A scalable, solution-based approach to tuning the solubility and improving the photoluminescence of chemically exfoliated MoS₂

MoS₂ are two-dimensional (2D) materials that exhibit emerging photoluminescence (PL) at the monolayer level and have potential optoelectronic applications. Monolayers of MoS₂ typically achieved by mechanical exfoliation (Me), chemical vapor deposition (CVD), and chemical exfoliation (Ce) via lithium intercalation contain numerous defects that significantly reduce their PL efficiency. Several studies have reported overcoming poor PL in mechanically exfoliated and CVD-grown MoS₂, but such studies for chemically exfoliated MoS₂ (Ce-MoS₂) have not been reported. Here, we report a solution-based method of enhancing the PL of Ce-MoS₂ by reacting with molecules with suitable functional groups at high temperatures. Reaction with dodecanethiol (DDT) generates PL that is more intense than mechanically exfoliated MoS₂ (Me-MoS₂) with high crystallinity and has a significantly broader range of wavelengths. Based on ultraviolet-visible, Fourier transform infrared, X-ray photoemission, and PL spectroscopy as well as transmission electron and PL imaging, we propose that the present method modifies PL properties of Ce-MoS₂ by simultaneously annealing, replacing molybdenum-oxygen with molybdenum-sulfur bonds, inducing strain, and generating a nanopolycrystalline structure. This work points to such defect engineering using molecules as an effective means to modify the properties of Ce-MoS₂ and layered transition-metal dichalcogenides more generally.