Dye-sensitized solar cells (DSSCs) with quasi-solid-ion-gel electrolytes are fabricated using a 1-propyl-3-methyl imidazolium iodide (PMII) with a small amount of poly(styrene-block-ethyleneoxide-block-styrene) (SEOS) triblock copolymer. The interaction between the PMII and SEOS changes the liquid state of PMII into a solid state, and the interactions between the imidazolium cation of PMII and the ethyleneoxide of SEOS are confirmed by an ab initio method. The phase change of the electrolyte from an ionic liquid to a quasi-solid ion-gel in a DSSC slightly increases the photoconversion efficiency, and the DSSC containing an ion-gel maintains 92% of its efficiency under more than 1440 h of operation, which is higher than that with the ionic liquid as an electrolyte (78%) in this system. The addition of dendrons as a barrier-forming co-adsorbent increases the short-circuit current density (J(sc)) of the DSSC. Up to a 27% increase in the power conversion efficiency are achieved with the G5 dendron as the co-adsorbent. EIS and IPCE measurements show that the increase in J(sc) is due to the suppression of recombination by the surface coverage of the TiO2 particles. The photocurrent and the conversion efficiency for all DSSCs prepared with quasi-solid ion-gel electrolytes and dendron co-adsorbents are higher than those prepared with an ionic liquid. (C) 2011 Elsevier B.V. All rights reserved.