Electronic Band Gap Research Articles

Structural, magnetic, optical, and electronic properties of vanadium-doped barium hexaferrite nanoparticles: Experimental and DFT approaches

Vanadium-doped barium hexaferrite with a nanostructure is a highly valuable material in various technological fields, such as electronics, permanent magnets, and sensors. The Ba1-xFe12-xVxO19 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) nanoparticles derived from the aqueous solutions containing Fe:Ba molar ratio of 10:1 through the sol-gel auto-combustion method. Computational study was also performed using the first-principles density functional theory (DFT) approach. Crystal structure optimization, band structure, and density of states (DOS) calculations were conducted by CASTEP code. The variation of the structural, magnetic, optical, morphological, and electronic properties of V5+-doped barium hexaferrite was investigated. The XRD analysis combined with the Rietveld refinement showed the hexagonal structure of M-type barium ferrite (BaM), confirmed by the FT-IR analysis. The morphology of BaM nanoparticles was studied by the FE-SEM and TEM micrographs. In addition, magnetic and optical properties were analyzed through VSM and UV–Vis analysis. Crystallite size was found to be highly effective in tuning the coercivity and optical band gap of barium hexaferrites, which varied, respectively, from 3.24 to 4.83 kOe, and 2.69–3.69 eV. Magnetic results showed that several variables like cations distribution, lattice strain, and hematite secondary phase affected the nanoparticles’ magnetization. The DFT simulation results showed a sharp reduction of electronic band gap energy whether V takes the position of Ba or Fe (from 1.10 eV in undoped to 0.64 and 0.14 eV in doped structures). The projected density of states (PDOS) calculations demonstrated that the d orbitals of V and Ba mainly contribute to the valence band maximum (VBM) and conduction band minimum (CBM), respectively.

First-Principles insights to probe structural and opto-electronic properties of [formula omitted] (Y=Mg, Sr) halide perovskites with variety of DFT methods

This study reports the structural, electronic, optical, phonon, thermodynamic and thermoelectric properties of AgYF3 (X=Mg, Sr) for photovoltaic and energy applications. We performed first principles calculations using full potential linearized augmented plane wave, FP-LAPW method implemented in Wien2k. The generalized gradient approximations of Perdew–Burke–Ernzerhof PBE-GGA, and PBE revised for solids, PBEsol, is employed for structural optimization of these lead free halide perovskites. The Birch–Murnaghan energy volume curve fitting comprehend the structural stability. The optimized lattice constant of AgMgF3 and AgSrF3 obtained with PBE-GGA(PBEsol) is 3.99(3.92)Å and 4.42(4.65)Å. The stability is further tested with the help of formation energy and positive phonon dispersion curves calculations. For the calculations of explicit electronic and optical properties, we also employed Tran–Blaha modified Beck–Johnson (TB-mBJ) and Strongly Constrained but Appropriately Normed, SCAN, exchange and correlations functionals. The electronic band gap of AgMgF3 computed with PBEsol, TB-mBJ and SCAN is 1.96 eV, 5.25 eV and 2.59 eV exhibiting M-Γ indirect band gap. The band gap energy of AgSrF3 is 2.06 eV, 6.42 eV and 2.70 eV with PBEsol, TB-mBJ and SCAN. The indirect band gap nature of AgSrF3 is confirmed by PBEsol and TB-mBJ while it anticipated direct band gap behavior with meta-GGA SCAN. The different optical parameters like dielectric constant, optical conductivity, energy loss function, absorption, reflectivity and refractive index are calculated to assess optical activity of both perovskites. Comprehensive electronic and optical analysis advocates the utility of AgMgF3 and AgSrF3 for different applications is solar technology and optoelectronic devices.

