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Issue 25, 2015
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Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages

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Abstract

A new electron-deficient building block 5,9-di(thiophen-2-yl)-6H-pyrrolo[3,4-g]quinoxaline-6,8(7H)-dione (PQD) was synthesized via functionalizing the 6- and 7-positions of quinoxaline (Qx) with a dicarboxylic imide moiety. Side chain substitution on the PQD unit leads to good solubility which enables very high molecular weight copolymers to be attained. The fusion of two strong electron-withdrawing groups (Qx and dicarboxylic imide) makes the PQD unit a stronger electron-deficient moiety than if the unit had just one electron-withdrawing group, thus enhancing the intramolecular charge transfer between electron-rich and deficient units of the copolymer. Four PQD-based polymers were synthesized which feature deep-lying highest occupied molecular orbital (HOMO) levels and bathochromic absorption spectra when compared to PBDT–Qx and PBDT–TPD analogues. The copolymers incorporated with benzo[1,2-b:4,5-b‘]dithiophene (BDT) units show that the 1D and 2D structural variations of the side groups on the BDT unit are correlated with the device performance. As a result, the corresponding solar cells (ITO/PEDOT:PSS/polymer:PC71BM/LiF/Al) based on the four copolymers feature very high open-circuit voltages (Voc) of around 1.0 V. The copolymer PBDT-PQD1 attains the best power conversion efficiency of 4.9%, owing to its relatively high absorption intensity and suitable film morphology. The structure–property correlation demonstrates that the new PQD unit is a promising electron-deficient building block for efficient photovoltaic materials with high Voc.

Graphical abstract: Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages

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Publication details

The article was received on 18 Mar 2015, accepted on 11 May 2015 and first published on 11 May 2015


Article type: Paper
DOI: 10.1039/C5PY00394F
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Citation: Polym. Chem., 2015,6, 4624-4633
  • Open access: Creative Commons BY license
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    Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages

    X. Xu, C. Wang, O. Bäcke, D. I. James, K. Bini, E. Olsson, M. R. Andersson, M. Fahlman and E. Wang, Polym. Chem., 2015, 6, 4624
    DOI: 10.1039/C5PY00394F

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