Lead-free halide double perovskites, such as Cs2AgBiX6, have emerged as less toxic alternatives to the lead-based solar cell absorbers, APbX3 (where A is a monovalent cation and X is halide). Despite their potential application in photovoltaics and x-ray detectors, halide double perovskites exhibit limited optical properties due to their relatively high band gap and the indirect nature of the band gap. We propose doping by introducing small amounts of Pb2+ into the Cs2AgBiBr6 perovskite structure at the Ag1+ and Bi3+ sites through a controlled solution synthesis. We explored the crystal structure, surface morphology, optical properties, and electronic structure of as-synthesized Pb-doped double perovskite crystals. Using X-ray diffraction and X-ray photoelectron spectroscopy analysis, the formation of Pb-doped Cs2AgBiBr6 double perovskite was confirmed. The crystal structure parameters and band gap values of doped Cs2AgBiBr6 double perovskites, as predicted by density functional theory (DFT) calculations, were validated through XRD and UV/Visible spectroscopy analysis. The strategic Pbdoping assisted in altering the band topology, which resulted in the decrease of disparity between indirect and direct band gaps in Pb-doped perovskite Cs2AgBiBr6. Pb-doping also induced a notable reduction in the energy bandgap of the perovskite compound, making it spectroscopically more relevant, thereby enhancing its applicability in photovoltaics.

The significance of radiation shielding is on the rise due to the expanding areas exposed to ra-diation emissions. Consequently, there is a critical need to develop metal alloys and composites that exhibit excellent capabilities in absorbing neutron and gamma rays for effective radiation shielding. Low-density Ti-based alloys with controlled structural properties can be used for ra-diation protection purposes. The present research investigates boron-doped Ti-based alloy, Ti50Cu30Zr15B5, which is synthesized by arc melting technique, and its structural, mechanical properties, neutron, and gamma-ray transmission rate were investigated. Monte Carlo N-Particle simulation (MCNP6.2) code is used for calculating the Thermal (2.53 x 10-8 MeV) and fast (2 MeV) neutron transmission ratio (I/I0) dependent on the sample thickness. The Phy-x program is employed for calculating the gamma-ray LAC, MAC, HVL, TVL, and MFP values. The calculated neutron shielding performance parameters of Ti50Cu30Zr15B5 alloy were compared with materials in the literature. It was found that Ti50Cu30Zr15B5 alloy demonstrated impressive physical char-acteristics, suggesting that it can serve as a promising alloy for neutron and gamma-ray shielding applications.

Due to their intrinsic stability and reduced toxicity, lead-free halide double perovskite semiconductors have become potential alternatives to lead-based perovskites. In the present study, we used density functional theory simulations to investigate the mechanical stability and band gap evolution of double perovskites Cs2AgBiX6 (X = Cl and Br) under an applied pressure. To investigate the pressure-dependent properties, the hydrostatic pressure induced was in the range of 0-100 GPa. The mechanical behaviors indicated that the materials under study are both ductile and mechanically stable and that the induced pressure enhances the ductility. As a result of the induced pressure, the covalent bonds transformed into metallic bonds with a reduction in bond lengths. Electronic properties, energy bands, and electronic density of states were obtained with the hybrid HSE06 functional, including spin-orbit coupling (HSE06 + SOC) calculations. The electronic structure study revealed that Cs2AgBiX6 samples behave as X-Γ indirect gap semiconductors, and the gap reduces with the applied pressure. The pressure-driven samples ultimately transform from the semiconductor to a metallic phase at the given pressure range. Also, the calculations demonstrated that the applied pressure and spin-orbit coupling of the states pushed VBM and CBM toward the Fermi level which caused the evolution of the band gap. The relationship between the structure and band gap demonstrates the potential for designing lead-free inorganic perovskites for optoelectronic applications, including solar cells as well as X-ray detectors.

