Salt-Assisted High-Throughput Synthesis of Single- and Few-Layer Transition Metal Dichalcogenides and Their Application in Organic Solar Cells

A modified liquid-phase ultrasonication method, namely 'salt-assisted liquid-phase exfoliation' is studied, which yields single- and few-layer transition metal dichalcogenides (TMD) 2D sheets including in a large quantity and high quality by simple ultrasonication of TMD bulk crystals in liquid solvents with the aid of low-cost and non-toxic inorganic salts. In this salt-assisted synthesis, powders of TMD crystals are immersed in an inorganic salt containing aqueous solution, and salt ions are allowed to enter into the inter-layer spaces of TMD crystals as the solution becomes supersaturate upon water evaporation. This intermediate product is then exfoliated easily into corresponding single- and few layer 2D sheets by low power ultrasonication in an organic solvent. As proof-of-concept, solution casted thin films of MoS₂ 2D sheets were integrated into organic solar cells (OSCs) to serve as the HTL, which shows a remarkable improvement of the V_oc from 0.34 V to 0.58 V. Because the synthesis does not require any hazardous chemicals, electrochemical setup, or special reaction chamber, the salt-assisted strategy is very promising to scale up for mass production in the future.