Enhanced Light Absorption in Fluorinated Ternary Small-Molecule Photovoltaics

Nicholas D. Eastham, Alexander S. Dudnik, Boris Harutyunyan, Thomas J. Aldrich, Matthew J. Leonardi, Eric F. Manley, Melanie R. Butler, Tobias Harschneck, Mark A Ratner, Lin X. Chen, Michael J. Bedzyk, Ferdinand S. Melkonyan, Antonio Facchetti, Robert P. H. Chang, Tobin J Marks

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Abstract

Using small-molecule donor (SMD) semiconductors in organic photovoltaics (OPVs) has historically afforded lower power conversion efficiencies (PCEs) than their polymeric counterparts. The PCE difference is attributed to shorter conjugated backbones, resulting in reduced intermolecular interactions. Here, a new pair of SMDs is synthesized based on the diketopyrrolopyrrole-benzodithiophene-diketopyrrolopyrrole (BDT-DPP2) skeleton but having fluorinated and fluorine-free aromatic side-chain substituents. Ternary OPVs having varied ratios of the two SMDs with PC61BM as the acceptor exhibit tunable open-circuit voltages (Vocs) between 0.833 and 0.944 V due to a fluorination-induced shift in energy levels and the electronic "alloy" formed from the miscibility of the two SMDs. A 15% increase in PCE is observed at the optimal ternary SMD ratio, with the short-circuit current density (Jsc) significantly increased to 9.18 mA/cm2. The origin of Jsc enhancement is analyzed via charge generation, transport, and diffuse reflectance measurements, and is attributed to increased optical absorption arising from a maximum in film crystallinity at this SMD ratio, observed by grazing incidence wide-angle X-ray scattering.

Original languageEnglish
Pages (from-to)1690-1697
Number of pages8
JournalACS Energy Letters
Volume2
Issue number7
DOIs
Publication statusPublished - Jul 14 2017

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ASJC Scopus subject areas

  • Chemistry (miscellaneous)
  • Energy Engineering and Power Technology
  • Fuel Technology
  • Renewable Energy, Sustainability and the Environment
  • Materials Chemistry

Cite this

Eastham, N. D., Dudnik, A. S., Harutyunyan, B., Aldrich, T. J., Leonardi, M. J., Manley, E. F., Butler, M. R., Harschneck, T., Ratner, M. A., Chen, L. X., Bedzyk, M. J., Melkonyan, F. S., Facchetti, A., Chang, R. P. H., & Marks, T. J. (2017). Enhanced Light Absorption in Fluorinated Ternary Small-Molecule Photovoltaics. ACS Energy Letters, 2(7), 1690-1697. https://doi.org/10.1021/acsenergylett.7b00486