Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering

Science Advances  15 Apr 2016:
Vol. 2, no. 4, e1501491
DOI: 10.1126/sciadv.1501491

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We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells.

  • Materials science
  • crystal structure
  • perovskite
  • solar cells
  • hole-transport material
  • spiro-OMeTAD
  • photovoltaics
  • solid-state dye-sensitized solar cell

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