Syntheses of New 3,6-Carbazole-Based Donor/ Acceptor Conjugated Copolymers for Optoelectronic Device Applications a Mei-Hsiu Lai, Jung-Hsun Tsai, Chu-Chen Chueh, Chih-Feng Wang, Wen-Chang Chen* Introduction Donor/acceptor (D/A) conjugated copolymers have attracted significant scientific interest recently since their electronic and optoelectronic properties can be manipu- lated through intramolecular charge transfer (ICT). [1–6] Such polymers may have potential applications in various organic electronic devices, such as light-emitting diodes (LEDs), [5–9] field-effect transistors, [10–16] and photovoltaic cells. [17–24] Carbazole-based conjugated polymers have been exten- sively studied for optoelectronic device applications because of their optical properties and good hole-transport- ing ability. [25–33] The hole-transporting characteristic of the carbazole moiety results from the electron-donating capabilities associated with the nitrogen in the carba- zole. [34–36] Moreover, the carbazole unit could be substi- tuted at the 3,6 or 2,7 positions to yield poly(3,6-carbazole) or poly(2,7-carbazole) derivatives. [37–38] Although the 3,6-linked carbazole led to a shorter conjugation length than the 2,7-linked carbazole, it offered the advantages of a much cheaper and straightforward synthesis. [38] Further- more, copolymers of 3,6-carbazole with fluorene, [27,28,34] thiophene, [40] and 3,4-ethylenedioxythiophene [41] were extensively reported for LED or electrochromic applications. Full Paper M.-H. Lai, J.-H. Tsai, C.-C. Chueh, C.-F. Wang, W.-C. Chen Department of Chemical Engineering, National Taiwan University, Taipei, 106, Taiwan ROC Fax: þ886 2 2362 3040; E-mail: chenwc@ntu.edu.tw W.-C. Chen Institute of Polymer Science and Engineering, National Taiwan University, Taipei 106, Taiwan a : Supporting information for this article is available at the bottom of the article’s abstract page, which can be accessed from the journal’s homepage at http://www.mcp-journal.de, or from the author. The syntheses, properties, and optoelectronic device characteristics of four new 3,6-carbazole- based donor/acceptor conjugated copolymers are reported. Such copolymers are used to explore the effects of acceptor strength and backbone coplanarity on the electronic and optoelectronic properties. The optical bandgaps of the studied copolymers are PCzQ (2.29 eV) > PCzDTQ (1.91 eV) > PCzTP (1.75 eV) > PCzDTTP (1.49 eV), which are much smaller than the parent poly(3,6-carbazole). The power conversion efficiency of the photovoltaic cells fabricated from blends of copolymer/PC 61 BM or PC 71 BM reached 1.01 and 1.73% by varying the film thickness or blend ratio. The experimental results suggest the potential application of 3,6-carbazole accep- tor conjugated copolymers in optoelectronic devices. Macromol. Chem. Phys. 2010, 211, 2017–2025 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/macp.201000234 2017