ThCr₂Si₂-type quaternary chalcogenides as efficient Pt-free counter electrodes for dye-sensitized solar cells

Two quaternary chalcogenides of ThCr₂Si₂-type K₂FeCu₃Q₄ (Q for S and Se) were utilized as new type of Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The X-ray photoelectron spectroscopy (XPS), Mott−Schottky analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to clarify the differences in energy band alignments, electrocatalytic and photovoltaic performances. A photoelectric conversion efficiency (PCE) of 5.07% was achieved in DSSCs assembled with K₂FeCu₃Se₄ CE, which was obviously superior to that of K₂FeCu₃S₄ CE (3.42%) and comparable with that of Pt CE (6.25%) under one sun AM 1.5 G illumination (100 mW cm⁻²). Compared to K₂FeCu₃S₄ CE, the higher PCE of K₂FeCu₃Se₄ CE can be attributed to the better catalytic activity for I₃⁻ reduction, stronger driving force for electron injection from CE to electrolyte, faster electron transfer and electrolyte diffusion channels.