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Issue 1, 2015
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Performance, morphology and photophysics of high open-circuit voltage, low band gap all-polymer solar cells

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Abstract

The microstructure and photophysics of low-band gap, all-polymer photovoltaic blends are presented. Blends are based on the donor polymer BFS4 (a dithienyl-benzo[1,2-b:4,5-b]dithiophene/5-fluoro-2,1,3-benzothiadiazole co-polymer) paired with the naphthalene diimide-based acceptor polymer P(NDI2OD-T2). Efficiencies of over 4% are demonstrated, with an open circuit voltage of greater than 0.9 V achieved. Transmission electron microscopy reveals a relatively coarse phase-separated morphology, with elongated domains up to 200 nm in width. Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) measurements reveal that the top surface of BFS4:P(NDI2OD-T2) blends is covered with a pure BFS4 capping layer. Depth profiling measurements confirm this vertical phase separation with a surface-directed spinodal decomposition wave observed. Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements confirm that BFS4 and P(NDI2OD-T2) are semicrystalline with both polymers retaining their semicrystalline nature when blended. Photoluminescence spectroscopy reveals incomplete photoluminescence quenching with as much as 30% of excitons failing to reach a donor/acceptor interface. Transient absorption spectroscopy measurements also find evidence for rapid geminate recombination.

Graphical abstract: Performance, morphology and photophysics of high open-circuit voltage, low band gap all-polymer solar cells

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Supplementary files

Article information


Submitted
26 Sep 2014
Accepted
10 Nov 2014
First published
11 Nov 2014

Energy Environ. Sci., 2015,8, 332-342
Article type
Paper

Performance, morphology and photophysics of high open-circuit voltage, low band gap all-polymer solar cells

K. D. Deshmukh, T. Qin, J. K. Gallaher, A. C. Y. Liu, E. Gann, K. O'Donnell, L. Thomsen, J. M. Hodgkiss, S. E. Watkins and C. R. McNeill, Energy Environ. Sci., 2015, 8, 332 DOI: 10.1039/C4EE03059A

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