43 research outputs found
Photoelectrochemical response of DSSCs under prolonged reverse bias and conduction band lowering in Ru-complex sensitized TiO2
TiO2-based DSSCs sensitized with the Ru-dyes N719 and Z907, have been subjected
to prolonged reverse bias 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 have been followed
by means of the periodical recording of I-V curves, electrochemical impedance spectra,
charge extraction measurements and photovoltage decays at the various stages of cell
aging. Beside the expected decrease of the concentration of I3- during RB aging, the
measurements evidenced for both DSSCs a surprising shift of the conduction band
edge toward lower energies and a concomitant slowing down of the recombination
process with the electrolyte. This led to a noticeable improvement of 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, produced during the RB aging, on the TiO2 surface