**6. Optoelectronic applications**

2D materials have interesting properties for photonics and optoelectronics compared with other materials. 2D materials enables charge carrier generation by light absorption over a very wide energy spectrum including the ultraviolet, visible, short‐wave infrared (SWIR), near‐ infrared (NIR), mid‐infrared (MIR), far‐infrared (FIR), and terahertz (THz) spectral regimes [7]. Moreover, 2D materials have ultrafast carrier dynamics, wavelength‐independent absorption, tunable optical properties via electrostatic doping, low dissipation rates and high mobility, and ability to confine electromagnetic energy in small volumes [3]. Electrons in 2D crystals possess a valley degree of freedom (DOF) in addition to charge and spin [67]. 2D materials exhibit an anomalous Hall effect whose sign depends on the valley index effect (VHE). It implies that circularly polarized light excites electrons into a specific valley in the structure band, causing a finite anomalous Hall voltage whose sign is controlled by the helicity of the light [67]. The electronic structure changes at the edges of the 2D crystalline structure of MoS2 resulting in strong resonant nonlinear optical susceptibilities due to the translational symmetry breaking [68]. Graphene layers are used as electrodes with tunable work function, while TMDs are applied as photoactive material due to the strong light‐matter interaction and photon absorption. TMDs exhibit transparency, mechanical flexibility, and easy processing [7]. Also, they have the ability to tune the optical band gap by varying the number of monolayers to allow the detection and emission of light (electroluminescence) at different wavelengths. 2D materials present the photovoltaic effect, the photo‐thermoelectric effect, the bolometric effect, the photogating effect and the plasma‐wave‐assisted mechanism [3, 69]. Applications such as transparent electrodes in displays, photovoltaic modules, photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have been developed [7]. 2D TMDs exploit their primary figure of merit and low room‐temperature photoluminescence quantum yield (QY) for applications such as light‐emitting diodes, lasers, and solar cells based on MoS2 [70].
