Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as a new generation of semiconducting materials for electronic and optoelectronic applications. Despite their extraordinary application potential, challenges persist in harnessing their full capabilities. 2D TMDs are predisposed to form atomic defects, such as chalcogenide vacancies, that cause charge carrier trapping in defect-induced potentials and result in non-radiative recombination pathways, thereby reducing charge carrier mobility. Additionally, the strong electrostatic interactions in 2D TMDs enable the formation of trions, quasiparticles composed of an exciton and free charges, even at room temperature. The existence of trions and defects strongly influence the intrinsic optical and electronic properties of TMDs. Despite extensive research focused on improving the semiconducting quality of 2D TMDs, the challenge remains in mitigating the defects within these materials. Photoluminescence (PL) intensity and charge carrier mobility (μ) are key indicators of the quality of 2D TMDs for optoelectronic applications, as they are sensitive to traps, structural defects, and charged impurities. Among various approaches, surface chemical strategies stand out as versatile and non-destructive methods to enhance the properties of 2D TMDs. In spite of advances in materials growth in recent years, our understating of defects, particularly the interaction of defects with passivating chemicals remains unclear. Even the widely discussed treatment with organic super-acid H-TFSI results in trap-limited PL and potentially damages TMD materials and contacts, limiting its application in devices. Although the benign chemical treatment based on Li-TFSI has led to a PL increase twice that of the H-TFSI, it does not lead to electrical mobility improvement. Consequently, no chemical treatment has yet been able to significantly enhance both the PL and electrical mobility of 2D TMDs.