Dye-sensitized solar cells (DSSCs) have attracted great attention as one of next-generation photovoltaic devices due to low cost and simple fabrication process. A conventional DSSC consists of TiO₂ photoelectrode, counter electrode (CE) and liquid electrolytes containing iodide/triiodide (I/I₃^-) redox couple sandwiched between the electrodes. The CE serves to collect electrons and catalyze redox couple regeneration; thus, its material and performance determine the cost and photoelectric conversion efficiency of DSSC. Generally, noble Pt is employed as a CE owing to its rapid electron transfer ability and superior electrocatalytic behavior toward I₃^- species. However, Pt is expensive and limited in resource. Hence, it is vital to find inexpensive and readily available non-Pt catalysts for the development of DSSCs.

Carbon materials, conductive polymers, transition-metal compounds, metal alloys, and their composites have been explored to replace Pt. Among these alternatives, transition-metal compounds including carbides, nitrides, chalcogenides and oxides have demonstrated some desirable performances. MoS₂ consists of three atom layers: one Mo layer sandwiched between two S layers via weak Vander Waals interactions. Advantageously, MoS₂ has abundant exposed active sulfur edges for catalytic activity. On the other hand, graphitic carbon nitride (g-C₃N₄) demonstrates excellent thermal and chemical stability as well as interesting electric properties, which make it have good catalytic activity for a variety of reactions. In addition, g-C₃N₄ can be economically prepared in large scale. Herein, we present the fabrication and characterization of porous g-C₃N₄ nanosheet/MoS₂ nanoparticle (g-C₃N₄/MoS₂) composite. Such an architecture can provide short diffusion distance for excellent charge transport as well as large contact area for fast interfacial charge separation and electrochemical reactions. As a result, the nanocomposite is anticipated to exhibit good electrochemical and catalytic activities.

In this study, we first developed a solution-based coating method to prepare g-C₃N₄/MoS₂ counter electrode. Through a facile hydrophilization process for g-C₃N₄ and sintering the Mo-S precursor coated g-C₃N₄ at 280 °C for 12 h, crystalline MoS₂ nanoparticles were formed on g-C₃N₄ substrate, resulting in strong mechanical adhesion. In addition, low-cost solution-processed g-C₃N₄/MoS₂ electrode had similar electrocatalytic behavior toward I₃^- species to Pt. As a result, the DSSC based on g-C₃N₄/MoS₂ demonstrates desirable photovoltaic performance.