Fe Single Atom Catalysts Promoting Polysulfide Redox Reduction in Quantum Dot Photovoltaics

Developing cost-effective and highly efficient photocathodes toward polysulfide redox reduction is highly desirable for advanced quantum dot (QD) photovoltaics. Herein, we demonstrate nitrogen doped carbon (N-C) shell-supported iron single atom catalysts (Fe-SACs) capable of catalyzing polysulfide reduction in QD photovoltaics for the first time. Specifically, Fe-SACs with FeN₄ active sites feature a power conversion efficiency of 13.7% for ZnCuInSe-QD photovoltaics (AM1.5G, 100 mW/cm²), which is the highest value for ZnCuInSe QD-based photovoltaics, outperforming those of Cu-SACs and N-C catalysts. Compared with N-C, Fe-SACs exhibit suitable energy level matching with polysulfide redox couples, revealed by the Kelvin probe force microscope, which accelerates the charge transferring at the interfaces of catalyst/polysulfide redox couple. Density functional theory calculations demonstrate that the outstanding catalytic activity of Fe-SACs originates from the preferable adsorption of S₄^2– on the FeN₄ active sites and the high activation degree of the S–S bonds in S₄^2– initiated by the FeN₄ active sites.