Suppressing Defect Formation Pathways in the Direct C-H Arylation Polymerization of Photovoltaic Copolymers

Thomas J. Aldrich, Alexander S. Dudnik, Nicholas D. Eastham, Eric F. Manley, Lin X. Chen*, Robert P.H. Chang, Ferdinand S. Melkonyan, Antonio Facchetti, Tobin J. Marks

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


Direct C-H arylation polymerization (DARP) holds great promise for the green, atom-efficient synthesis of π-conjugated copolymers for use in high-performance polymer solar cells (PSCs). However, C-H arylation regioselectivity control for monomers containing multiple reactive aryl C-H bonds is not well understood, and nonselective reactivity results in material defects with unknown effects on PSC performance. Here, the effects of reaction conditions on copolymer molecular mass, dispersity, and PSC performance as well as defect formation pathways occurring during the DARP synthesis of an archetypal benzodithiophene-alt-diketopyrrolopyrrole copolymer, PBDTT-DPP, are scrutinized. Small molecule model studies analyzed by HPLC-HRMS elucidate the effects of DARP conditions on trace chemical defect (primarily hydrodehalogenation and β-C-H arylation) formation. Copolymer branching arising from nonselective β-C-H arylation of monomers at the polymer chain end is identified as the principal photovoltaically deleterious defect. Fine-tuning the DARP reaction conditions reduces branching densities to below 1%, with an exceptional C-H regioselectivity of >110:1. The optimal copolymers achieve superior PSC performance versus defect-rich DARP-derived copolymers and rival those from Stille polycondensations.

Original languageEnglish (US)
Pages (from-to)9140-9155
Number of pages16
Issue number22
StatePublished - Nov 27 2018

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry


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