Effect of Cr doping on electronic and optical properties of mono/bilayer MoTe2 nanosheets– a first-principles study

The influence of Cr-doping on mono/bilayer MoTe2 nanostructures is studied within the framework of density functional theory (DFT) since doping may be used to effectively tailor the electronic and optical characteristics in a desired manner. Chromium (Cr) seems to modify the electronic properties and energy band gap of MoTe2 considerably. At first, we confirmed the stability of the proposed structure with the support of cohesive formation energy and phonon-band-spectrum. Moreover, doping with Cr on MoTe2 produces a red shift towards far infra-red region in the absorption coefficient, thus making it suitable for far infra-red region applications. Hence, Cr doping is employed in this work. When Cr impurities are substituted in pristine MoTe2 nanostructures, the band structure gets modified. Additionally, the band gap of mono/bilayer MoTe2 nanostructures reduces from 1.143/0.74 eV for pristine MoTe2 to 0.807/0.621 eV for 8 % substitution of Cr. By examining absorption spectra, it was found that the optical characteristics of mono/bilayer MoTe2 changed significantly with doping of Cr impurities. The results of this study provide insight into the band structure, optical, and electronic attributes of mono/bilayer MoTe2 nanostructures that could be further fine-tuned for optoelectronic applications using substitution of Cr impurities.

Harvesting Magneto-Acoustic Waves Using Magnetic 2D Chromium Telluride (CrTe3).

A vast majority of electrical devices have integrated magnetic units, which generate constant magnetic fields with noticeable vibrations. The majority of existing nanogenerators acquire energy through friction/mechanical forces and most of these instances overlook acoustic vibrations and magnetic fields. Magnetic two-dimensional (2D) tellurides present a wide range of possibilities for devising a potential flexible energy harvester. 2D chromium telluride (2D CrTe3) is synthesized, which exhibits ferromagnetic behavior with a higher T c of ≈224 K. The structure exhibits stable high remnant magnetization, making 2D CrTe3 a potential material for harvesting magneto-acoustic waves. A magneto-acoustic nanogenerator (MANG) is fabricated and the basic mechanical stability and sensitivity of the device with change in load conditions are tested. A high surface charge density of 2.919 mC m-2 is obtained for the device. The thermal strain created in the lattice structure is examined using in-situ Raman spectroscopy. The magnetic anisotropy energy (MAE) responsible for long-range FM ordering is calculated by theoretical modelling with insights into opening of electronic bandgap which enhances the flexoelectric effects. The MANG can be a potential NG to synergistically tap into the magneto-acoustic vibrations generated from the frequency changes of a vibrating device such as loudspeakers.

Uniaxial Strain Engineering of Anisotropic Phonon in Few‐Layer Violet Phosphorus with High Stretchability for Polarized Sensitive Flexible Photodetector

AbstractThe manifestation of mechanical phenomena in quantum materials at the macroscopic level is intricately linked to pronounced electron‐electron interactions within their lattices, a relationship that becomes especially evident in low‐dimensional materials. Violet phosphorous (VP), a nascent 2D material distinguished by its unique vertically aligned tubular structures, has garnered considerable attention owing to its layer‐dependent electronic bandgap, exceptional carrier mobility, and robust air stability. Herein, a comprehensive exploration of the phonon modes exhibited by few‐layer VP through an integrated experimental‐theoretical approach, focusing on the modulation of their Raman response under the uniaxial strain along a‐axis, b‐axis, and tube direction, respectively, is undertaken. Density functional theory calculations highlight when strain is applied along the a‐ or b‐axis direction, the strain is predominantly mitigated through tube rotational adaptations instead of the change of bond length and bond angle, culminating in a pronounced anisotropic Raman response. Moreover, the strain engineering can effectively optimize the photoelectric response performance of VP, including increase the responsivity ≈2500% and elevate the anisotropic ratio from 2.26 to 3.38. This investigation not only confirms the superior stretchability and impact resistance properties of cross‐structured VP but also establishes the groundwork for exploring the strain‐induced anisotropic optoelectric properties to VP.

A theoretical analysis of the effect of hydrostatic pressure on cerium oxide for renewable energy applications

The characteristics of cubic cerium oxide (CeO2) have been investigated using density functional theory (DFT) using the PBE-GGA exchange–correlation functional. This study mainly focused on the structural, elastic, and optoelectronic properties of the CeO2 under the application of external hydrostatic pressure. It is observed that lattice constants and volume tend to decrease with increasing pressure. Based on the observed trends in lattice constants variations, CeO2 exhibits compressibility at high-pressure conditions, although it remains structurally unchanged throughout the pressure range of 0 to 100 GPa. Applying pressure within the range of 0 to 100 GPa reveals a distinct characteristic associated with the emergence of electronic bandgap opening. The material displays an indirect energy bandgap, with its magnitude increasing from 2.659 eV to 4.055 eV under rising pressure. To deeply understand the impact of external pressure on the optical behaviour of CeO2, extensive investigation has been conducted on several optical parameters such as the dielectric function, refractive index, optical reflectivity, absorption coefficient, optical conductivity, and loss function throughout the energy range up to 50 eV. However, there is a tendency for optical parameters to show sharpening peaks that shift somewhat towards higher energies. Furthermore, we have also tested the impact of bandgap modulation induced in CeO2 by proposing a CsSnBr3-based solar cell with the One-Dimensional Solar Cell Capacitance Simulator software. Based on our findings, the use of cubic cerium oxide may find its potential to enhance the performance of optoelectronic and renewable energy devices.

