Germanium- And silicon-substituted donor - Acceptor type copolymers: Effect of the bridging heteroatom on molecular packing and photovoltaic device performance

Jong Soo Kim, Zhuping Fei, Sebastian Wood, David T. James, Myungsun Sim, Kilwon Cho, Martin J. Heeney*, Ji Seon Kim

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

The effects of heteroatom substitution from a silicon atom to a germanium atom in donor-acceptor type low band gap copolymers, poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)- 4,7-diyl] (PSiBTBT) and poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d] germole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PGeBTBT), are studied. The optoelectronic and charge transport properties of these polymers are investigated with a particular focus on their use for organic photovoltaic (OPV) devices in blends with phenyl-C70-butyric acid methyl ester (PC70BM). It is found that the longer C-Ge bond length, in comparison to C-Si, modifies the molecular conformation and leads to a more planar chain conformation in PGeBTBT than PSiBTBT. This increase in molecular planarity leads to enhanced crystallinity and an increased preference for a face-on backbone orientation, thus leading to higher charge carrier mobility in the diode confi guration. These results provide important insight into the impact of the heavy atom substitution on the molecular packing and device performance of polymers based on the poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) backbone.

Original languageEnglish (US)
Article number1400527
JournalAdvanced Energy Materials
Volume4
Issue number18
DOIs
StatePublished - Dec 1 2014

Keywords

  • Donor- acceptor copolymers
  • Heavy atom substitution
  • Molecular packing
  • Organic solar cells
  • Raman spectroscopy

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Materials Science

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