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

Kedar D. Deshmukh, Tianshi Qin, Joseph K. Gallaher, Amelia Chi Ying Liu, Eliot Gann, Kane Michael O'Donnell, Lars Thomsen, Justin M. Hodgkiss, Scott Edward Watkins, Christopher R. McNeill

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113 Citations (Scopus)


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(NDI2ODT2). 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.
Original languageEnglish
Pages (from-to)332 - 342
Number of pages11
JournalEnergy & Environmental Science
Issue number1
Publication statusPublished - 2015

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