Nurul Islam

Pristine BaTiO₃ (BTO) and Agdoped BaTiO₃ thin films (2–6 at. %) were synthesized on glass substrates at 300 °C using a costeffective spray pyrolysis technique. Ag incorporation initially reduced grain size up to 4 at. % and increased it at 6 at.%. XRD confirmed the tetragonal phase, with higher doping inducing lattice distortion and increased micro-strain. Optical analyses revealed an indirecttodirect bandgap transition accompanied by a reduction from 2.83 eV to 2.28 eV and a redshift in absorption due to Ag4d/O2p hybridization and oxygenvacancy states. Temperaturedependent resistivity indicated trapassisted smallpolaron hopping at low doping and partial mobility recovery at higher levels. DFT results supported Aginduced states near the valenceband maximum and a transition to a direct bandgap, highlighting potential for photovoltaic applications.

Eco-friendly inorganic lead free metal halide double perovskites have versatile applications in optoelectronic and photovoltaic devices. In this manuscript, we have studied structural, thermodynamic, electronic, optical and mechanical properties of pressure induced Cs₂gBiCl₆ samples. The phase stability is confirmed by the tolerance and octahedral factor calculations. The thermodynamic parameters such as enthalpy, free energy, entropy, and heat capacity are observed based on the phonon modes. The indirect band gap is tuned to direct band gap by disordering of Ag⁺/Bi³⁺ cations in their sub-lattice. In this study, the induced pressure is varying from 0 to 80 GPa. We have seen at 80 GPa hydrostatic pressure, Cs₂AgBiCl₆ sample has tuned a bang gap energy semiconductor to metallic one. Under induced pressure, the bond lengths are reduced due to crystal defect, occurring within Ag and Bi atoms. The narrow band gap and the partial density of states of disordered Cs₂AgBiCl₆ refers that the migration of charge carriers to the surface to facilitate the photocatalytic reaction. The absorption edge shifted towards the lower energy region with varying pressure. Meanwhile, pressure-driven material increase symmetry breaking in [AgBi]^-6 and [AgCl]^-6 octahedral, which decreases total energy due to reduced band gap energy. Phase transition double halide material produces outstanding properties, giving a new avenue of device applications. The mechanical nature demonstrates that pristine and pressure driven Cs₂AgBiCl₆ samples may be suitable for optoelectronic and photovoltaic device applications.

Non-toxic lead-free halide metal perovskites have gained significant interest in photovoltaic and optoelectronic device applications. In this manuscript, we have studied the structural, electronic, mechanical, and optical properties of eco-friendly cubic CsSn_1−xCu_xI₃, (x = 0, 0.125, 0.25, 0.5, 1) perovskites applying first-principles pseudopotential-based density functional theory (DFT). Cu-doped CsSnI₃ has a large impact on the band gap energy viz. the transition of direct band gap towards the indirect band gap. The mechanical properties demonstrate that the pristine and Cu-doped CsSnI₃ samples are mechanically stable and their ductility is enhanced by Cu doping. The mechanical stability and ductility favors the suitability of pure and Cu-doped samples in the thin film industry. The absorption edge of Cu-doped CsSnI₃ moves towards the lower energy region in comparison with their pure form. In addition, the high dielectric constant, high optical absorption, and high optical conductivity of Cu-doped CsSnI₃ materials suggests that the studied materials have a broad range of applications in optoelectronic devices, especially solar cells. A combined analysis of the structural, electronic, mechanical and optical properties suggests that CsSn_1−xCu_xI₃, (x = 0, 0.125, 0.25, 0.5, 1) samples are a suitable candidate for photovoltaic as well as optoelectronic device applications.

Inorganic double halide perovskites have a wide range of applications in low-cost photovoltaic and optoelectronic devices. In this manuscript, we have studied their structural, electronic, mechanical and optical properties using density functional theory (DFT) simulations. In this work, hydrostatic pressure is induced from 0 to 50 GPa. Disordered Ag and Bi atoms have a large impact on band gap energy; in this case, the indirect band gap is transferred towards a direct band gap. We have seen that pressure-driven samples have transformed a band energy semiconductor into a metallic one. Under the induced hydrostatic pressure, the covalent bond is transformed into a metallic bond and the bond lengths are reduced. Meanwhile, pressure-induced samples enhance symmetry breaking in [AgBr₆]⁵⁻ and [BiBr₆]³⁻ octahedra, which reduces the density of states of the Fermi surface and lowers the total energy. The mechanical behaviors demonstrated that the studied materials are mechanically stable as well as ductile and their ductile nature is enhanced by the driving pressure. The absorption peak is shifted towards the low energy region with increased hydrostatic pressure. The absorptivity and dielectric constant values are also increased with driving pressure. Phase transformed double halide perovskites triggered by outside stimuli produce several outstanding materials properties, giving great scope for a broad range of applications. This type of pristine and disordered double halide perovskite with pressure-driven semiconductor-to-metal phase transition samples may have potential applications in optoelectronic and photovoltaic devices.