Besides the establishment of a reliable processing technology for nc-DSC, the long term stability of the cells/modules has to be guaranteed. The overall stability of the cell is controlled by the intrinsic and extrinsic stability. The intrinsic stability is related to irreversible (photo-)electrochemical degradation of the dye and/or components of the electrolyte solution. Evaporation of the electrolyte solvent and intrusion of water and oxygen determine the extrinsic stability of the device. This requires hermetic sealing materials and reliable sealing methods, as discussed in Sect. 7.4. Standard testing according to IEC standards (environmental and accelerated) can be applied to nc-DSCs. It should be mentioned that these tests are mainly developed for inorganic solar cells and have to be tuned so that they stress dye solar cells and modules in a way which present standards do not.