Two-Dimensional Molybdenum Disulfide Nanosheets Based Optoelectronic Devices

In recent times, nanosheets of two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been extensively used in various optoelectronic applications due to their intriguing optical and electronic properties. These TMDCs are composed of transition metal and chalcogen elements (sulfur, selenium, or tellurium). There are various TMDCs nanosheets which have been synthesized and their properties have been explored, viz. molybdenum disulfide (MoS2), tungsten disulfide (WS2), etc. Here, in this chapter, we shall be considering MoS2, and its various properties and optoelectronic applications in devices, such as photodetector, photovoltaic, light emitting diodes, etc. Being a good semiconducting material, MoS2 shows high electrical conductivity, high carrier charge concentration, and higher current on/off ratio. Monolayer MoS2 sheet is made up of molybdenum (Mo) atoms of hexagonal lattice sandwiched inbetween two similar sulfur (S) atoms lattices in a trigonal prismatic arrangement. The MoS2 has a tunable bandgap, it exhibits strong interaction with photons, and the nanosheets can be combined with other 2D nanosheets to form heterostructures, which have plausible applications in flexible optoelectronic devices. Bulk MoS2 shows 1.2 eV of indirect band gap, while 1.9 eV of direct band gap is exhibited by mono-layered MoS2 sheet. Number of layers of the MoS2 sheet strongly influence the electrical and optical properties of MoS2. These nanosheets can also be incorporated with other nanomaterials to enhance the device efficiency by synergistic effect. In this chapter, we shall cover a few recent developments regarding optoelectronic devices based on MoS2 nanosheets along with various methods of synthesizing MoS2 nanosheets and fabricating optoelectronic devices.