Incorporation of ester groups into low band-gap diketopyrrolopyrrole containing polymers for solar cell applications

Xiaolian Hu, Lijian Zuo, Weifei Fu, Thue Trofod Larsen-Olsen, Martin Helgesen, Eva Bundgaard, Ole Hagemann, Minmin Shi, Frederik C Krebs, Hongzheng Chen

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To increase the open circuit voltage (VOC) of polymer solar cells based on diketopyrrolopyrrole (DPP) containing polymers, the weakly electron-withdrawing thiophene-3,4-dicarboxylate unit was introduced into the polymer backbone. Two ester group functionalized DPP containing polymers, PCTDPP with a random structure and PDCTDPP with a regular structure, were designed and synthesized by the Stille coupling reaction. The resulting copolymers exhibit broad and strong absorption bands from 350 to 1000 nm with low optical band gaps below 1.40 eV. Through cyclic voltammetry measurements, it is found that regular PDCTDPP's HOMO energy level is 0.18 V lower than that of the corresponding random PCTDPP (−5.14 eV for PCTDPP and −5.32 eV for PDCTDPP). Preliminary photovoltaic properties of the copolymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor were investigated. The PSC based on a PCTDPP:PCBM blend shows a power conversion efficiency (PCE) up to 3.52%, with a VOC of 0.66 V, a short circuit current (ISC) of 8.53 mA cm−2, and a fill factor (FF) of 0.63. For the PDCTDPP:PCBM blend, the highest VOC reaches a value of 0.84 V, and a final PCE (0.92%) is limited by the poor hole mobility of the active layer.
Original languageEnglish
JournalJournal of Materials Chemistry
Issue number31
Pages (from-to)15710-15716
Publication statusPublished - 2012

Bibliographical note

This work was supported by the National Natural Science Foundation of China (nos. 20774083, 50990063, 51073135) and Zhejiang Province Natural Science Foundation (no. Y407101). Also support from the Danish National Research Foundation and the National Natural Science Foundation of China (Grant no. 51011130028) for the Danish-Chinese Center for Organic based Photovoltaic Cells, within which this work was performed. The work was also partly supported by Developing Program of Zhejiang Province Key Scientific and Technical Innovation Team (no. 2009R50004), the Fundamental Research Funds for the Central Universities (no. 2010QNA4013), and the National High Technology Research and Development Program of China (863 Program) (no. 2011AA050520)


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