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Issue 9, 2015
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Spectroscopically tracking charge separation in polymer : fullerene blends with a three-phase morphology

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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.

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

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Publication details

The article was received on 02 Jun 2015, accepted on 20 Jul 2015 and first published on 20 Jul 2015


Article type: Paper
DOI: 10.1039/C5EE01713K
Author version available: Download Author version (PDF)
Citation: Energy Environ. Sci., 2015,8, 2713-2724
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    Spectroscopically tracking charge separation in polymer : fullerene blends with a three-phase morphology

    J. K. Gallaher, S. K. K. Prasad, M. A. Uddin, T. Kim, J. Y. Kim, H. Y. Woo and J. M. Hodgkiss, Energy Environ. Sci., 2015, 8, 2713
    DOI: 10.1039/C5EE01713K

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