Earth Abundant Silicon Composites as the Electrocatalytic Counter Electrodes for Dye-Sensitized Solar Cells

Earth abundant silicon compounds, including Si₃N₄, SiO₂, SiS₂, and SiSe₂, were introduced as the electrocatalytic materials for the counter electrodes (CE) in dye-sensitized solar cells (DSSCs). Among these silicon-based materials, Si₃N₄, SiS₂, and SiSe₂ were applied in DSSCs for the first time. In the presence of a conducting binder, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), various silicon-based composites (Si₃N₄/PEDOT:PSS, SiO₂/PEDOT:PSS, SiS₂/PEDOT:PSS, and SiSe₂/PEDOT:PSS) were successfully coated on the ITO substrates via a simple drop-coating process. In a composite film, silicon-based nanoparticles provided attractive electrocatalytic ability and plenty of electrocatalytic active sites for the triiodine ion (I₃^-) reduction. PEDOT:PSS not only acted as a good conducting binder for silicon-based nanoparticles, but also provided a continuous polymer matrix to increase the electron transfer pathways. By adjusting the weight percent (1-5 wt %) of the silicon-based nanoparticles (Si₃N₄, SiO₂, SiS₂, and SiSe₂) with respect to the weight of PEDOT:PSS, the composite films containing 5 wt % Si₃N₄ (denoted as Si₃N₄-5) and 5 wt % SiSe₂ (denoted as SiSe₂-5) both reached excellent electrocatalytic abilities and rendered the good cell efficiencies (η) of 8.2% to their DSSCs. It can be said that both Si₃N₄-5 and SiSe₂-5 are promising electrocatalytic materials to replace the rare and expensive Pt (η = 8.5%).