The effect of the scattering layer in dye-sensitized solar cells employing a cobalt-based aqueous gel electrolyte

We developed an aqueous gel electrolyte based on the [Co(bpy)(3)](2+/3+) (bpy=2,2-bipyridine) redox mediator for use in n-type dye-sensitized solar cells. Application of this electrolyte in combination with titania nanoparticle-based photoanodes and mesoporous titania bead scattering layers resulted in devices with efficiencies of 4.1% under simulated AM 1.5 sunlight, compared with 3.5% for devices using scattering layers made from a commercial paste. This difference was largely a result of a 25% improvement in the short-circuit current density and was ascribed to lower diffusion resistance for the gel electrolyte within mesoporous TiO2 beads, as confirmed by electrochemical impedance spectroscopy. Transient photocurrent measurements identified mass-diffusion problems for DSCs employing the commercial TiO2 paste. Moreover, under continuous 1sun illumination, the devices based on an aqueous gel electrolyte displayed higher stability relative to those assembled with the corresponding liquid electrolyte.