Fabrication And Investigation Of The Optoelectrical Properties Of MoS₂ Nanofilms

Two-dimensional（2D） nanomaterials have received much attention, due to their exceptional properties, ultra-thin thickness, and 2D morphology. Besides grapheme which has raised great research interest, other types of 2D nanomaterials such as metal dichalcogenides have also been widely studied and employed in many fields, such as electronics, photovoltaic devices, and so on. Molybdenum disulfide（MoS₂） has become widely studied semiconductor material because of its hexagonal crystalline structure, large bandgap, excellent electrical and optical properties, and the absence of dangling bonds. It has been widely applied in many areas, like field effect transistors, organic light-emitting diode, counter electrode and cocatalyst. In this paper, we explored the optimum conditions of preparing MoS₂ thin film using chemical vapor deposition（CVD）, and studied the structures and properties of the field effect transistors and solar cells based on MoS₂ thin films.The MoS₂ thin films were fabricated on the Si substrates via CVD using the saturated MoS₂ solution and argon（Ar） gas as raw material and carrier gas, respectively. And the surface morphologies, structures, electrical properties and optical properties of MoS₂ film samples with different deposition temperatures, deposition times and annealing temperatures were characterized by scanning electron microscopy, metallographic microscope, X-ray diffraction, UV-3600 spectrophotometer and Hall Effect Measurement System. Finally, the optimum conditions that deposition temperature, deposition time and annealing temperature were 550 °C, 20 min and 850 °C, respectively were obtained.Then back-gated field effect transistors with Ni as contact electrodes were fabricated on the Si/SiO₂ substrates via CVD. The related properties of MoS₂ thin films and the electrical properties of the prepared MoS₂ field effect transistors were studied systematically. The transistors have good transfer characteristics and output characteristics, with an on/off current ratio of up to 1.9 × 105, a maximum transconductance of approximately 5.4 μS/μm, and a mobility as high as 368 cm2/（Vs）, which indicates that the MoS₂ transistors can be easily modulated by the back gate.Finally, MoS₂/CdS heterojunction solar cells were synthesized on the conductive glass substrates via chemical bath deposition（CBD） and chemical vapor deposition. And the morphologies, the structures, the optical absorption properties and the electrical properties of MoS₂ and CdS thin films, and the optoelectrical properties of MoS₂/CdS heterojunction solar cells were studied systematically. MoS₂ and CdS thin films have good crystal structures and electrical properties. The optical absorption range of the MoS₂/CdS heterojunction solar cell covers the wavelength region of 350-800 nm, which is beneficial for the improvement of the efficiency of solar cells. Moreover, the MoS₂/Cd S solar cells have good rectification characteristics and pronounced photovoltaic behavior, with an open-circuit voltage of 0.66 V, a short-circuit current of 0.136 μA, comparable to the results achieved in other Mo S₂-based solar cells.