Novel Blue Organic Dye for Dye-Sensitized Solar Cells Achieving High Efficiency in Cobalt-Based Electrolytes and by Co-Sensitization

Blue and green dyes as well as NIR-absorbing dyes have attracted great interest because of their excellent ability of absorbing the incident photons in the red and near-infrared range region. A novel blue D−π–A dye (Dyenamo Blue), based on the diketopyrrolopyrrole (DPP)-core, has been designed and synthesized. Assembled with the cobalt bipyridine-based electrolytes, the device with Dyenamo Blue achieved a satisfying efficiency of 7.3% under one sun (AM1.5 G). The co-sensitization strategy was further applied on this blue organic dye together with a red D−π–A dye (D35). The successful co-sensitization outperformed a panchromatic light absorption and improved the photocurrent density; this in addition to the open-circuit potential result in an efficiency of 8.7%. The extended absorption of the sensitization and the slower recombination reaction between the blue dye and TiO 2 surface inhibited by the additional red sensitizer could be the two main reasons for the higher performance. In conclusion, from the results, the highly efficient cobalt-based DSSCs could be achieved with the co-sensitization between red and blue D−π–A organic dyes with a proper design, which showed us the possibility of applying this strategy for future high-performance solar cells.