D鈥揂1鈥揇鈥揂2 Copolymers with Extended Donor Segments for Efficient Polymer Solar Cells

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• 作者：Qiang Tao ; Yuxin Xia ; Xiaofeng Xu ; Svante Hedstr枚m ; Olof B盲cke ; David I. James ; Petter Persson ; Eva Olsson ; Olle Ingan盲s ; Lintao Hou ; Weiguo Zhu ; Ergang Wang
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：February 24, 2015
• 年：2015
• 卷：48
• 期：4
• 页码：1009-1016
• 全文大小：572K
• ISSN：1520-5835

文摘

Typically a donor鈥揳cceptor (D鈥揂) design strategy is used for engineering the bandgap of polymers for solar cells. However, in this work, a series of alternating D鈥揂₁鈥揇鈥揂₂ copolymers PnTQTI(F) were synthesized and characterized with oligothiophenes (nT, n = 1, 2, 3) as the donor and two electron-deficient moieties, quinoxaline and isoindigo, as the acceptors in the repeating unit. We have studied the influence of the donor segments with different numbers of thiophene units and the effect of the addition of fluorine to the quinoxaline unit of the D鈥揂₁鈥揇鈥揂₂ polymers. The photophysical, electrochemical, and photovoltaic properties of the polymers were examined via a range of techniques and related to theoretical simulations. On increasing the length of the donor thiophene units, broader absorption spectra were observed in addition to a sequential increase in HOMO levels, while the LUMO levels displayed very small variations. The addition of fluorine to the quinoxaline unit not only decreased the HOMO levels of the resulting polymers but also enhanced the absorption coefficients. A superior photovoltaic performance was observed for the P3TQTI-F-based device with a power conversion efficiency (PCE) of 7.0%, which is the highest efficiency for alternating D鈥揂₁鈥揇鈥揂₂ polymers reported to date. The structure鈥損roperty correlations of the PnTQTI(F) polymers demonstrate that varying of the length of the donor segments is a valuable method for designing high-performance D鈥揂₁鈥揇鈥揂₂ copolymers and highlight the promising nature of D鈥揂₁鈥揇鈥揂₂ copolymers for efficient bulk-heterojunction solar cells.