We explored quasi-solid electrolyte containing nanoclay and iodide/triiodide (I-/I-3(-)) redox mediator in dye sensitized solar cells (DSSCs). Compared with traditional iodine based liquid electrolyte, nanoclay-based quasi-solid electrolyte provided similar conversion efficiency and carrier diffusivity. In addition, the nanoclay in the electrolyte increases thermal stability and suppresses aging behavior. The rheology measurement showed that the enhancement was attributed to the gelation of the quasi-solid electrolyte. The addition of nanoclay increased the optimum amount of iodine in the electrolyte, since a partial adsorption of iodide ions on the positive surface of the nanoclay reduces ion concentration in the electrolyte and changes the carrier transfer path. This adsorption increased in the quantity of the iodide to optimize the performance of the quasi-solid electrolyte. We have found that the charge transport in the electrolyte occurs via two parallel processes: normal physical diffusion and grotthus-type bond exchange. (C) 2014 Elsevier Ltd. All rights reserved.