Enhanced electrocatalytic activity of vacuum thermal evaporated CuxS counter electrode for quantum dot-sensitized solar cells

• Vacuum thermal evaporation (VTE) is used to fabricate CuxS counter electrode (CE).
• QDSCs with VTE-CuxS CEs show a high efficiency of 3.16 ± 0.05% under one sun.
• The electrocatalytic activity of VTE-CuxS CE is higher than Pt and Brass-Cu2S CEs.
• VTE-CuxS CE exhibits good stability in polysulfide electrolyte.

Vacuum thermal evaporated CuxS (VTE-CuxS) film on fluorine-doped tin oxide substrate has been investigated as counter electrode (CE) for quantum dot-sensitized solar cells (QDSCs) with polysulfide electrolyte. The photovoltaic parameters of QDSCs show an obvious dependence on the annealing time of CuxS film, and the maximum power conversion efficiency of 3.16 ± 0.05% under one sun illumination (100 mW cm−2, AM 1.5 G) was obtained when the VTE-CuxS CE was annealed at 270 °C for 300 s (VTE-CuxS-300s CE). Electrochemical impedance spectroscopy, Tafel polarization, and cyclic voltammetry measurements have been employed to investigate the electrocatalytic activity of VTE-CuxS-300s CE. The electrocatalytic activity of the VTE-CuxS-300s CE is much higher than that of Pt CE, and is slightly higher than that of Cu2S CE in situ prepared on brass sheet. In particular, VTE-CuxS-300s CE holds high diffusion velocity of S2−/Sn2− in polysulfide electrolyte, and the stability of its electrocatalytic activity in polysulfide electrolyte is better than that of Pt and Brass-Cu2S CEs obviously.