Iodine-free nanocomposite gel electrolytes for quasi-solid-state dye-sensitized solar cells

Iodine-free quasi-solid-state electrolytes were developed for dye-sensitized solar cells (DSSCs) by removing I-2 from the conventional I-/I-3(-) redox electrolyte and gelling the electrolyte with metal oxide nanoparticles. The inorganic nanoparticles played a dual role of gelling agent and charge transport enhancer. The removal of I-2 improved the long-term stability of DSSCs, but reduced the ionic diffusivity of electrolyte and thus the solar-to electricity efficiency of DSSCs. By introducing a suitable nanoparticle gelator into the electrolyte, the ionic diffusivity and the interfacial charge transfer could be enhanced due to the formation of 3-D networks that facilitate Grotthuss-type ion exchange. Three different metal oxide nanoparticles (SiO2, TiO2, and ZnO) were evaluated, and the best performance was obtained by TiO2 nanoparticles. The I-2-free quasi-solid-state DSSCs gelled by 15% TiO2 achieved an efficiency of 8.00% vs. a 6.94% efficiency attained by the I-2-free liquid-state reference cells. The I-2-free quasi-solid-state DSSCs gelled by 15% TiO2 also exhibited good long-term at-rest stability with an estimated life span of five to six years under ambient condition based on an accelerated stability test performed at 65 degrees C with 65% relative humidity.