Highly efficient and stable lead-free cesium copper halide perovskites for optoelectronic applications: A DFT based study

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals show promise as scintillating materials for wide-energy radiation detection, outperforming their three-dimensional counterparts. In this study, we synthesized single crystals of (PEA2-xBZAx)PbBr4 (x ranging from 0.1 to 2), utilizing phenethylammonium (C6H5CH2CH2NH3+) and benzylammonium (C6H5CH2NH3+) cations. These materials exhibit favorable optical and scintillation properties, rendering them suitable for high light yield (LY) and fast-response scintillators. Our investigation, employing various techniques such as X-ray diffraction (XRD), photoluminescence (PL), time-resolved (TR) PL, Raman spectroscopy, radioluminescence (RL), thermoluminescence (TL), and scintillation measurements, unveiled lattice strain induced by dual-organic cations in powder X-ray diffraction. Density functional theory analysis demonstrated a maximal 0.13 eV increase in the band gap with the addition of BZA cation addition. Notably, the largest Stokes shift of 0.06 eV was observed in (BZA)2PbBr4. The dual-organic cation crystals displayed >80% fast component scintillation decay time, which is advantageous for the scintillating process. Furthermore, we observed a dual-organic cations-induced enhancement of electron-hole transfer efficiency by up to 60%, with a contribution of >70% to the fast component of scintillation decay. The crystal with the lowest BZA concentration, (PEA1.9BZA0.1)PbBr4, demonstrated the highest LYs of 14.9 ± 1.5 ph/keV at room temperature. Despite a 55-70% decrease in LY for BZA concentrations >5%, simultaneous reductions in scintillation decay time (12-32%) may work for time-of-flight positron emission tomography and photon-counting computed tomography. Our work underscores the crucial role of dual-organic cations in advancing our understanding of 2D-HOIP crystals for materials science and radiation detection applications.

Effects of La-N Co-Doping of BaTiO3 on Its Electron-Optical Properties for Photocatalysis: A DFT Study

In cation-anion co-doping, rare earth elements excel at regulating the electronic structure of perovskites, leading to their improved photocatalytic performance. In this regard, the impact of co-doping rare earth elements at the Ba and Ti sites in BaTiO3 on its electronic and photocatalytic properties was thoroughly investigated based on 2 × 2 × 2 supercell structures of BaTiO3 with different La concentrations of 12.5% and 25% using DFT calculations. The band structure, density of states, charge density difference, optical properties, and the redox band edge of the co-doped models mentioned above were analyzed. The results indicated that the BaTiO3 structure co-doped with 25% La at the Ti site exhibited higher absorption in the visible range and displayed a remarkable photocatalytic water-splitting performance. The introduced La dopant at the Ti site effectively reduced the energy required for electronic transitions by introducing intermediate energy levels within the bandgap. Our calculations and findings of this study provide theoretical support and reliable predictions for the exploration of BaTiO3 perovskites with superior photocatalytic performances.

Pressure-induced tuning of physical properties in high-throughput metal halide MSn2Br5 (M = K, Cs) perovskites for optoelectronic applications

The physical properties of the ferromagnetic oxide perovskites MSn2Br5 (M = K, Cs) were thoroughly examined using the GGA + PBE formalism of density functional theory. The investigation includes a comprehensive characterization of these materials under hydrostatic pressures ranging up to 25 GPa. Our work represents the first theoretical framework for exploring the behavior of MSn2Br5 (M = K, Cs) under pressure, providing valuable insights into their properties. To ensure the thermodynamic and mechanical stability of the studied compounds, we justified their stability through the analysis of formation energy and Born stability criteria. Furthermore, we conducted a thorough examination of the mechanical features of MSn2Br5 (M = K, Cs) based on various parameters, such as elastic constants, elastic moduli, the Kleinman parameter, the machinability index, and the Vickers hardness. Pugh's ratio and Poisson's ratio data show a ductile behavior for both compounds under stress. Moreover, our analysis of the refractive index suggests that both materials hold significant potential as candidates for ultrahigh-density optical data storage devices, particularly when subjected to appropriate laser irradiation. This finding opens up exciting possibilities for utilizing MSn2Br5 (M = K, Cs) in advanced optical technologies.