Of late, inorganic perovskite material, especially the lead-free CsGeBr3, has gained considerable interest in the green photovoltaic industry due to its outstanding optoelectronic, thermal, and elastic properties. In this work, we systematically investigated the strain-driven optical, electronic, and mechanical properties of CsGeBr3 through the first-principles density functional theory. The unstrained planar CsGeBr3 compound demonstrates a direct bandgap of 0.92 eV at its R-point. However, by incorporating external biaxial tensile (compressive) strain the bandgap lowering (increasing) can be tuned to this perovskite. Moreover, due to the increase of tensile (compressive) strain, a red-shift (blue-shift) behavior of the absorption-coefficient and dielectric function is found in the photon energy spectrum. Strain-induced mechanical properties also reveal that CsGeBr3 perovskites are mechanically stable and highly ductile material and can be made suitable for photovoltaic applications. The strain-dependent optoelectronic and mechanical behaviors of CsGeBr3 explored here would be beneficial for its future applications in optoelectronics and photovoltaic cells design.

Halide perovskites are promising photovoltaic, solar cell, and semiconductor materials. Density-functional theory (DFT) models address compressive and tensile biaxial strain effects on APbCl3, where A = (K, Rb, and Cs). This research shows how A-cation impacts bandgap energy and band structure. The direct bandgap for KPbCl3, RbPbCl3, and CsPbCl3 is found 1.612, 1.756, and 2.046 eV, respectively; increases from A=K to Cs. When spin-orbital coupling (SOC) is introduced, bandgaps in KPbCl3, RbPbCl3, and CsPbCl3 perovskites are reduced to 0.356, 0.512, and 0.773 eV, respectively. More tensile strain widens the bandgap; compressive strain narrows it. Without SOC, the bandgaps of KPbCl3, RbPbCl3, and CsPbCl3 were tuned from 0.486 to 2.213 eV, 0.778 to 2.289 eV, and 1.168 to 2.432 eV, respectively. When the compressive strain is increased, the dielectric constant of APbCl3 decreases (red shift) and increases (blue shift) as the tensile strain is increased. Strain improves APbCl3 perovskite's optical performance.

The photocatalytic characteristics of two-dimensional (2D) GeC-based van der Waals heterobilayers (vdW-HBL) are systematically investigated to determine the amount of hydrogen (H2) fuel generated by water splitting. We propose several vdW-HBL structures consisting of 2D-GeC and 2D-SiC with exceptional and tunable optoelectronic properties. The structures exhibit a negative interlayer binding energy and non-negative phonon frequencies, showing that the structures are dynamically stable. The electronic properties of the HBLs depend on the stacking configuration, where the HBLs exhibit direct bandgap values of 1.978 eV, 2.278 eV, and 2.686 eV. The measured absorption coefficients for the HBLs are over ~ 105 cm−1, surpassing the prevalent conversion efficiency of optoelectronic materials. In the absence of external strain, the absorption coefficient for the HBLs reaches around 1 × 106 cm−1. With applied strain, absorption peaks are increased to ~ 3.5 times greater in value than the unstrained HBLs. Furthermore, the HBLs exhibit dynamically controllable bandgaps via the application of biaxial strain. A decrease in the bandgap occurs for both the HBLs when applied biaxial strain changes from the compressive to tensile strain. For + 4% tensile strain, the structure I become unsuitable for photocatalytic water splitting. However, in the biaxial strain range of − 6% to + 6%, both structure II and structure III have a sufficiently higher kinetic potential for demonstrating photocatalytic water-splitting activity in the region of UV to the visible in the light spectrum. These promising properties obtained for the GeC/SiC vdW heterobilayers suggest an application of the structures could boost H2 fuel production via water splitting.

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