Intrinsic Origin of Superior Catalytic Properties of Tungsten-based Catalysts in Dye-sensitized Solar Cells

Abstract To clarify the intrinsic factor of the superior catalytic activity of tungsten (W)-based catalysts in DSSCs, W-based compounds, including W 18 O 49 , W 2 N, WC, and WO 3 , were prepared as CEs and tested in I − /I 3 − redox shuttle. A systematic investigation of the catalytic properties and stability, as well as first-principle density functional theory (DFT) calculations, was performed for these W-based catalysts in DSSCs. The DSSCs assembled with the I − /I 3 − redox shuttle, based on W 18 O 49 , W 2 N, WC, and WO 3 CEs, exhibited power conversion efficiencies (PCEs) of 6.69%, 5.97% 5.20%, and 4.69%, respectively; these values were equal to or better than those of DSSCs with Pt CEs (6.52%) under the same conditions. The superior electrocatalytic activities of W-based compounds are determined by their electronic structure. Electronic density of states (DOS) revealed that the band gaps of W 18 O 49 , W 2 N, WC, and Pt were zero, whereas that of WO 3 was 1.7 eV. Wider band gaps do not facilitate electron conduction as easily as Pt. In addition, the W/O ratio (1:2.72) in W 18 O 49 was greater than that in WO 3 (1:3), and the W/N ratio (2:1) in W 2 N was greater than that in WC (1:1). Higher ratios of W/(O or N) favored the electrocatalytic activity of the CE materials in the reduction of I 3 − in DSSCs. This is the intrinsic reason why W-based compounds exhibit different catalytic properties in DSSCs under the same conditions. This work sheds light on the origin of W-based catalysts, and explains the differences in the catalytic performances of W-based compounds for this work and several published works.