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Issue 19, 2017
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Naphthalene substituents bonded via the β-position: an extended conjugated moiety can achieve a decent trade-off between optical band gap and open circuit voltage in symmetry-breaking benzodithiophene-based polymer solar cells

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Abstract

Bare naphthalene units bonded via the α- and β-positions as side chain substituents on an asymmetric benzodithiophene (BDT) building block were employed in the design of new light-harvesting polymers for the first time. Accordingly, two D–A type polymers, based on naphthyl-substituted BDT as a D-building block and the well-known 4,7-di(thiophen-2-ethylhexyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) as an acceptor unit, were synthesized. The polymer PBDTβNPFBT with naphthalene bonded via the β-position exhibits an appropriate π–π distance. The naphthalene rings efficiently broaden the absorption and narrow the optical band gap (Eoptg), by extending the degree of π-conjugation, which is beneficial for capturing more photons and thus improving the short-circuit current density (JSC). Meanwhile, PBDTβNPFBT-based devices also exhibit a desirable high open circuit voltage (VOC), due to the low saturation dark current density (JS) arising from the exactly appropriate π–π distance. As a result, the power conversion efficiency (PCE) of 9.80% for the PBDTβNPFBT/PC71BM-based PSC is the highest efficiency ever obtained among the reported BDT and DTBT backbone photovoltaic polymers. In addition, a PCE of 7.33% was obtained for PBDTβNPFBT/ITIC without any treatment, which is also impressive for non-fullerene PSCs. Thus, it can be concluded that a naphthyl unit bonded via the β-position can lead to a better trade-off between Eoptg and VOC, ultimately increasing the PCE dramatically.

Graphical abstract: Naphthalene substituents bonded via the β-position: an extended conjugated moiety can achieve a decent trade-off between optical band gap and open circuit voltage in symmetry-breaking benzodithiophene-based polymer solar cells

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Publication details

The article was received on 02 Mar 2017, accepted on 11 Apr 2017 and first published on 12 Apr 2017


Article type: Paper
DOI: 10.1039/C7TA01905J
Citation: J. Mater. Chem. A, 2017,5, 9141-9147
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    Naphthalene substituents bonded via the β-position: an extended conjugated moiety can achieve a decent trade-off between optical band gap and open circuit voltage in symmetry-breaking benzodithiophene-based polymer solar cells

    D. Liu, C. Gu, J. Wang, D. Zhu, Y. Li, X. Bao and R. Yang, J. Mater. Chem. A, 2017, 5, 9141
    DOI: 10.1039/C7TA01905J

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