Hybrid organic-inorganic halide perovskite, CH3NH3Pb1-xCdxBr3 (x = 0, 0.05, 0.08, 0.10) semiconductor crystals were synthesized using a low temperature assisted crystal growth method. The cubic (Pm-3m) structure was maintained throughout the doping range. At low concentrations the Cd2+ doping exhibited lattice expansion, while at higher dopant concentration the structure reverted back to that of the undoped composition. The non -monotonic doping dependence was reflected in the shift of bond vibrational modes, minimum in bandgap, and longer average photoluminescence lifetime decay tau avg in the 5% doped sample. Photoluminescence (PL) spec-troscopy showed a shift in the luminescence peak from 580 nm to 602 nm for 0% and 10% Cd doped respectively. Time resolved photoluminescence (TRPL) gave an average time decay constant tau avg = 1-3 ns and diffusion length LD-1.1 mu m. The dielectric response exhibited a dynamic frequency and temperature dependence of the meth-ylammonium (MA+) dipole moment.

Here we synthesized halide perovskite absorber CH3NH3PbI3 and CdS as charge transporting layer for perovskite photovoltaic device. Perovskite absorber and CdS were characterized by X-ray diffraction, UV-Visible spectrophotometry and SEM. The energy gap and structure of CH3NH3PbI3 and CdS were found to be suitable for use as absorber and electron transporting layer in perovskite solar cell device respectively. Numerical simulation of CH3NH3PbI3 perovskite solar cells was then carried out using the SCAPS-1D solar cell capacitance simulator software. A perovskite solar cell was simulated for best efficiency by replacing the traditional compact TiO2 layer with CdS (i.e., a hole-blocking layer) because CdS layers possess a greater photostability than TiO2 with continuous illumination of sunlight. We investigated the effect of layer parameters like absorber thickness, bulk defects, and interface defects on the device performance of CdS based perovskite photovoltaic device. It was observed that these parameters have strong impact on open circuit voltage V-oc, short circuit current I-sc,fillfactor (FF) and the power conversion efficiency. The device characteristics and optimization of the solar photovoltaic device was recorded and presented in paper.

By using density functional theory (DFT) in terms of ab-initio investigation, we examined the structural, electronic and magnetic properties of cubic, halide perovskite (RbGeI3) and oxide perovskite (RbDyO3) for the first time. Structural stability of cubic RbGeI3 and RbDyO3 compounds were determined by optimizing the structure in ferromagnetic (FM), non-magnetic (NM), and Anti-ferromagnetic (AFM) phases by using PBE generalized gradient approximation (GGA) functional to find the exchange-correlation potential. From structural optimizations, the nonmagnetic phase of RbGeI3 and the ferromagnetic phase of RbDyO3 was observed to be stable. From the stability curve, we calculated the equilibrium lattices, bulk moduli and their pressure derivatives and equilibrium volume. Moreover, the calculation of tolerance factor for these compounds (τ ≈1) demonstrates the formation of the cubic perovskite structure. The spin magnetic moments of these compounds have been obtained to explore the magnetic properties of RbDyO3. Since, RbGeI3 is nonmagnetic material with zero magnetic moment as also observed from the structural optimization. Rare earths like Dysprosium (Dy) possess strongly localized f-electronic states which are responsible for their strong magnetic properties and other delocalized f-electron states arising from the hybridization of p-d states which determine the electronic properties within the material. The latter situation suits well for RbGeI3 compound. We report a detailed analysis of the different ground state properties for the two compounds using GGA and GGA-modified Becke–Johnson computational approaches.

We report the solution-based synthesis and material characterization of the Cd substituted hybrid organic-inorganic lead halide perovskite CH3NH3Pb1-xCdxI3 (x = 0.0, 0.03, 0.05, 0.08). Structure and morphology of the samples were investigated using XRD, FESEM and HRTEM techniques. XRD results confirmed a tetragonal perovskite structure (I4/mcm) through the doping range. Optical absorption, band gap and bonding character were studied by UV-visible, FTIR and photoluminescence spectroscopy. Oxidation states, binding energy and chemical composition were determined by XPS and EDAX. A low value of Urbach energy (similar to 14 meV) indicated high sample quality with low defects and trap states. The undoped samples had a direct energy gap of 1.56 eV, which reduced to 1.50 eV upon Cd doping. Most significantly, the absorption coefficient of CH3NH3Pb1-xCdxI3 remained high (similar to 10(3)) above 750 nun in the spectrally important infrared range as compared to CH3NH3PbI3, which approached zero. The enhanced structural and optical properties upon Cd doping make these materials promising photo absorber candidates compared to undoped CH3NH3PbI3.

