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Photoelectrochemical response of DSSCs under prolonged reverse bias and conduction band lowering in Ru-complex-sensitized TiO2

: Pumiglia, D.; Giustini, M.; Dini, D.; Decker, F.; Lanuti, A.; Mastroianni, S.; Veyres, S.; Caprioli, F.


ChemElectroChem 1 (2014), Nr.8, S.1388-1394
ISSN: 2196-0216
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Farbstoff-; Organische und Neuartige Solarzellen; Farbstoff- und Perowskitsolarzellen; Charakterisierung von Prozess- und Silicium-Materialien; bias; TiO2; DSSCs; photochemistry; ruthenium

TiO2-based dye-sensitized solar cells (DSSCs) sensitized with the Ru-dyes N719 and Z907, are subjected to prolonged reverse bias (RB) by imposing a constant current density of 25 mA cm(-2) for up to 1000 h. The temporal changes of the DSSCs during the aging process are followed by the periodical recording of current-voltage curves, electrochemical impedance spectra, charge extraction measurements, and photovoltage decays at the various stages of cell aging. Beside the expected decrease in the concentration of I-3(-) during RB aging, the measurements show a surprising shift of the conduction band edge toward lower energies and a concomitant slowing down of the recombination process with the electrolyte for both DSSCs. This leads to a noticeable improvement in the energy conversion efficiency under low illumination conditions. These unexpected results are discussed on the basis of recent literature reports and attributed tentatively to the adsorption of H+ ions, which are produced during the RB aging, onto the TiO2 surface.