Highly Electrocatalytic Cu2ZnSn(S1-xSex)4 Counter Electrodes for Quantum-Dot-Sensitized Solar Cells

Traditional Pt counter electrode in quantum-dot-sensitized solar cells suffers from a low electrocatalytic activity and instability due to irreversible surface adsorption of sulfur species incurred while regenerating polysulfide (S-n(2-)/S2-) electrolytes. To overcome such constraints, chemically synthesized Cu2ZnSn(S1-xSex)(4) nanocrystals were evaluated as an alternative to Pt. The resulting chalcogenides exhibited remarkable electrocatalytic activities for reduction of polysulfide (S-n(2-)) to sulfide (S2-), which were dictated by the ratios of S/Se. In this study, a quantum dot sensitized solar cell constructed with Cu2ZnSn(S0.5Se0.5)(4) as a counter electrode showed the highest energy conversion efficiency of 3.01%, which was even higher than that using Pt (1.24%). The compositional variations in between Cu2ZnSnS4 (x = 0) and Cu2ZnSnSe4 (x = 1) revealed that the solar cell performances were closely related to a difference in electrocatalytic activities for polysulfide reduction governed by the S/Se ratios.