Journal
CHEMISTRY OF MATERIALS
Volume 23, Issue 9, Pages 2361-2369Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm200041v
Keywords
Friedel-Crafts cyclization; carbazole; ladder-type; polymerization; organic photovoltaics
Funding
- National Science Council
- ATU, National Chiao Tung University
- Ministry of Education, Taiwan
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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 intrarnolecular cydization 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 Stile 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:PG7IBM (1:3 in wt%) blend exhibited a V-oc of 0.74 V, a J(sc) of 10.3 mA/cm(2), 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 x 10(-3) cm(2) 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.
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