Computational modeling of two - dimensional heterostructures for optoelectronic and catalytic applications

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PhD; 2023; Materials research centre

Two-dimensional van der Waals (2D-vdW) materials have attracted significant attention for their unique and excellent properties. The properties of the 2D-vdW materials can be precisely engineered using various techniques for the desired applications. We carried out a study of 2D-vdW materials and their heterostructures for optoelectronic and catalytic applications using state of the art ab-initio modeling such as density functional theory (DFT), many-body perturbation theory (MBPT), and density functional perturbation theory (DFPT). We report the generation of linearly polarized, anisotropic, intra and interlayer excitonic bound states in GeSe/SnS vdW heterostructure using GW and Bethe-Salpeter equation simulations (BSE), addressing the current demand of optical polarizers. A dramatic variation in excitonic binding energy and optical band gap is observed upon applying biaxial strain, which is attributed to the change in effective dielectric constant and band dispersion. Building upon the concept of optical and excitonic properties, we discuss the Z-scheme mechanism in C3N3/C3N4 vdW heterostructure for water splitting catalysts. The spontaneous redox reactions for the water splitting combined with band alignment, presence of higher-order interlayer excitons, fast electron-hole recombination, and high charge mobility facilitate the Z-scheme mechanism compared to the type II mechanism. For optoelectronic applications, the stacking order plays a crucial role in 2D materials. Rhenium disulfide (ReS2) is one of the most potential candidates for optoelectronic properties; however, extremely weak interlayer coupling strength makes it challenging to determine the stacking order in multilayer ReS2. We successfully identify two distinct stacking orders (AA & AB) by the potential energy profile and the vibrational Raman modes. We extend this study to determine the stacking-order-driven optical and excitonic properties. By symmetry analysis, we also explore the origin of extra Raman modes and splitting of Raman modes in multilayer ReS2, which is another debatable topic. The extra modes and the splitting in Raman spectra are attributed to the layer parity-dependent breaking of inversion symmetry. Due to the weak coupling strength between the layers, multilayer ReS2 is designed with a proper doping strategy for the layer-independent deep center defects. The thermodynamic study confirms that S_Re is the best possible deep isolated defect for a single photon emitter. This study highlights the importance of hetero structuring, stacking-order, and strain engineering to study the extraordinary properties of 2D materials and also paves the path to overcome critical challenges in optoelectronic research applications.