Carbazole-based ladder-type heptacylic arene with aliphatic side chains leading to enhanced efficiency of organic photovoltaics

Yen-Ju Cheng*, Jhong Sian Wu, Ping I. Shih, Chih Yu Chang, Pei Chi Jwo, Wei Shun Kao, Chain-Shu Hsu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

112 Scopus citations


By utilizing Friedel-Crafts cyclization, we have successfully designed and synthesized a ladder-type heptacyclic carbazole-dicyclopentathiophene (CDCT-C8) unit in which two outer thiophene subunits are covalently fastened to the central 2,7-carbazole core. The nitrogen-directing effect of the carbazole unit facilitates the intramolecular cyclization and thereby suppresses the acid-induced dehydration, allowing us to incorporate two octyl side chains on the cyclopentadiene rings in good chemical yield. The distannyl-CDCT-C8 building block was copolymerized with benzothiadiazole (BT), dithienylbenzothiadiazole (DTBT), dithienyldiketopyrrolopyrrole (DTDPP) and quinoxaline (QX) units by Stille polymerization to afford four alternating donor-acceptor copolymers, PCDCTBT-C8, PCDCTDTBT-C8, PCDCTDTDPP-C8 and PCDCTQX-C8, respectively. The device based on the PCDCTBT-C8:PC71BM (1:3 in wt%) blend exhibited a V oc of 0.74 V, a Jsc of 10.3 mA/cm2, a FF of 60%, delivering an impressive PCE of 4.6%. This value represents one of the best performances among carbazole-based conjugated polymers in the literatures. The corresponding PCDCTBT-C8:PC71BM blend showed a high hole mobility of 1.2 ×10-3 cm2 V-1 s-1, which is in good agreement with its high current density and fill factor. This improved performance is associated with the modification of the aliphatic side chains on the CDCT structure to optimize the interchain interactions for enhanced charge transporting. The devices based on PCDCTDTBT-C8, PCDCTDTDPP-C8 and PCDCTQX-C8 polymers also displayed promising efficiencies of 3.5%, 2.4%, and 1.8%, respectively.

Original languageEnglish
Pages (from-to)2361-2369
Number of pages9
JournalChemistry of Materials
Issue number9
StatePublished - 10 May 2011


  • Friedel-Crafts cyclization
  • carbazole
  • ladder-type
  • organic photovoltaics
  • polymerization


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