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Conjugated Polymer Consisting of Quinacridone and Benzothiadiazole as Donor Materials for Organic Photovoltaics: Coplanar Property of Polymer Backbone

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journal contribution
posted on 09.10.2012, 00:00 by Ho-Jun Song, Doo-Hun Kim, Eui-Jin Lee, Soo-Won Heo, Jang-Yong Lee, Doo-Kyung Moon
Highly soluble poly­[quinacridone-alt-benzothiadiazole] (PQCDTB) has been synthesized through the Suzuki coupling reaction by introducing planar quinacridone and highly absorbing benzothiadiazole. The PQCDTB dissolved in general organic solvents, and the Mn was 49.8 kg/mol. The optical band gap energy was 1.92 eV, which was similar to the band gap of benzothiadiazole. The HOMO and LUMO levels of PQCDTB were −5.24 eV and −3.32 eV, respectively. According to the XRD measurement, PQCDTB showed the formation of ordered lamellar structure as an out-of-plane peak (h00) by the alkyl side chain of quinacridone and conventional edge-on π- stacking. This study also evaluated the OPV characteristics by fabricating a bulk-heterojunction–type polymer solar cell. When PQCDTB and PC71BM were fabricated in a 1:1 weight ratio, the open-circuit voltage (VOC), short-circuit current (JSC), fill factor (FF), and power conversion efficiency (PCE) were 0.79 V, 5.6 mA cm–2, 55.8% and 2.5%, respectively. In particular, PQCDTB exhibited higher FFs compared with poly­[carbazole-alt-benzothiadiazole] (PCZDTB).