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Issue 40, 2019
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“Twisted” conjugated molecules as donor materials for efficient all-small-molecule organic solar cells processed with tetrahydrofuran

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Abstract

High-performance organic semiconductors that can be processed with environmentally benign solvents are highly desirable for printable optoelectronics. Herein, four acceptor–donor–acceptor conjugated molecules, i.e., DRTT-T, DRTT-R, DRTT-OR and DRTT, with 3-ethylrhodanine as acceptor terminal units and 2,5-bis(4,8-di(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophen-2-yl)thieno[3,2-b]thiophene derivatives as donor units were synthesized. 5-(2-Ethylhexyl)thiophen-2-yl, 2-ethylhexyl and 2-ethylhexyloxy were introduced at the β-positions of the central thieno[3,2-b]thiophene (TT) units in DRTT-T, DRTT-R and DRTT-OR, respectively, and unsubstituted TT was used as the central unit in DRTT. As revealed by density functional theory calculations, DRTT-OR and DRTT adopt an almost planar geometry, while DRTT-T and DRTT-R have “twisted” backbones due to the introduction of bulky substituents on TT units. Differing from DRTT-OR and DRTT which are only well soluble in chlorinated solvents such as chloroform, DRTT-T and DRTT-R also show high solubility in “greener” solvents, including toluene and tetrahydrofuran (THF). Non-fullerene small molecule (NFSM) organic solar cells (OSCs) were fabricated with these molecules as donor materials. The molecules (DRTT-T and DRTT-R) with twisted backbones displayed remarkably higher device performance compared to more planar ones (DRTT-OR and DRTT), attributed to the formation of ordered face-on microstructures with π–π stacking distances of 3.7–3.8 Å and interpenetration networks of donor and acceptor components in the blend films based on DRTT-T and DRTT-R. Most importantly, the power conversion efficiencies (PCEs) of DRTT-T and DRTT-R based devices processed with THF reached 9.37% and 10.45%, respectively. This study demonstrates that “twisting” conjugated backbones is an appropriate strategy to design eco-friendly solvent processable organic semiconductors for high-efficiency OSCs.

Graphical abstract: “Twisted” conjugated molecules as donor materials for efficient all-small-molecule organic solar cells processed with tetrahydrofuran

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Publication details

The article was received on 17 Jul 2019, accepted on 16 Sep 2019 and first published on 18 Sep 2019


Article type: Paper
DOI: 10.1039/C9TA07760J
J. Mater. Chem. A, 2019,7, 23008-23018

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    “Twisted” conjugated molecules as donor materials for efficient all-small-molecule organic solar cells processed with tetrahydrofuran

    X. Cheng, M. Li, Z. Guo, J. Yu, G. Lu, L. Bu, L. Ye, H. Ade, Y. Chen and Y. Geng, J. Mater. Chem. A, 2019, 7, 23008
    DOI: 10.1039/C9TA07760J

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