Tri-iodide Reduction Activity of Shape- and Composition-Controlled PtFe Nanostructures as Counter Electrodes in Dye-Sensitized Solar Cells

PtFe alloy nanostructures enclosed by differently oriented facets, including polyhedrons, concave cubes, and nanocubes, were synthesized through the fine adjustment of specific surfactant-crystal facet bindings. PtFe nanostructures with various alloy compositions were then employed as the counter electrodes (CEs) for the redox reaction of iodide/tri-iodide (I-/I-3(-)) in dye-sensitized solar cells. Devices with the Pt9Fe1 polyhedrons and Pt9Fe1 concave cubes produced better photovoltaic conversion efficiency (PCE) of 8.01% and 7.63% in comparison to the PCE of 7.24% achieved with Pt CE. The superiority is attributed to the rapid charge transfer, higher limit current, and better electronic conductivity and catalytic activity with respect to the Pt CEs. The photovoltaic and electrochemical results indicated the shape- and composition-dependent activity in the I-/I-3(-) redox reaction, which obeys the sequence of polyhedrons > concave cubes > nanocubes and Pt9Fe1 nanostructures > Pt7Fe3 nanostructures. Further theoretical work indicated that the I-3(-) reduction activity of the nanosurfaces was in the order of Pt9Fe1 (111) > Pt(111) > Pt9Fe1 (100). The combination of experimental and theoretical work thus clearly demonstrates the shape- and composition-dependence of PtFe nanostructures in terms of the I-3(-) reduction activity.