Spectroscopically tracking charge separation in polymer: fullerene blends with a three-phase morphology

Joseph K. Gallaher, Shyamal K.K. Prasad, Mohammad A. Uddin, Taehyo Kim, Jin Young Kim, Han Young Woo, Justin M. Hodgkiss

    Research output: Contribution to journalArticlepeer-review

    44 Citations (Scopus)

    Abstract

    The coexistence of intermixed amorphous polymer : fullerene phases alongside pure semicrystalline polymer and fullerene phases provides a plausible explanation for effective charge separation in organic photovoltaic blends by providing a cascaded energy landscape. We sought to test this proposal by spectroscopically tracking charge dynamics in 3-phase blends compared with binary counterparts and linking these dynamics to free charge yields. Our study applies broadband transient absorption spectroscopy to a series of closely related alternating thiophene-benzothiadiazole copolymers in which the tuned curvature of the polymer backbone controls the nature and degree of polymer-fullerene intermixing. Free charge generation is most efficient in the 3-phase morphology that features intimately mixed polymer : PCBM regions amongst neat polymer and PCBM phases. TA spectral dynamics and polarization anisotropy measurements reveal the sub-nanosecond migration of holes from intermixed to pure polymer regions of such blends. In contrast, 2-phase blends lack the spectral dynamics of this charge migration process and suffer from severe geminate recombination losses. These results provide valuable spectroscopic evidence for an efficient charge separation pathway that relies on the 3-phase morphology.

    Original languageEnglish
    Pages (from-to)2713-2724
    Number of pages12
    JournalEnergy and Environmental Science
    Volume8
    Issue number9
    DOIs
    Publication statusPublished - 2015 Sept 1

    Bibliographical note

    Publisher Copyright:
    © The Royal Society of Chemistry 2015.

    ASJC Scopus subject areas

    • Environmental Chemistry
    • Renewable Energy, Sustainability and the Environment
    • Nuclear Energy and Engineering
    • Pollution

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