative Research (AcSIR) Ghaziabad-201002 Uttar Pradesh India.
⁵ Semiconductor Physics Laboratory, Department of Physics, School of Natural Sciences, Shiv Nadar Institute of Eminence India.
⁶ Laboratory of Quantum and Computational Chemistry, Department of Chemistry, Aristotle University of Thessaloniki GR-54124 Thessaloniki Greece.

Abstract

Fullerene adducts have attracted attention in a variety of applications including organic optoelectronic devices. In this regard, we have designed a covalently linked donor-acceptor dyad comprising a fluorobenzothiadiazole-thiophene (BTF₂-Th) unit with the electron acceptor fullerene in an Acceptor-Donor-Acceptor (A-D-A) molecular arrangement. We synthesized and characterized two new covalently bonded benzothiadiazole-based fullerene molecules, mono-adduct, 7 (benzothiadiazole : PC₆₁BM = 1 : 1, anchored terminally via esterification reaction) and multi-adduct, 10-I (benzothiadiazole : PC₆₁BM = n : 1, where n ≥ 1, attached directly to the fullerene core via the Prato reaction) using different synthetic strategies. A broadening of the UV-visible spectra of the modified fullerene derivative with strong absorption from 350 to 500 nm and at low wavelengths is observed as compared to PC₆₁BM. A suitable bandgap, good electronic conductivity, and appreciable solubility in solvents suggest their utility in optoelectronic devices. The mono-adduct 7 showed two-order higher electron mobility as compared to bis-adduct 10-I due to retention of extended conjugation in fullerene, as in the case of PC₆₁BM. Experimentally determined optical properties and energy levels of the fullerene adducts were found to be in good agreement and supported by theoretical calculations. The presence of BTF₂ affects the ground state dipole moments as well as the absorption strengths, most noticeable in the case of two attached BTF₂ moieties. The HOMO and LUMO levels are found to be localized on the fullerene cage with the extension of the HOMO to the BTF₂ unit more and the same is noticed in ground state dipole moment in the side-chain functionalized structure. Such structural arrangement provides easy charge transfer between acceptor and donor units to allow a concomitant effect of favorable optoelectronic properties, energy levels of the frontier orbitals, effective exciton dissociation, and charge transport which may reduce processing complexity to advance single material-based future optoelectronic devices.