Center for Materials Engineering

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Browsing Center for Materials Engineering by Subject "band alignment"

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    First Principles Investigation of Van Der Waals Heterostructures of Mos2 and Janus Transition Metal Dichalcogenides for Energy Applications
    (Addis Ababa University, 2021-09) Birhan, Tesfaye; Georgies, Alene (PhD)
    Recent research on the Janus transition metal dichalcogenide (JTMD) with an asymmetric structure has revealed that this material possesses interesting unique properties, notably in solar cells. This work is based on cutting-edge density functional theory (DFT) computations utilizing Generalized Gradient Approximation- Perdew–Burke–Ernzerhof functional (GGA-PBE) as implemented in the Quantum ESPRESSO and VASP codes. To find the most stable optimized heterostructures, eight basic stacking patterns were designed. Then, for MoSSe/MoS2, WSSe/MoS2, and MoSTe/MoS2 heterobilayer, the AAII-S stacking mode was more stable than the other stacking types. According to the findings, the band alignment was type-I for MoSSe/MoS2, MoSTe/MoS2, and type-II for WSSe/MoS2, within, 1.03, 0.30 and 0.84 eV are estimated bandgap, respectively. The electrical band structure, as well as band edge placements, was investigated. When the water redox and oxidation potentials of heterostructures were compared, it was discovered that MoSSe/MoS2, MoSTe/MoS2, and WSSe/MoS2 were not applicable for photocatalytic materials for full water splitting. On the other hand, MoSSe/MoS2 and MoSTe/MoS2 heterostructures were placed lower than the oxidation potential of O2/H2O, making them applicable for oxygen evolution reaction (OER). This work reveals that JTMDs/MoS2 heterostructures are often subsequent material that promotes the development of photovoltaic devices, specially MoSSe/MoS2, and WSSe/MoS2 vdWH. The power conversion efficiency (PCE) of the heterostructures is calculated, and the results show that MoSSe/MoS2 and WSSe/MoS2 show very good efficiency with values of 19.41% and 16.25%, respectively. The result is good when compared to other similar studies: GaTe-InSe (9.1%), MoS2/p-Si (5.23%), organic solar cells (11.7%), and PN-WSe2 (13.8 % ). Since the results are encouraging, we believe it is a good idea to do additional experiments on the heterostructures and adapt them to solar cell applications.
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    First-Principles Study Of Van Der Waals Heterostructures of MoSeTe/ZnO for Investigating Photocatalytic Water-Splitting and Photovoltaic Applications
    (Addis Ababa University, 2023-06) Derese, Abraham; Georgies, Alene (PhD)
    Two-dimensional (2D) heterostructures have allowed for the development of novel properties with interesting applications in photocatalytic water splitting and optoelectronic devices. Electronic properties of ZnO and Janus MoSeTe monolayers were investigated using density functional theory (DFT)-based first-principles calculations, and depending on the lattice mismatch, layered 2D MoSeTe/ZnO heterostructures were produced. In this study, the first-principles van der Waals corrected density functional theory calculations were also performed on ABI_Se, ABI_Te, and ABII_Te heterostructure.Out of eight basic stacking patterns of the ZnO/MoSeTe hetero-bilayer designed, the ABII-Te stacking mode was a more stable stacking type due to the small lattice mismatch and the binding energy. The result showed that the band alignment for ABI_Se, ABI_Te, and ABII_Te was done on the electrical band structure and band edge positions, and confirmed type two band alignment. In addition, the ABI_Se, ABI_Te, and ABII_Te configurations of ZnO/MoSeTe vdW heterostructures are indirect band gap semiconductors. The investigated 2D ZnO/MoSeTe heterostructures have an acceptable band gap for solar applications, according to a first-principles study. The power conversion efficiency of ZnO/MoSeTe heterostructure is computed, and the results exhibit ABI_Se, ABI_Te, and ABII_Te stacking orientations have high efficiency with values of 22.26%, 22.31%and22.17%, respectively. Therefore, our findings show the heterostructures have reasonable band gaps and high PCE, and exhibit type-II band alignment, which are suitable candidates for solar cell application. Furthermore, for full water splitting heterostructures cannot satisfy the band edge requirements; however, the heterostructures are a good photocatalyst for the hydrogen evolution reaction. The heterostructure's ability to split water more effectively can be improved by moving the band edges position using strain and doping.