High performance electrocatalyst consisting of CoS nanoparticles on an organized mesoporous SnO₂ film: Its use as a counter electrode for Pt-free, dye-sensitized solar cells

High energy conversion efficiencies of 6.6% and 7.5% are demonstrated in solid and liquid states, Pt-free, dye-sensitized solar cells (DSSCs), respectively, based on CoS nanoparticles on an organized mesoporous SnO₂ (om-SnO₂) counter electrode. These results correspond to improvements of 14% and 9%, respectively, compared to a conventional Pt counter electrode and are among the highest values reported for Pt-free DSSCs. The om-SnO₂ layer plays a pivotal role as a platform to deposit a large amount of highly electrocatalytically active CoS nanoparticles via a facile solvothermal reaction. The om-SnO₂ platform with a high porosity, larger pores, and good interconnectivity is derived from a poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer template, which provides not only improved interaction sites for the formation of CoS nanoparticles but also enhanced electron transport. The structural, morphological, chemical, and electrochemical properties of CoS on the om-SnO₂ platform are investigated using field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) measurements. The performance enhancement results from the excellent electron transport at the fluorine-doped tin oxide (FTO)/counter electrode/electrolyte interface, reduced resistance at the FTO/CoS interface, and better catalytic reduction at the counter electrode/electrolyte interface.