Correlation Between Charge Recombination and Lateral Hole-Hopping Kinetics in a Series of cis-Ru(phen′)(dcb)(NCS)2 Dye-Sensitized Solar Cells

Four complexes of the general form cis-Ru­(phen′)­(dcb)­(NCS)2, where dcb is 4,4′-(CO2H)2-2,2′-bipyridine and phen′ is 1,10-phenanthroline (phen), 4,7-(C6H5)2-phen (Ph2-phen), 4,7-(CH3)2-phen (Me2-phen), or 3,4,7,8-(CH3)4-phen (Me4-phen), were anchored to mesoporous TiO2 thin films for applications...

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Published in:ACS applied materials & interfaces 2017-10, Vol.9 (39), p.33446-33454
Main Authors: Sampaio, Renato N, Müller, Andressa V, Polo, André S, Meyer, Gerald J
Format: Article
Language:English
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Summary:Four complexes of the general form cis-Ru­(phen′)­(dcb)­(NCS)2, where dcb is 4,4′-(CO2H)2-2,2′-bipyridine and phen′ is 1,10-phenanthroline (phen), 4,7-(C6H5)2-phen (Ph2-phen), 4,7-(CH3)2-phen (Me2-phen), or 3,4,7,8-(CH3)4-phen (Me4-phen), were anchored to mesoporous TiO2 thin films for applications as sensitizers in dye-sensitized solar cells (DSSCs). The compounds displayed metal based reductions E o(RuIII/II) = 1.01 ± 0.05 V vs NHE and were potent reductants competent of excited-state electron transfer to TiO2 with yields ϕinj ≥ 0.75 in acetonitrile electrolytes. Average charge recombination rate constants, k cr, abstracted from nanosecond transient absorption measurements, and the apparent diffusion coefficients for lateral hole-hopping, abstracted from chronabsorptometry measurements, showed the same sensitizer dependency: Ru­(Me4-phen) > Ru­(Ph2-phen) > Ru­(Me2-phen) ≈ Ru­(phen). When used in operational solar cells, Ru­(Ph2-phen) was most optimal with an efficiency of (6.6 ± 0.5)% in ionic liquids under 1 sun illumination. The superior performance of Ru­(Ph2-phen) was traced to a higher injection yield and more efficient regeneration due to an unusually small sensitivity of k cr to the number of injected electrons.
ISSN:1944-8244
1944-8252
DOI:10.1021/acsami.7b01542