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By means of the study of the first principles within the framework of density functional theory, the inorganic metal halide perovskite CsGeX3 (X = Cl, Br, and I) is thoroughly investigated for its potential application in the field of green energy harvest. The structural, electronic, optical, mechanical, and piezoelectric properties have been calculated. Herein, the computed electronic properties reveal a direct bandgap semiconducting nature with electronic bandgap Eg$_{\text{g}}$ = 2.01, 1.38, and 0.85 eV for X = Cl, Br, and I, respectively. Since the most prominent absorption peak falls within the vis–UV region, this implies that they are the potential candidates for photovoltaic applications. To check and verify the thermal stability, the MD simulation was performed with time steps up to 5 ps. The highest piezoelectric coefficient values are 0.731, 1.829, and 12.48 C m−2 for X = Cl, Br, and I, respectively. The higher piezoelectric responses indicate the signature of the efficient energy materials for energy harvest through electromechanical processes. [ABSTRACT FROM AUTHOR]

Structural, electronic and optical properties of strained CdS monolayer and bilayer structures are studied to examine the possibility of controlling their properties for application in the field of nano-devices. First-principles density functional theory (DFT) calculations are done as implemented in SIESTA code that uses a pseudopotential and a numerical nano-orbital basis set. Exchange correlation energies were described using the general gradient approximation (GGA) in the form of Perdew–Burke–Ernzerhof (PBE) functional. We have found that the electronic band structure of monolayer and bilayer CdS is quite sensitive to biaxial strain, and as a result bandgap energy can be tuned over a wide range with compressive and tensile strains. While both the monolayer and bilayer structures maintain the direct bandgap nature of the relaxed structure even under compressive strain, tensile strain transforms the material into indirect gap semiconductors with degenerate electronic band structure. It is found that effective masses can also be controlled with biaxial strain, and hence carrier mobility can be improved in the process. Our DFT calculations also predict that in addition to tuning the optical absorption, intensity of direct bandgap absorption in these two structures can be enhanced under tensile strain. [ABSTRACT FROM AUTHOR]