Lead-free cubic CsXF3 (X = Sn, Ge, Zn, Sr) fluoride perovskites are promising, environmentally friendly candidates for sustainable optoelectronic technologies. In this work, their structural, energetic, lattice dynamical, and broadband optical properties are systematically investigated using density functional theory (DFT). Comparative functional assessments demonstrate that the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) method provides superior structural accuracy over PBE revised for solids (PBEsol) and successfully curbs the artificial atomic over-binding inherent to local density approximation (LDA). Total energy and Goldschmidt tolerance factor analyses confirm robust thermodynamic stability against decomposition. However, harmonic phonon dispersion calculations reveal critical dynamical instabilities within the ideal cubic lattice at 0 K for CsSnF3, CsGeF3, and CsSrF3 due to pronounced imaginary modes, whereas CsZnF3 exhibits near-complete dynamic stability. Beyond structural profiles, this research emphasizes how diverse electronic configurations customize each compound for targeted device architectures. Specifically, the direct bandgaps of CsSnF3 (1.74 eV) and CsGeF3 (2.04 eV), combined with high optical conductivity, position them as exceptional visible-light harvesting photovoltaic absorbers. Conversely, the wide transparency windows and localized wide-bandgap profiles of CsZnF3 (3.64 eV) and CsSrF3 (6.29 eV) optimize them for solar-blind photodetectors and deep-ultraviolet (UV) optical windows, respectively. Crucially, planar average charge density and electrostatic potential analyses reveal that lone-pair-driven strong internal electric fields tailor CsSnF3 and CsGeF3 for active ferroelectric applications, whereas the uniform ionic charge distribution of CsZnF3 and CsSrF3 favors their utilization as reliable gate insulators and energy storage capacitors. Finally, spin–orbit coupling (SOC) assessments confirm that relativistic effects are negligible. Ultimately, these theoretical insights establish critical microscopic design guidelines for fluoroperovskite-based energy technologies.
The morphological, structural, and optical characterization of the SnS thin film deposited by the ultrasonic spray pyrolysis (USP) method was carried out. Simple and inexpensive commercial ultrasonic nano-mist device was used to deposit SnS thin film. The solution procedure was developed to obtain highly oriented SnS thin film. The SnS thin film exhibited an orthorhombic crystal structure with a strong (111) preferred orientation. The crystallite size was calculated as 56 nm. A direct band gap of 1.21 eV was determined from the Tauc plot. Raman spectroscopy was performed to identify the phases present in the films. The FTO/TiO2/SnS/Au solar cells were fabricated. The ideality factor and saturation current of the device were calculated as 3.02 and 2.59 × 10−6 A, respectively. The series resistance of 370 Ω was obtained using Cheung’s method. The photovoltaic parameters of the champion cell with a power conversion efficiency (PCE) of 0.388% were found to be Jsc = 6.50 mA/cm2, Voc = 0.207 V, and FF = 28.9%. In addition, the photodiode performance of the cell was evaluated.
The structural, electronic, vibrational, optical, and thermodynamic properties of yttrium hydrogen chalcogenides (YHS, YHSe, and YHTe) are systematically investigated using first-principles density functional theory (DFT), with phonon and thermodynamic properties determined using Phonopy calculations. All compounds are dynamically stable, exhibiting progressive lattice expansion from YHS to YHTe due to increasing chalcogen atomic size. Additionally chalcogen substitution effectively tunes the electronic structure by modulating the band gap and density of states (DOS) through enhanced hybridization between Y-d and chalcogen-p orbitals. Spin–orbit coupling (SOC) introduces subtle yet non-negligible modifications, with stronger effects observed for heavier chalcogens Te-based systems. The band gaps show slight SOC-induced variations, changing from 1.6385 to 1.6472 eV for YHS, 1.5152 to 1.5172 eV for YHSe, and from 1.52 to 1.42 eV for YHTe, reflecting enhanced relativistic effects in Te-based systems. YHS and YHSe retain indirect band gaps semiconductor, whereas YHTe exhibits a robust direct band gap semiconductor. Phonon dispersion confirms dynamical stability and reveals systematic softening of vibrational modes from YHS to YHTe, attributed to increased atomic mass and reduced interatomic force constants. This behavior correlates with enhanced electronic polarizability and modified bonding. Optical properties exhibit a red shift in the absorption edge with increased dielectric response. Thermodynamic analysis shows that entropy and specific heat increase with temperature, while Helmholtz free energy decreases and becomes more negative from YHS to YHTe, indicating improved thermodynamic stability. These findings highlight yttrium hydrogen chalcogenide compounds as promising tunable materials for optoelectronic and energy applications.
The objective of this study is to investigate the structural and electrical characteristics of the superconducting compound Y1 − xInxBa2Cu3O7 + δ (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized via the standard solid-state reaction method. The critical transition temperature and energy gap were determined using the four-point probe technique, while the structural parameters were quantitatively analyzed using Scherrer, Williamson–Hall (W–H), and size–strain plot (SSP) methods. All substituted samples exhibited metallic behavior in the normal state prior to transitioning to the superconducting state. Notably, the x = 0.3 sample demonstrated an enhanced critical temperature (Tc(offset) = 104.8 K) and a corresponding energy gap of ~0.032 eV. Structural characterization revealed that this concentration yields a minimized crystallite size of 6.118 nm accompanied by a specific induced lattice microstrain of 0.0019. The substitution of Y+3 by isovalent In+3 alters the lattice parameters, which may optimize the physical configuration between the charge reservoir layers and the superconducting CuO2 planes. This study establishes that controlled lattice microstrain induced by appropriate indium substitution plays a critical role in optimizing charge-transfer efficiency and enhancing high-temperature superconductivity within the Y-123 system.
