Dye-sensitized solar cells have been tested before, during, and after stress tests performed either under intense Xe-lamp illumination (equivalent to 1 sun up to 2.5 sun) or under thermal cycles between room T and 80 A degrees C. In-situ emission spectra and transient photovoltage decay curves have been taken to monitor the cell aging conditions. Incipient degradation phenomena in aged cells can be detected by changes in emission intensity, maximum photovoltage and in the time constant of photovoltage decay. UV-filtering of the Xe beam can prevent such cell degradation, provided the cell overheating is avoided.