High-efficiency and stable mesoscopic dye-sensitized solar cells (DSC) with more than a 10.5% photoelectrical conversion efficiency were obtained based on a high molar extinction coefficient ruthenium sensitizer and nonvolatile electrolyte. These devices are high photoelectrical efficiency over a large span of the visible light spectrum under direct sunlight and diffuse light conditions and low cost compared to the traditional solid-state crystalline silicon solar cells. The photovoltaic performance of DSCs is largely dependent on the kinetic competition between recapture of the injected electrons and the interception of the back electron transfer by regeneration of the sensitizer by the redox mediator. Highly efficient DSCs exhibiting unprecedented long-term stability under both light soaking and thermal stressing have been obtained using the K77 sensitizer in combination with a newly formulated nonvolatile organic-solvent-based electrolyte.