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Poly(thieno[3,2‑b]thiophene-alt-bithiazole): A D–A Copolymer Donor Showing Improved Photovoltaic Performance with Indene‑C60 Bisadduct Acceptor

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journal contribution
posted on 11.09.2012, 00:00 by Xia Guo, Maojie Zhang, Lijun Huo, Chaohua Cui, Yue Wu, Jianhui Hou, Yongfang Li
A new D–A copolymer, poly­(thieno­[3,2-b]­thiophene-alt-bithiazole) (PTTBTz), based on thieno­[3,2-b]­thiophene donor unit and bithiazole acceptor unit, was synthesized by the Pd-catalyzed Stille-coupling reaction for the application as donor material in polymer solar cells (PSCs). PTTBTz film possesses high thermal stability with 5% weight-loss temperature at 450 °C, a lower-lying HOMO energy level at −5.20 eV, a higher hole mobility of 6.45 × 10–3 cm2/(V s), and a crystalline structure. Photovoltaic performance of the polymer was investigated with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) or indene-C60 bisadduct (ICBA) as acceptor and with 3% DIO additive. The power conversion efficiency (PCE) of the PSC based on PTTBTz:ICBA (1:1 w/w) reached 5.35% with a high Voc of 1.03 V, a Jsc of 8.55 mA/cm2, and an FF of 0.608, whereas the PCE of the PSC based on PTTBTz:PC70BM (1:1 w/w) was 4.57% with a Voc of 0.82 V, a Jsc of 9.89 mA/cm2, and an FF of 0.563, under the illumination of AM1.5, 100 mW/cm2. PTTBTz is one of the D–A copolymers that shows better photovoltaic performance with ICBA as acceptor than PC70BM. PTTBTz/ICBA could be a promising front active layer for high-efficiency tandem PSC because of its high Voc.