Stable novel silicon allotropes in space group P2/m with various band gap structures by high-throughput screening

Silicon is the fundamental material for the semiconductor and microelectronics industries, but controlling the electronic band gap structure of diamond-type silicon remains a huge challenge to adapt to growing applications. Here, we have predicated 23 new silicon allotropes in space group P2/m from 279 possible structures by high-throughput screening accompanied by graph and group theory based on random strategy (RG2) code. The mechanical, electronic and optical properties of these structures were studied in detail. These novel silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. These new silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. Besides different electronic bandgap structures, all 23 structures exhibit strong absorption in the visible light region and P2/m-15 demonstrates the excellent mechanical properties (Bulk modulus beyond 80 GPa). Based on their nice stability, good mechanical, electronic and optical properties validated by the ab inito molecular dynamics simulation, phonon spectra and density functional theoretical calculations, these predicted silicon allotropes provide not only ideas for the synthesis of new silicon allotropes but also dawn for expanding the application of semiconductor materials.

Study of structural, mechanical, thermal, and electronic structure properties of A2SnCl6 (A = Cs, Rb) perovskites for energy generation applications

The structural, mechanical, thermal, and electronic structure properties of lead-free vacancy-ordered perovskites A2SnCl6 (A = Cs, Rb) were investigated by first-principles calculations under pressure in the DFT framework. DFT is used to study the effect of pressure (0–40 GPa) on these properties of A2SnCl6 (A = Cs, Rb) perovskites. The mechanical parameters show that these two perovskites in nature are mechanically stable, anisotropic, and ductile. It is shown that, as pressure increases, the electronic band gap of Cs2SnCl6 and Rb2SnCl6 increases from 3.495 eV to 4.958 eV and 3.446 eV to 4.722 eV, respectively. Electronic structure calculations show that Sn s orbitals and halogen Cl p orbitals mainly form the conduction band through combination, while the valence band consists only of halogen Cl p orbitals. The mechanical and electronic properties analysis proposes that these two perovskites are potential candidates for optoelectronic applications that work under changing pressure and altitude.

Dft-based nano architectonics: Exploring Structural, Mechanical, and optoelectronic properties of halide double perovskites K2ScAgX6 (X=Cl, Br and I)

This report details a computational analysis of the various characteristics of newly developed double perovskites (DPs) K2ScAgX6 (where X =Br, Cl, and I), with an emphasis on their potential uses in energy storage and solar energy sector. Through the application of Density Functional Theory (DFT); the structural, mechanical and optoelectronic properties of these DPs materials have been investigated. The cubic phase of K2ScAgX6 DPs was confirmed, with tolerance factor (τ) values of 0.818, 0.812, and 0.804 for X =Cl, Br and I, respectively. Elastic parameters were used to determine the ductility, anisotropic features and mechanical stability of these materials. The presence of an indirect bandgap (Eg) has been determined via density of states and electronic bandgap computations, yielding values of 2.14 eV for K2ScAgCl6, 2.05 eV for K2ScAgBr6, and 1.98 eV for K2ScAgI6 using the modified Becke–Johnson (mBJ) potential within the Generalized Gradient Approximation (GGA). This research also investigated the absorption of light energy, polarization, optical loss, refractive index across the energy spectral range from 0 to 8 eV. These results indicate that these compounds have significant absorbance and conductivity in the visible and ultraviolet (UV) energy ranges, while remaining transparent to lower-energy photons. This computational study suggest that these complex perovskite materials are highly suitable for energy related applications, and offering significant potential for future experimental investigation.