In this work, the numerical simulation of CH3NH3PbI3 perovskite solar cells was undertaken using the scaps-1d solar cell capacitance simulator software. A perovskite solar cell was simulated for best efficiency by replacing the traditional compact TiO2 layer with CdS (i.e., a hole-blocking layer) because CdS layers have been shown to possess a greater photostability than TiO2 with continuous illumination of sunlight. With the view of optimizing the device fabrication of perovskite/CdS thin-film solar cell (TFSC) for maximum efficiency, the perovskite/CdS TFSC structure was optimized theoretically using scaps-1d, which is possible because the perovskite layer has the same configuration and an excitation type as CdTe, copper-indium-gallium-selenide, and other inorganic semiconductor solar cells. Solar cell performance is highly dependent on the layer parameters, and so the effect that absorber thickness, bulk defects, and interface defects have on the device performance was studied and the device was optimized. Further, the effect that atmospheric conditions have on device performance was studied by varying the temperature and illumination density, and the optimum performance was found. After these optimizations, the simulation results show that a perovskite thickness of 500 nm yields an efficiency of 23.83% with a high open-circuit voltage of 1.37 V. These results for this absorber thickness is in good agreement with reports of experimental results for this device.

Organometal halide perovskite (CH3N3PbI3) absorber was synthesized from CH3NH3I and PbI2 in N, N dimethylformamide by solution spin coating process. Characterization by X-ray diffraction, optical and electron microscopy studies confirmed a well-formed nano-crystalline tetragonal pervoskite structure. The synthesized CH3NH3PbI3 was used as a photo absorber material in a hole-conductor free photovoltaic device with TiO2 as an electron conductor. This configuration of the perovskite photovoltaic device exploits the role of CH3NH3PbI3 simultaneously as light absorber and hole-conducting material. We report two device configurations: (a) with a compact TiO2 buffer layer introduced between the porous TiO(2 )and FTO and (b) without the compact TiO2 layer over the FTO substrate. The simple solar cell structure FTO/TiO2/CH3NH3PbI3/Agpresented here shows good photovoltaic performance under illumination with standard AM1.5 sunlight. For the champion devices from the two structures, (a) and (b), we obtained short circuit photocurrent densities asJ(sc) = 17.4 mA/cm(2) and 19.5 mA/cm(2) , open circuit voltage V-oc = 1.0 V and 1.45 V, fill factor FF = 0.54 and 0.29 and a power conversion efficiency (PCE) of 9.39% and 8.19% respectively under solar light intensity flux of 100 mW/cm(2). We find that structure (a) offers significantly better device parameters. The results of the present work suggest a route to realize a simple, low cost and highly efficient perovskite photovoltaic device. These devices could be realized in miniaturized sensors and electronic components applied in Internet of Things (IoT). (C) The Author(s) 2018. Published by ECS.

Doping of semiconductors in a controlled mannner have paramount technological importance as far as the optical and electronic properties of the devices are concerned. Hybrid organic-inorganic perovskites (HOPs) as intrinsic semiconductors have sensational properties required for both the solar photovoltaics and perovskite light emitting diodes. However, undoped and complexity in the dpoing process of HOPs have limited their exploitation in the field of elcronics. In this papper we present the synthesis of HOP semiconductor (CH3NH3PbI3) doped in Pb2+ position by Cd2+. We studied the effect of the incorporation of Cd2+ into the crystalline structure and analysed the changes in the properties like crystal structure, optical absorption and the surface morphology. The structure of HOPs confirmed by X-ray diffraction analysis is tetragonal perovskite type. It can be found that the crystallinity of the samples was enhanced with the doping concentration as the intensity of diffraction peaks were observed to increase with doping. The absorption spectra as obtained from UV-Visible spectrophotometry and Tauc plot analysis indicated that the band gap observed (1.73 eV) is direct type and gets reduced to 1.67 eV with the doping concentration. The red shift may be due to the increase in the size of nanocrystalline material with doping.

