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Issue 11, 2017
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New donor polymer with tetrafluorinated blocks for enhanced performance in perylenediimide-based solar cells

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Abstract

The synthesis of a new tetrafluorinated semiconducting donor polymer, poly[(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophene-2-yl)-benzo[1,2-b:4,5-b′]dithiophene)-alt-(5,6-difluoro-4,7-(4-(2-ethylhexyl)-dithien-2-yl-2,1,3-benzothiadiazole)] (PBTZF4), and its photovoltaic performance in bulk heterojunction (BHJ) blends with the non-fullerene molecular acceptor [1,2:3,4]-bis-[N,N′-bis-1-pentylhexyl-perylenediimide-1,12-yl]-benzene (bPDI2P), are reported. PBTZF4:bPDI2P solar cells exhibit a high open circuit voltage (Voc) of 1.118 V, a short circuit current density (Jsc) of 10.02 mA cm−2, and a fill factor (FF) of 49.5%, affording a power conversion efficiency (PCE) of 5.55%. Interestingly, a lower PCE of 3.68% is obtained with the difluorinated analogue, poly[(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b:4,5-b′]dithiophene)-alt-(5,6-difluoro-4,7-(4-(2-ethyl-hexyl)-dithien-2-yl-2,1,3-benzothiadiazole)] (PBTZF2). Both PBTZF4:bPDI2P and PBTZF2:bPDI2P cells benefit from complementary (donor/acceptor) light absorption and very low geminate recombination, with bimolecular recombination being the dominant loss mechanism, as established by femtosecond transient absorption spectroscopy. DFT computation and physicochemical characterization data argue that the “additional” tetrafluorination planarizes the PBTZF4 backbone and enhances aggregation versusPBTZF2, affording superior charge carrier transport as assayed by field-effect mobility. In addition, fluorine-originated HOMO stabilization, −5.41 eV for PBTZF4versus −5.33 eV for PBTZF2, and a superior blend microstructure afford a higher PBTZF4:bPDI2P solar cell PCE versusPBTZF2:bPDI2P.

Graphical abstract: New donor polymer with tetrafluorinated blocks for enhanced performance in perylenediimide-based solar cells

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Publication details

The article was received on 03 Jan 2017, accepted on 08 Feb 2017 and first published on 09 Feb 2017


Article type: Paper
DOI: 10.1039/C7TA00063D
Citation: J. Mater. Chem. A, 2017,5, 5351-5361
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    New donor polymer with tetrafluorinated blocks for enhanced performance in perylenediimide-based solar cells

    A. Timalsina, P. E. Hartnett, F. S. Melkonyan, J. Strzalka, V. S. Reddy, A. Facchetti, M. R. Wasielewski and T. J. Marks, J. Mater. Chem. A, 2017, 5, 5351
    DOI: 10.1039/C7TA00063D

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