We demonstrate that a [Co(bpy)(3)](2+/3+) (PF6)(2/3) redox couple is an effective strategy for cost-effective and highly efficient dye-sensitized solar cells (DSSCs). Their high transmittance and large complex size make cobalt redox couples advantageous in back-illuminated devices. Furthermore, the use of thin TiO2 films, together with the naturally formed blocking layer at the outermost surface of Ti substrate, effectively alleviate the drawbacks of cobalt electrolyte. By virtue of these simultaneous effects, we achieve a highly promising power conversion efficiency of 7.12%. (C) 2014 Elsevier B.V. All rights reserved.