Quasi-solid-state dye-sensitized solar cell (qss-DSSC) is a promising photovoltaic system, intended to solve the problem of electrolyte leakage and enhance the stability of this type of cell. The most challenging issue for thus type of cell is its relatively low power conversion efficiency (η), compared with that of its counter-part cell with a liquid electrolyte. In this study, various geometric structures of carbon, i.e., graphite, carbon nanotubes (CNT) and carbon spheres (CS) are added in an ionic liquid (IL) electrolyte to fabricate qss-DSSCs. Compare to the qss-DSSC with pristine IL electrolyte, the cells with graphite, CNT, and CS modified IL electrolyte show higher conversion efficiency. The highest photovoltaic performance of the cell with CS-modified IL electrolyte is explained on the basis of enhanced conductivity, increased diffusion coefficients of I- and I3- ions, and reduced charge transfer resistances, with reference to these parameters in the cases of pristine IL or ILs with graphite or CNT. Further comparative study is made among the performances of the qss-DSSCs using the CYC-B6S dye, reported by us previously, and the conventional N3 dye, both in the presence and absence of CS in the respective IL electrolytes. Finally, stability studies are made for these qss-DSSCs under continuous light soaking at 55 °C for 1,000 hours. All these studies demonstrate that the best performance (η = 6.16%) and stability (< 95%) are exhibited by the qss-DSSC with CS-modified IL electrolyte and CYC-B6S dye.