Tailoring the work function of SnS₂/SnO₂ composites for improved counter electrode performance in dye-sensitized solar cells

Tuning the work function of counter electrode (CE) materials is a novel strategy to improve the catalytic activity of I-/I-3(-) electrolyte reduction, thereby improving the performance of dye-sensitized solar cells (DSSCs). To this aim, we prepared pristine SnS2 and SnS2/SnO2 composites (with 3, 5, 7, and 10 wt.% of SnO2) through the hydrothermal method and examined their CE performance in DSSCs. Indeed, the BET analysis confirms that 5 wt.% SnS2/SnO2 composites (SS-5) have large surface area (195.565 m(2)/g) when compared to pristine SnS2 (188.749 m(2)/g) and consequently have less charge transfer resistance. Also, the redox peak-to-peak separation is found to be minimum in SS-5 composite (0.16 V), indicating its excellent catalytic activity. Importantly, the Kelvin-probe force microscopic (KPFM) analysis reveals that the work function of the SS-5 (4.54 eV) has decreased reasonably compared to that of pure SnS2 (4.79 eV) and favors the efficient charge transfer between CE and electrolyte. Consequently, the DSSCs fabricated with SS-5 CE exhibit a better power conversion efficiency (PCE) of 5.1% which is more than that of platinum CE (i.e., 5.0%). The mechanism behind the improved performance has been studied extensively and the reported work commences a simple approach to develop cost-effective Pt-free CE.