Nitrogen-rich carbon nitride with heptazine phase controlled by pyrolysis temperature towards photocatalytic U(VI) reduction

Photocatalytic process is a new and efficient technology, which has great potential in the U(VI) reduction process. Nitrogen is volatile at high temperatures, so its synthesis reaction is significantly influenced by pyrolysis temperature. Herein, a series of nitrogen-rich carbon nitride with different nitrogen content and different catalytic properties were prepared by changing the pyrolysis temperature from 450 °C to 650 °C. With the increase of pyrolysis temperature, the nitrogen content decreases continuously, and the triazine ring, tetrazine ring and azo bond generated by low temperature pyrolysis are gradually replaced by heptazine ring and nitrogen single bond. The nitrogen-rich carbon nitride synthesized at 550 °C has the best reducing activity for U(VI) reduction, which is attributed to the good cavity structure, narrow light absorption band gap and high electron transport channel. These results can provide guidance for regulating the electron transport structure of the nitrogen-rich carbon nitride to achieve enhanced photocatalytic activity.

First-Principles Studies of the Electronic and Optical Properties of Two-Dimensional Arsenic-Phosphorus (2D As-P) Compounds.

In this work, we propose the construction of a two-dimensional system based on the stable phases previously reported for the 2D arsenic and phosphorus compounds, with hexagonal and orthorhombic symmetries. Therefore, we have modeled one hexagonal and three possible orthorhombic structures. To ensure the dynamical stability, we performed phonon spectra calculations for each system. We found that all phases are dynamically stable. To ensure the thermodynamic and mechanical stabilities, we have calculated cohesive energies and elastic constants. Our results show that the criteria for the stabilities are all fulfilled. For these stable structures, we computed the electronic and optical properties from first-principles studies based on density functional theory. The computation of electronic band gaps was performed by using the GW approximation to overcome the underestimation of the results obtained from standard DFT approaches. To study the optical properties, we have computed the dielectric function imaginary part within the BSE approach, which takes into account the excitonic effects and allows us to calculate the exciton binding energies of each system. The study was complemented by the computation of the absorption coefficient. From our calculations, it can be established that the 2D As-P systems are good candidates for several technological applications.

Stability and Optoelectronic Properties of Two-Dimensional Gallium Phosphide.

Using first-principles calculations, density functional theory, and the tight-binding method, we investigate the optoelectronic properties of two-dimensional gallium phosphide (2D GaP). Our investigation covers electronic properties, such as band structure and electronic band gap, and optical properties, including absorption spectra, refractive index, and reflectivity, considering excitonic effects. Additionally, structural aspects such as stability, elastic properties, and Raman and infrared spectra are also analyzed. This comprehensive study brings up valuable insights into 2D GaP physics, evincing the key features that make it a potential material for optoelectronic applications, such as photodetectors and solar cells.

On-Surface Synthesis of Graphene Nanoribbons and Spin Chains

Recent advances in on-surface synthesis has allowed the selective fabrication of a number of prototypical types of graphene nanoribbons. The thereby achieved properties include width-dependent electronic band gaps in armchair graphene nanoribbons, edge-localized states in zigzag graphene nanoribbons and topological band engineering in width-modulated topological graphene nanoribbons. More recently, on-surface synthesis of magnetic nanographenes has been reported. Here, the spin originates from unpaired electrons present in nanographenes with controlled sublattice imbalance or topological frustration. The corresponding magnetic moments live in p-orbitals and are hence largely delocalized, which allows for chemical control over their exchange interaction when covalently linking several molecular building blocks. Here, I will present synthesis of various prototypical magnetic nanographenes and the possibility to covalently link them to form coupled spin systems where exchange coupling can exceed 100 meV. Using halogen-substituted precursors, we achieve the on-surface synthesis-based deterministic bottom-up fabrication of various spin chains including a triangulene spin-1 chain revealing the predicted Haldane gap and fractional excitations at the chain termini or a strictly alternating spin-½ chain with chemically engineered coupling strengths J1 and J2 . Scanning tunneling microscopy and spectroscopy is used to explore length- and site-dependent magnetic excitations. Furthermore, we apply hydrogenation to achieve spin site passivation and controlled tip-based local reactivation to fabricate and characterize specific spin patterns in one-dimensional spin chains and spin clusters.

