Syntheses and characterization of carbazole based new low-band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Jaehong Kim, Sung Heum Park, Jinwoo Kim, Shinuk Cho, Youngeup Jin, Joo Young Shim, Hyunmin Shin, Sooncheol Kwon, Il Kim, Kwanghee Lee, Alan J. Heeger, Hongsuk Suh

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

Newly designed 2H-benzimidazole derivatives which have solubility groups at 2-position have been synthesized and incorporated into two highly soluble carbazole based alternating copolymers, poly[2,7-(9-(1′-octylnonyl)-9H- carbazole)-alt-5,5-(4′,7′-di(thien-2-yl)-2H-benzimidazole-2′- spirocyclohexane)] (PCDTCHBI) and poly[2,7-(9-(1′-octylnonyl)-9H- carbazole)-alt-5,5-(4′,7′-di(thien-2-yl)-2H-benzimidazole-2′- spiro-4″-((2‴-ethylhexyl)oxy)-cyclohexane)] (PCDTEHOCHBI) for photovoltaic application. These alternating copolymers show low-band gap properties caused by internal charge transfer from an electron-rich unit to an electron-deficient moiety. HOMO and LUMO levels are -5.53 and -3.86 eV for PCDTCHBI, and -5.49 and -3.84 eV for PCDTEHOCHBI, respectively. Optical band gaps of PCDTCHBI and PCDTEHOCHBI are 1.67 and 1.65 eV, respectively. The new carbazole based the 2H-benzimidazole polymers show 0.11-0.13 eV lower values of band gaps as compared to that of carbazole based benzothiadiazole polymer, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′, 7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), while keeping nearly the same deep HOMO levels. The power conversion efficiencies of PCDTCHBI and PCDTEHOCHBI blended with [6,6]phenyl-C 71-butyric acid methyl ester (PC71BM) are 1.03 and 1.15%, respectively.

Original languageEnglish
Pages (from-to)369-380
Number of pages12
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Volume49
Issue number2
DOIs
StatePublished - 15 Jan 2011

Keywords

  • 2H-benzimidazole
  • conjugated polymers
  • copolymerization
  • low-band gap polymer
  • polymer solar cell
  • thin films

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