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

Amod Timalsina, Patrick E. Hartnett, Ferdinand S. Melkonyan*, Joseph Strzalka, Vari S. Reddy, Antonio Facchetti, Michael R. Wasielewski, Tobin J. Marks

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)5351-5361
Number of pages11
JournalJournal of Materials Chemistry A
Issue number11
StatePublished - 2017

ASJC Scopus subject areas

  • General Chemistry
  • Renewable Energy, Sustainability and the Environment
  • General Materials Science


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