The influence of alkoxy substitutions on the properties of diketopyrrolopyrrole-phenyl copolymers for solar cells.

Zandra George, Renee Kroon, Robert Gehlhaar, Gabin Gbabode, Angelica Lundin, Stefan Hellstrom, Christian Muller, Yves Geerts, Mats R. Andersson, Paul Heremans

    Research output: Contribution to journalArticlepeer-review

    6 Citations (Scopus)

    Abstract

    A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure.

    Original languageEnglish
    Pages (from-to)3022-3034
    Number of pages13
    JournalMaterials
    Volume6
    Issue number7
    DOIs
    Publication statusPublished - 2013

    Keywords

    • Conjugated polymers
    • Density functional theory (DFT)
    • DPP
    • Organic solar cells
    • Synthesis

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