Effect of the π-conjugation length on the properties and photovoltaic performance of A-π-D-π-A type oligothiophenes with a 4,8-bis(thienyl)benzo[1,2-b:4,5-b′]dithiophene core

Ni Yin, Lilei Wang, Yi Lin, Jinduo Yi, Lingpeng Yan, Junyan Dou, Hai Bo Yang, Xin Zhao*, Chang Qi Ma

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)

Abstract

Benzo[1,2-b:4,5-b′]dithiophene (BDT) is an excellent building block for constructing π-conjugated molecules for the use in organic solar cells. In this paper, four 4,8-bis(5-alkyl-2-thienyl)benzo[1,2-b:4,5-b′]dithiophene (TBDT)-containing A-π-D-π-A-type small molecules (COOP-nHT-TBDT, n = 1, 2, 3, 4), having 2-cyano-3-octyloxy-3-oxo-1-propenyl (COOP) as terminal group and regioregular oligo(3-hexylthiophene) (nHT) as the π-conjugated bridge unit were synthesized. The optical and electrochemical properties of these compounds were systematically investigated. All these four compounds displayed broad absorption bands over 350-600 nm. The optical band gap becomes narrower (from 1.94 to 1.82 eV) and the HOMO energy levels increased (from -5.68 to -5.34 eV) with the increase of the length of the π-conjugated bridge. Organic solar cells using the synthesized compounds as the electron donor and PC61BM as the electron acceptor were fabricated and tested. Results showed that compounds with longer oligothiophene π-bridges have better power conversion efficiency and higher device stability. The device based on the quaterthiophenebridged compound 4 gave a highest power conversion efficiency of 5.62% with a VOC of 0.93 V, JSC of 9.60 mA·cm-2, and a FF of 0.63.

Original languageEnglish
Pages (from-to)1788-1797
Number of pages10
JournalBeilstein Journal of Organic Chemistry
Volume12
DOIs
Publication statusPublished - 10 Aug 2016

Keywords

  • A-π-D-π-A-type conjugated molecules
  • Benzodithiophene
  • Chain length effect
  • Organic solar cell
  • π-bridge

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