Thickness controlling bandgap energy, refractive index and electrical conduction mechanism of 2D Tungsten Diselenide (WSe2) thin films for photovoltaic applications

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2022-02, Vol.128 (2), Article 94
• Main Authors: Alzaid, Meshal, Hadia, N. M. A., Shaaban, E. R., El-Hagary, M., Mohamed, W. S.
• Format: Article
• Language: English
• Subjects: Absorptivity; Applied physics; Characterization and Evaluation of Materials; Condensed Matter Physics; Crystallites; Crystallization; Dispersion curve analysis; Electrical conduction; Electron beams; Energy gap; Film thickness; Glass substrates; Grain boundaries; Hopping conduction; Machines; Manufacturing; Materials science; Microstrain; Morphology; Nanotechnology; Optical and Electronic Materials; Photovoltaic cells; Physics; Physics and Astronomy; Processes; Refractivity; Room temperature; Selenides; Spectroellipsometry; Surfaces and Interfaces; Thin Films; Tungsten compounds
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-021-05188-z

This paper reports thickness-dependent structural, morphological, optical, and electrical conduction mechanism of room temperature electron beam evaporated 2D WSe 2 thin films on glass substrate. The thickness of the WSe 2 films was varied from 100 to 400 nm. XRD results showed the fact that the WSe 2 films are crystallized in a hexagonal structure. The nanostructure nature is verified from morphological studies. It was found that the microstrain decreases, while the crystallite size rises as the thickness of WSe 2 film increases. The thickness-dependent optical constants and energy bandgap was studied using spectroscopic ellipsometry (SE). The refractive index and extinction coefficient dispersion curves of WSe 2 film with various thicknesses display two strong absorption peaks A and B below 800 nm at 580 nm and 770 nm, which are belong to excitonic absorption features. Further, the results illustrate that the optical constants and optical bandgap of thin WSe 2 films are strongly correlated with the film thickness. In addition, the electrical conduction mechanism in different temperature regimes is explained in terms of Arrhenius activated thermal conduction, Mott's variable-range hopping (VRH), and Seto's grain boundary effect models. The most interesting finding is that the film exhibits wide absorption coefficient (10 6  cm −1 ) and energy gap value closely matches the solar spectrum, making it an excellent candidate for photovoltaic materials as an absorber layer.