Thiophene-benzothiadiazole-thiophene (D-A-D) based polymers : Effect of donor/acceptor moieties adjacent to D-A-D segment on photophysical and photovoltaic properties

Sonar, Prashant, Williams, Evan L., Singh, Samarendra P., & Dodabalapur, Ananth (2011) Thiophene-benzothiadiazole-thiophene (D-A-D) based polymers : Effect of donor/acceptor moieties adjacent to D-A-D segment on photophysical and photovoltaic properties. Journal of Materials Chemistry, 21(28), pp. 10532-10541.

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Abstract

New push-pull copolymers based on thiophene (donor) and benzothiadiazole (acceptor) units, poly[4,7-bis(3-dodecylthiophene-2-yl) benzothiadiazole-co- thiophene] (PT3B1) and poly[4,7-bis(3-dodecylthiophene-2-yl) benzothiadiazole-co-benzothiadiazole] (PT2B2), are designed and synthesized via Stille and Suzuki coupling routes respectively. Gel permeation chromatography shows the number average molecular weights are 31100 and 8400 g mol-1 for the two polymers, respectively. Both polymers have shown absorption throughout a wide range of the UV-vis region, from 300 to 650 nm. A significant red shift of the absorption edge is observed in thin films compared to solution of the copolymers; the optical band gap is in the range of 1.7 to 1.8 eV. Cyclic voltammetry indicates reversible oxidation and reduction processes with HOMO energy levels calculated to be in the range of 5.2 to 5.4 eV. Upon testing both materials for organic field-effect transistors (OFETs), PT3B1 showed a hole mobility of 6.1 × 10-4 cm2 V-1 s -1, while PT2B2 did not show any field effect transport. Both copolymers displayed a photovoltaic response when combined with a methanofullerene as an electron acceptor. The best performance was achieved when the copolymer PT3B1 was blended with [70]PCBM in a 1:4 ratio, exhibiting a short-circuit current of 7.27 mA cm-2, an open circuit voltage of 0.85 V, and a fill factor of 41% yielding a power conversion efficiency of 2.54% under simulated air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm-2). Similar devices utilizing PT2B2 in place of PT3B1 demonstrated reduced performance with a short-circuit current of 4.8 mA cm -2, an open circuit voltage of 0.73 V, and a fill factor of 30% resulting in a power conversion efficiency of roughly 1.06%.

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27 citations in Web of Science®
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ID Code: 75257
Item Type: Journal Article
Refereed: Yes
Keywords: Absorption edges, Air mass, Benzothiadiazoles, Electron acceptor, Field effect transport, Fill factor, HOMO energy levels, Illumination conditions, Methanofullerenes, Number average molecular weight, Photophysical, Photovoltaic property, Photovoltaic response, Power conversion efficiencies, Red shift, Reversible oxidation, Suzuki couplings, Absorption, Conversion efficiency, Copolymerization, Copolymers, Cyclic voltammetry, Gel permeation chromatography, Hole mobility, Materials testing, Open circuit voltage, Organic field effect transistors, Polymers, Size exclusion chromatography, Thiophene, Photovoltaic effects
DOI: 10.1039/c1jm10649j
ISSN: 0959-9428
Divisions: Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2011 The Royal Society of Chemistry.
Deposited On: 02 Oct 2014 22:42
Last Modified: 22 Jun 2017 09:01

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