MoS₂ coated CoS₂ nanocomposites as counter electrodes in Pt-free dye-sensitized solar cells

Expensive Pt counter electrodes remain an obstacle for the commercialization of dye-sensitized solar cells (DSSCs). Therefore, research focusing on low-cost alternative counter electrode materials has been considered important for their commercialization. Here, the fabrication of dye-sensitized solar cells has been performed utilizing CoS₂ and MoS₂ coated CoS₂ nanocomposite materials as the counter electrode, which are synthesized via a hydrothermal route involving low-cost precursor materials. The experimental results obtained from XRD, XPS, EDX, SEM, TEM, and Raman etc. have confirmed the successful formation of CoS₂ and MoS₂ coated CoS₂ nanocomposites. The electrochemical characterization of these materials is performed, which suggests that the electrocatalytic activity towards the liquid iodine electrolyte of these materials is as good as that of the conventional Pt counter electrodes. So, dye-sensitized solar cell devices are fabricated by interpolating a (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii)) dye-loaded TiO₂ photoanode and CoS₂, MoS₂ coated CoS₂ and Pt counter electrodes using iodine/iodide as a liquid electrolyte. The devices fabricated with CoS₂ counter electrodes have shown an open circuit voltage of 790 mV, a short circuit current of 11.9 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6%. On the other hand, the device based on a Pt counter electrode has shown an open circuit voltage of 773 mV, a short circuit current of 13.4 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6.6%. In addition, MoS₂ coated with a CoS₂ counter electrode has shown the best performance with an open circuit voltage of 763 mV, a short circuit current of 20.1 mA cm^-2, a fill factor of 0.42, and a power conversion efficiency of 7.6%.