Development of a phenanthrodithiophene-difluorobenzoxadiazole copolymer exhibiting high open-circuit voltage in organic solar cells

Hiroki Mori, Ryosuke Takahashi, Yasushi Nishihara

    Research output: Contribution to journalArticlepeer-review

    1 Citation (Scopus)

    Abstract

    A phenanthrodithiophene (PDT)-difluorobenzoxadiazole (DFBO) copolymer, P-PDT-DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron-deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P-PDT-DFBO exhibits greater aggregation strength than previously reported for P-PDT-DFBT. The low-lying HOMO level of P-PDT-DFBO gave about 0.1 V higher open-circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide-angle X-ray diffraction analysis, P-PDT-DFBO formed a favorable face-on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P-PDT-DFBO-based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43%, due to its lower hole mobility than P-PDT-DFBT. One possible reason for poor performance may be the low crystallinity of P-PDT-DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long-range ordered structure.

    Original languageEnglish
    Pages (from-to)2646-2655
    Number of pages10
    JournalJournal of Polymer Science, Part A: Polymer Chemistry
    Volume56
    Issue number23
    DOIs
    Publication statusPublished - Dec 1 2018

    Keywords

    • Benzoxadiazole
    • Energy conversion
    • Phenanthrodithiophene
    • molecular ordering
    • open-circuit voltage
    • organic photovoltaics
    • polymers
    • semiconductors

    ASJC Scopus subject areas

    • Polymers and Plastics
    • Organic Chemistry
    • Materials Chemistry

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