Side-chain-bulk effects on the molecular packing and photovoltaic performance of benzotrithiophene-benzooxadiazole conjugated copolymers

Shang Che Lan, Chiao Kai Chang, Yi Chien Wang, Kung-Hwa Wei*

*Corresponding author for this work

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Two alternating donor-acceptor conjugated polymers, PBTTBO-C13C11 and PBTTBO-C13C8, comprising 5-alkylbenzo[1,2-b:3,4-b:5,6-d]trithiophene (BTT) as the donor and 4,7-bis(4-dodecylthien-2-yl)benzo[1,2,5]oxadiazole (BO) as the acceptor, with different alkyl side-chain architectures on their BTT units are synthesized, and their bulk heterojunction photovoltaic properties when blended with the fullerene PC71BM are characterized. Even a slight change in the length of the alkyl chain of the BTT units influences the steric bulk to such a degree that it substantially affects the molecular packing of the polymers and the performance of their photovoltaic devices. The bulkier side chains of the polymer PBTTBO-C13C11 not only prevent its crystallization, but also suppress its light-absorption coefficient relative to that of PBTTBO-C13C8, as evidenced by X-ray diffraction and UV/Vis absorption studies, presumably because of weakened intermolecular interactions. Moreover, the polymer bearing bulkier side chains, PBTTBO-C13C11, is less miscible with PC71BM than PBTTBO-C13C8, and this characteristic determines the morphology of their annealed blended films, as shown by TEM studies. The best efficiency is obtained with a device containing an annealed PBTTBO-C13C8/PC71BM (1/2 w/w) active layer that was maintained at 120 C for 10 min, which shows a power conversion efficiency of 6.2 %, an open-circuit voltage of 0.75 V, a short-circuit current density of 12.6 mA cm-2, and a fill factor of 66 %.

Original languageEnglish
Pages (from-to)1268-1274
Number of pages7
JournalChemPhysChem
Volume16
Issue number6
DOIs
StatePublished - 27 Apr 2015

Keywords

  • bulk heterojunctions
  • conjugated polymers
  • donor-acceptor systems
  • side-chain engineering
  • solar cells

Fingerprint Dive into the research topics of 'Side-chain-bulk effects on the molecular packing and photovoltaic performance of benzotrithiophene-benzooxadiazole conjugated copolymers'. Together they form a unique fingerprint.

  • Cite this