Organic photovoltaics: Understanding the preaggregation of polymer donors in solution and its morphological impact

Tonghui Wang, Jean Luc Bredas

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


In bulk-heterojunction organic solar cells, it is well established that the active-layer morphology significantly impacts device performance. However, morphology control remains very challenging. An interesting step in that direction was recently provided by the development of polymer donors that display a temperature-dependent aggregation behavior in solution; the aggregation characteristics were found indeed to play a determining role in the eventual active-layer morphology. Here, a combination of thermodynamic analyses, molecular dynamics simulations, and long-range corrected density functional theory calculations enables us (i) to establish the Flory-Huggins interaction parameter, χ, as a useful figure of merit that allows us to integrate the contributions from all inter-related molecular interactions and to describe the extent of polymer preaggregation in solution at room temperature; (ii) to correlate the χ values for various polymer solutions to the extent of polymer aggregation and the morphological characteristics of the active layers; and (iii) to assess how polymer-polymer and polymer-solvent intermolecular interactions contribute to the variations in χ values among different polymer solutions. We have chosen to examine four representative polymer donors (PBT4T-2OD, PBTff4T-2OD, PffBT4T-2OD, and PffBTff4T-2DT) in solution in chlorobenzene or dichlorobenzene. With χ as a robust bridge, our results provide an unprecedented, detailed description of the relationships among intermolecular interactions, extent of polymer solution aggregation, and morphological features of the active layers.

Original languageEnglish (US)
Pages (from-to)1822-1835
Number of pages14
JournalJournal of the American Chemical Society
Issue number4
StatePublished - Feb 3 2021
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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