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 1 sun illumination, the devices based on an aqueous gel electrolyte displayed higher stability relative to those assembled with the corresponding liquid electrolyte.