Improved Photovoltaic Properties of Donor鈥揂cceptor Copolymers by Introducing Quinoxalino[2,3-b鈥瞉porphyrin as a Light-Harvesting Unit

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• 作者：Liwei Wang ; Shaowei Shi ; Di Ma ; Song Chen ; Chen Gao ; Meng Wang ; Keli Shi ; Yongfang Li ; Xiaoyu Li ; Haiqiao Wang
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：January 13, 2015
• 年：2015
• 卷：48
• 期：1
• 页码：287-296
• 全文大小：495K
• ISSN：1520-5835

文摘

Donor鈥揳cceptor (D鈥揂) copolymerization is an effective approach to construct low bandgap polymers with tunable electronic energy levels for the application as donor materials in polymer solar cells (PSCs). Usually, D鈥揂 copolymers possess an intramolecular charge transfer absorption band at long wavelength direction, so that the absorption of the polymers is broadened. However, absorption at short wavelength direction is also important and should be broadened and enhanced to increase the short-circuit current density (J_sc) of the PSCs. In this study, a series of low bandgap conjugated polymers, P(QP4-BT-DPP1), P(QP1-BT-DPP1), and P(QP1-BT-DPP4), based on two acceptor units quinoxalino[2,3-b鈥瞉porphyrin (QP) and diketopyrrolopyrrole (DPP) connected by oligothiophene donor units, were designed and synthesized by palladium-catalyzed Stille-coupling polymerization. As a complementary light-harvesting unit, QP was first introduced into the D鈥揂 conjugated polymers for improving the photovoltaic performance of PSCs. The incorporation of QP broadened and enhanced the absorptions of short wavelength photons as well as kept the well-tuned electronic energy levels and bandgap of the pristine D鈥揂 copolymer. Moreover, para-linked QP improved coplanarity and extended 蟺-conjugation along the polymer backbone. As a result, P(QP1-BT-DPP4) with a proper feed ratio (10 mol %) of QP showed an increased J_sc of 11.85 mA/cm² without sacrificing open-circuit voltage (V_oc) or fill factor (FF) of the photovoltaic devices. Preliminary photovoltaic devices showed a highest power conversion efficiency of 5.07%, which was 3 times higher than that of the PSC fabricated from the pristine D鈥揂 copolymer. This study provides a promising approach to circumvent the trade-off between light absorption and electronic energy levels so as to balance the J_sc, V_oc, and FF by introducing a third component into well-performed D鈥揂 conjugated copolymers for achieving high performance PSCs.