Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene

Sara Marina, Alberto D. Scaccabarozzi, Edgar Gutierrez-Fernandez, Eduardo Solano, Aditi Khirbat, Laura Ciammaruchi, Amaia Iturrospe, Alex Balzer, Liyang Yu, Elena Gabirondo, Xavier Monnier, Haritz Sardon, Thomas D. Anthopoulos, Mario Caironi, Mariano Campoy-Quiles, Christian Müller, Daniele Cangialosi, Natalie Stingelin, Jaime Martin

Research output: Contribution to journalArticlepeer-review

Abstract

Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.
Original languageEnglish (US)
Pages (from-to)2103784
JournalAdvanced Functional Materials
DOIs
StatePublished - May 13 2021

ASJC Scopus subject areas

  • Biomaterials
  • Electrochemistry
  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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