New low band‐gap semiconducting polymers consisting of 5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine as a new acceptor unit for organic photovoltaic cells |
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Authors: | Ji‐Hoon Kim Hee Un Kim Chang Eun Song Moo‐Jin Park In‐Nam Kang Won Suk Shin Do‐Hoon Hwang |
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Institution: | 1. Department of Chemistry, and Chemistry Institute for Functional Materials, Pusan National University, , Busan, 609‐735 Republic of Korea;2. Department of Materials Science and Engineering KAIST, , Daejeon, 305‐701 Republic of Korea;3. Polymer Science and Engineering Program, KAIST, , Daejeon, 305‐701 Republic of Korea;4. Department of Chemistry, The Catholic University of Korea, , Gyeonggido, 90‐2 Republic of Korea;5. Energy Materials Research Center, Korea Research Institute of Chemical Technology, , Daejeon, 305‐343 Republic of Korea |
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Abstract: | A new carbazole‐based electron accepting unit, 5‐(2,7‐dibromo‐9H‐carbazol‐9‐yl)benzoa]phenazine (CBP), was newly designed and synthesized as the acceptor part of donor‐acceptor type low band‐gap polymers for polymer solar cells. The CBP was copolymerized with electron donating monomers such as benzo1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(2‐octyl‐2‐thienyl)‐benzo1,2‐b:4,5‐b′]dithiophene (BDTT) through Stille cross‐coupling polymerization, and produced two alternating copolymers, PBDT‐CBP and PBDTT‐CBP. An alternating copolymer (PBDT‐CBZ) consisted of 2,7‐dibromo‐9‐(heptadecan‐9‐yl)‐9H‐carbazole (CBZ) and BDT units was also synthesized for comparison. PBDT‐CBZ showed the maximum absorption at 430 nm and did not show absorption at wavelengths longer than 513 nm. However, CBP containing polymers (PBDT‐CBP and PBDTT‐CBP) showed a broad absorption between 300 and 850 nm due to the intramolecular charge transfer interaction between the electron donating and accepting blocks in the polymeric backbone. Bulk heterojunction photovoltaic devices were fabricated using the synthesized polymers as electron donors and 6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) as electron acceptor. One of these devices showed a power conversion efficiency of 2.33%, with an open‐circuit voltage of 0.81 V, a short‐circuit current of 6.97 mA/cm2, and a fill factor (FF) of 0.41 under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW/cm2). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2354–2365 |
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Keywords: | bulk‐heterojunction electron‐accepting carbazole monomer organic photovoltaic cells |
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