Photocatalytic Oxidation of Triiodide in UVA-Exposed Dye-Sensitized Solar Cells

摘要

UVA irradiation of glass mounted dye-sensitized solar cells without UV filtration causes failure within 400 hours of light exposure. The failure mode is shown to relate to consumption of I_(3)~(-), which is directly related to TiO_(2) photo-catalysis. The onset of failure is easily determined from electrochemical impedance data where the recombination resistance of the TiO_(2)/electrolyte back reaction drops markedly prior to the onset of degradation. At the point of complete cell failure this impedance value then dramatically increases as there is no longer an interfacial reaction possible between the TiO_(2) and the I_(3)~(-) depleted electrolyte. Device failure is most rapid for cells under electrical load indicating that the degradation of the electrolyte is related to photogenerated hole production by excitation of the TiO_(2). Once depleted by UV exposure, the I_(3)~(-) can be regenerated by simple application of a reverse bias which can restore severely UV degraded devices to near original working conditions.