Investigation of metal sulfide composites as counter electrodes for improved performance of quantum dot sensitized solar cells

Highlights: • The different metal sulfides were synthesized by simple chemical method. • CuS/CoS could increase the V oc value without sacrificing the J sc value. • The electron injection into the electrolyte was enhanced by CuS/CoS CE. • CuS/CoS CE showed the higher power conversion efficiency (5.22%). - Abstract: The electrochemical performance of counter electrodes (CEs) plays an important role for achieving high efficient quantum dot sensitized solar cells (QDSSCs). Considering the optical band gap energy of semiconductor materials and the V_oc of the QDSSCs is determined by the energy difference between the quasi-Fermi levels (_qE_f) of the anode and cathode, so in this work, we synthesized the different metal sulfides and their composites including CuS/CoS, CuS/NiS, CuS, CoS and NiS by chemical bath deposition (CBD) method and used as CEs of QDSSCs. The effect of different CEs on performance of cells were investigated, and the best power conversion efficiency (η) of 5.22% was achieved by CuS/CoS CE, which is higher than that of CuS/NiS, CuS, CoS and NiS (η = 2.56%, 4.73%, 2.23% and 1.62%). The improved cell efficiency was attributed to the excellent electrical conductivity and catalytic activity of CuS and CoS, respectively. The result indicated that the combination of different metal sulfide composites could increase open-circuit voltage (V_oc) value without sacrificing the short-circuit current (J_sc), and leaving good perspectives for significantly higher solar cell performances.