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

Xiaofeng Xu, Chuanfei Wang, Olof Backe, David James, Kim Bini, Eva Olsson, Mats R. Andersson, Mats Fahlman, Ergang Wang

    Research output: Contribution to journalArticle

    19 Citations (Scopus)

    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.

    Original languageEnglish
    Pages (from-to)4624-4633
    Number of pages10
    JournalPolymer Chemistry
    Volume6
    Issue number25
    DOIs
    Publication statusPublished - 2015

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