First principle calculations with highly precise spin-polarized density functional theory (DFT) have been performed to study the structural stability, mechanical and magneto-electronic properties of cubic perovskite BaBkO3. The properties were studied under the generalized gradient approximation (GGA) and onset Coulomb interaction by WEIN2k package. The DFT and analytically calculated values of Goldschmidt tolerance (GT) factor in addition to stable-phase optimization show stability of the present material in the ferromagnetic cubic phase with a higher magnetic moment of 7 mu B. This is because the nature of magnetism of 5f actinide materials (l = 3) is governed by the large spin-orbit interaction and the hybridization of 5f electron orbitals with other states. The value of exchange and correlation potential were treated with different approximations: GGA and GGA + U calculations. Contribution of electronic states was studied through total and partial density of states using GGA and GGA + U approach. GGA + U calculations reveal an indirect band gap of 3.15 eV for BaBkO3 in the spin down channel supporting the half metallic nature and spin-polarized electronic band structure encourages complete spin polarization of the material with metallic character in spin up state. Mechanical properties like stability, stiffness, hardness, brittleness and ductility were discussed on the basis of elastic parameters obtained. The oxide perovskite BaBkO3 exhibit higher value of Seebeck coefficient and power factor at room temperature with a value of 150 mu VK-1 and 5.1 x 10(12) mu Wcm(-1) K(-2)s(-1) respectively. The properties of half-metallicity and higher Seebeck coefficient makes this material a promising candidate for thermoelectric and spintronic device applications. (C) 2018 Published by Elsevier B.V.

Authors Khursheed Ahmad Parrey and Shakeel Ahmad Khandy included the names of Asad Niazi, Anver Aziz, and S. G. Ansari as co-authors of this article without their permission.

Double perovskite La 2 NbMnO 6 was systematically studied using the first-principles calculations. The structural, electronic, optical and transport properties of this compound were calculated. Spin resolved band structure predicted this material as a half-metal with an energy gap of 3.75 eV in spin down state. The optical coefficients including optical conductivity, reflectivity and electron energy loss are calculated for photon energy up to 30.00 eV to understand the optical response of this perovskite. The strong absorption of all the ultraviolet and infrared frequencies of the spectrum by this material may suggest the potential application of this material for the optoelectronic devices in ultraviolet and infra-red region. Also, the thermoelectric properties with a speculation from the half-metallic electronic structure are reported. Subsequently, the Seebeck coefficient, electrical and thermal conductivity coefficients are calculated to predict the thermoelectric figure of merit (zT), the maximum of which is found out to be 0.14 at 800 K.

First principles calculations on the thermodynamic properties of PbTaO3 and SnAlO3 in a temperature range from 0 K to 800 K and pressure range from 0 GPa to 30 GPa have been carried out within the framework of density functional theory (DFT). The band structures of these oxides at different pressures display an increase in metallic character with a concomitant decrease in lattice constants, while the bulk modulus increases with increasing pressure. The thermal concert of these materials has been analyzed in terms of the temperature and pressure variation in Debye temperature, thermal expansion, entropy, and the Grüneisen parameter. Debye temperatures have been calculated from the elastic parameters as well as the quasi-harmonic Debye model, which are 339.07 GPa for PbTaO3 and 714.36 GPa for SnAlO3.

Overall thermal dependence of electronic, thermodynamic and mechanical properties of BaNpO3 oxide have been investigated via full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). Different approximations such as local density approximation (LDA), generalized gradient approximation (GGA), Hubbard approximation potential (GGA+U) have been employed to achieve the optimized calculation results. The calculated structural, electronic and mechanical parameters are consistent with the available experimental and theoretical data. The elastic parameters at different pressures have also been calculated. Half-metallic nature is reflected from the spin polarized band profile of the present material. Moreover, the temperature and pressure dependent thermodynamic properties including Debye Temperature, specific heat capacity, grueinessien parameter, Entropy, thermal expansion, etc have been calculated via quasiharmonic Debye model.