Effect of substitution positions of alkyl side chains in phenanthrodithiophene–isoindigo copolymers: The enhancement of crystallinity and control of molecular orders

Hiroki Mori, Shuto Hara, Ryota Toyama, Yuya Asanuma, Ryosuke Takahashi, Shuhei Nishinaga, Yasushi Nishihara

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The synthesis, characterization, and solar cell application of newly developed two semiconducting polymers containing phenanthro[1,2-b:8,7-b′]dithiophene (PDT) and an isoindigo (IID) unit are described. In addition, a relationship between substitution position of side chains and molecular weights of the polymers and their solar cell performance are also discussed. Because of the installation of alkyl side chains onto sterically less hindered positions, PDT-IID copolymers 12OD-2 and 8OD-2 have stronger intermolecular interaction than that of the previously reported copolymer 12OD. In low-Mn polymers 12OD-2 and 8OD-2 formed high-crystalline thin film with higher face-on ratio than that of 12OD, but their unsuitable large-scale phase separation suppressed their efficient photocurrent generation, leading to poor PCE of 2–3%. However, the surface morphology of 12OD-2 and 8OD-2 blended films are drastically improved by increasing Mn, which leads to the enhancement of Jsc and higher PCE of up to 4.3%. However, high-Mn polymers 12OD-2 and 8OD-2 formed high-crystalline film with about 10–15% lower face-on ratio than that of high-Mn polymer 12OD, leading to poor hole transporting ability, and thus lower Jsc and PCE. From this result, too much strong intermolecular interaction promotes the formation of unsuitable edge-on orientation in blended films.

Original languageEnglish
Pages (from-to)1757-1767
Number of pages11
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Volume56
Issue number15
DOIs
Publication statusPublished - Aug 1 2018

Keywords

  • isoindigo
  • molecular ordering
  • organic photovoltaics
  • phenanthrodithiophene
  • semiconducting polymer

ASJC Scopus subject areas

  • Polymers and Plastics
  • Organic Chemistry
  • Materials Chemistry

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