2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Mohammad Afsar Uddin, Taehyo Kim, Seungjib Yum, Hyosung Choi, Sungu Hwang, Jin Young Kim, Han Young Woo

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Three kinds of donor-acceptor (D-A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be -5.72, -5.67 and -5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (VOC) in the range, 0.86-0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high VOC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (JSC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC71BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron-hole recombination at the polymer/PC71BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC71BM. The PCBTTPD:PC71BM device showed the best PCE of 3.42% with a VOC and JSC of 0.86 V and 7.79 mA cm-2, respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high VOC and sufficient energy offset for ensuring efficient hole transfer from PC71BM to the polymer.

Original languageEnglish
Pages (from-to)654-661
Number of pages8
JournalCurrent Applied Physics
Volume15
Issue number5
DOIs
Publication statusPublished - 2015 Jan 1
Externally publishedYes

Keywords

  • Carbazole
  • Charge recombination
  • Photovoltaic polymer
  • Polymer solar cell
  • Thienopyrroledione

ASJC Scopus subject areas

  • Materials Science(all)
  • Physics and Astronomy(all)

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