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2014
Journal Article
Titel
Photoelectrochemical response of DSSCs under prolonged reverse bias and conduction band lowering in Ru-complex-sensitized TiO2
Abstract
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.