Large-area and highly durable dye-sensitized solar cells with current collecting silver grid and their submodules were fabricated. Ionic liquids were used as the nonvolatile solvent for electrolytes instead of conventional organic solvents. In the case of applying ionic liquid-based electrolyte, no obvious leakage of solvent and/or solute, such as ionic liquid itself, iodine and iodide salt, was detected on keeping the cell at 85 °C for several thousand hours. Optimization of protection materials for the grid, improvement of sealant, and modifying the sealing methods lead significant enhancement of stability of the cell. On the other hand, it was clarified that moisture intrusion into the cell during the manufacturing process deteriorated thermal stability. Several accelerated endurance tests were carried out to investigate the reliability of dye-sensitized solar cells and modules under the conditions by referring JIS-C8938 standard, which were designated for amorphous silicon solar cells and modules. Our cells and modules showed almost no degradation of the performance under the heat and humidity environment (85 °C, 85% RH) for more than 1,000 hours and under the heat and cool cycle stress (–40 °C and 90 °C) for more than 200 cycles.