High efficiency solid-state dye-sensitized solar cells using a cobalt(II/III) redox mediator

Improvement in the mass transport of the considerably large sized cobalt(ii/iii) complexes, particularly in a high viscosity electrolyte, is crucial for solid-state dye-sensitized solar cells (SS-DSCs) to reach a reliable high efficiency for practical applications. In this study, titania nanorod aggregates (TNA) with a large specific surface area and well-developed crystalline network were utilized as photoanode building blocks for application in a cobalt(ii/iii) tris(2′2-bipyridine) complexes-based solid-state electrolyte. An initial efficiency excess of 7.1% and a long term stable efficiency of approximately 8.0% were achieved under full sun illumination by the freshly assembled and aged TNA SS-DSCs, respectively. This represents dramatic enhancements of nearly 35% and 100% against the SS-DSCs prepared from two standard TiO₂ nanoparticle samples-CCIC (approx. 5.9%) and Degussa P25 (approx. 4.0%), correspondingly. The TNA is characterised by a combination of mesopores within each aggregate and macro inter-aggregate voids, a high specific surface area and great light scattering ability; such features make the aggregates superior photoanode building blocks for their application in bulky cobalt redox mediator based SS-DSCs systems.