Dye Sensitized Solar Cells (DSCs) have achieved high power conversion efficiencies at a low cost. However, high stability remains an issue that impedes their commercialization and their degradation mechanisms are still under debate. In this study, we focus on accelerated thermal stressing of industrial DSCs at 85 degrees C for up to 290 h. The overall reduction of the DSCs efficiency (h) under this harsh stress is relatively small (about 20%) due to nearly 10% decrease in the Short Circuit Current (J(sc)) and Open Circuit Voltage (V-oc) and mainly occurs in the initial stage (within the first 54 h). The ageing mechanism is studied by combining the electrical, dc (J-V) and ac (impedance) characterization of the cells with their in-situ spectroscopic analysis under bias by micro-Raman. A sharp decrease in the recombination resistance at the sensitized photoelectrode/electrolyte interface is identified for the aged cell which is ascribed to trapping of triiodide species in the photoelectrode and accounts for the V-oc drop of the cells. J(sc) reduction could be justified by mitigation in the electron collection efficiency. (C) 2018 Elsevier Ltd. All rights reserved.