CuS, CoS, and CuS/CoS onto fl uorine-doped tin oxide glass substrates were deposited to function as counter electrodes for polysulfi de redox reactions in CdS/CdSe quantum dot-sensitized solar cells (QDSSCs). Relative to a Pt electrode, the CuS, CoS, and CuS/CoS electrodes provide greater electrocatalytic activity, higher refl ectivity, and lower charge-transfer resistance. Measurements of fi ll factor and short-current density reveal that the electrocatalytic activities, refl ectivity, and internal resistance of counter electrodes play strong roles in determining the energy-conversion effi ciency ( η ) of the QDSSCs. Because the CuS/CoS electrode has a smaller internal resistance and higher refl ectivity relative to those of the CuS and CoS electrodes, it exhibits a higher fi ll factor and short-circuit current density. As a result, the QDSSC featuring a CuS/CoS electrode provides a higher value of η . Under illumination of one sun (100 mW cm − 2 ), the QDSSCs incorporating Pt, CuS, CoS, and CuS/CoS counter electrodes provide values of η of 3.0 ± 0.1, 3.3 ± 0.3, 3.8 ± 0.2, and 4.1 ± 0.2%, respectively.