Quantum Dot-Sensitized Solar Cells Featuring CuS/CoS Electrodes Provide 4.1% Efficiency

CuS, CoS, and CuS/CoS onto fluorine‐doped tin oxide glass substrates were deposited to function as counter electrodes for polysulfide 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 reflectivity, and lower charge‐transfer resistance. Measurements of fill factor and short‐current density reveal that the electrocatalytic activities, reflectivity, and internal resistance of counter electrodes play strong roles in determining the energy‐conversion efficiency (η) of the QDSSCs. Because the CuS/CoS electrode has a smaller internal resistance and higher reflectivity relative to those of the CuS and CoS electrodes, it exhibits a higher fill 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. Quantum dot‐sensitized solar cells featuring CuS/CoS relative to Pt counter electrodes provide greater energy conversion efficiency (4.1 ± 0.2% vs. 3.0 ± 0.1%) and are more stable. The improved performance is attributed to the greater electrocatalytic activity, higher reflectivity, and lower charge‐transfer resistance of these electrode materials relative to platinum.