Solid Solution Behavior of High Performance BiOBrxI1-X Photoanodes Probed Using Solid-State NMR, XRD and Optical Spectroscopy

Bismuth oxyhalides (BIOX) are a family of solution-synthesizable 2D layered semiconductors constituted of earth-abundant elements namely bismuth, oxygen and the halogens. BIOX based thin films and heterojunctions are the subject of immense scientific interest due to their impressive performance in photocatalytic and photoelectrochemical devices. Solid solutions of Br/I bismuth oxyhalides exhibit continuously tunable absorption and emission spectra similar to that observed in mixed halide MAPbClxBryI3-x-y perovskites and mixed anion III-V GaAsxP1-x semiconductors. The excited state decay showed two components for all the mixed halide BiOX semiconductors with a dominant short-lived component in the nanosecond range and a weaker longer-lived component of ~100 ns. The average photoluminescence (PL) lifetime varied from 5.4 ns in bare BiOI to 1.49 ns in bare BiOBr with intermediate compositions exhibiting monotonically increasing average PL lifetimes with increasing iodine content. Using a combination of characterization techniques such as solid-state nuclear magnetic resonance (ssNMR), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and optical spectroscopy, we demonstrate the formation of atomic level solid solutions in Br/I bismuth oxyhalides. Through refinement of the lattice parameters using powder XRD and complementary atomic-level 209Bi SSNMR spectroscopy, we found that Vegard's law was obeyed by the BIOBrxI1-x solid solutions. By varying the Br:I ratio, it is also possible to tune the electronic band gap as well as the energy levels corresponding to the conduction band minimum (ECB, min) and the valence band maximum (EVB, max), thus allowing control over the thermodynamic driving force available to drive chemical reactions using photogenerated or electrically injected charge carriers. Suppression of the longitudinal optical phonon in solid solutions of Br/I bismuth oxyhalides is suggestive of lower phonon scattering of charge carriers and improved electronic transport. A synergistic enhancement of more than 1 order of magnitude in the photoelectrochemical water-splitting performance was obtained for the optimized solid solution (BiOBr0.67I0.33) under AM 1.5G 1 sun illumination. Our results pave the way for a one pot synthesis protocol to form BiOX thin films, powders and colloidal suspensions with deterministic control over the stoichiometry.

(Keynote) High-Performance Carbon Nanotube Transistors for Logic Platform

Low-dimensional 1D and 2D materials hold promise as candidate channel materials for highly scaled and high-performance transistors beyond the limits of silicon-based transistors. This talk will first motivate transistors built on low-dimensional channels due to the significant speed, energy efficiency, and transistor density benefits enabled by their electronic and physical properties. This talk will focus on 1D carbon nanotube (CNT) semiconductors and describe the advanced device component process modules that have been demonstrated, explaining both the fundamental mechanisms of operation and device-level performance objectives. Single-CNT FET experimental studies give insight into the quality of (1) low resistance N- and P- contacts down to 10 nm contact length, (2) high-capacitance gate dielectrics optimized for deposition on SP2 carbon surfaces, and (3) controlled N- and P- remote dielectric doping. To achieve high current density each transistor must contain multiple CNTs, therefore we will review state-of-the-art strategies to assemble densely aligned arrays of CNT with controlled CNT spacing between 2-10 nm and uniform electronic bandgap. The final portion of the talk will highlight recent advances from our team and others to integrate the best device components together to demonstrate high-performance carbon nanotube MOSFETs. We will elaborate on the remaining challenges and provide a summary of device design tradeoffs that will help guide future studies.We are grateful for support and collaboration from TSMC Corporate Research, DoD, Stanford SystemX Alliance, Stanford Nanofabrication Facility, Stanford Nano Shared Facility, and the University of California at San Diego.

Pressure induced structural and electronic band transition in CsPbBr3

Cesium lead bromide (CsPbBr3) is a prominent halide perovskite with extensive optoelectronic applications. In this study, we report the pressure modulation of CsPbBr3’s crystal structure and electronic properties at room temperature up to 5 GPa. We have observed a crystal structure transition from the orthorhombic Pnma space group to a new monoclinic phase in the space group P21/c at 2.08 GPa. The structure is associated with ~8% of density jump across the transition boundary. DFT calculations have suggested that the structure transition leads to a change in the electronic band structure, and there is an emergent indirect bandgap at the Pnma-P21/c phase transition boundary at 2.08 GPa. Across the transition boundary, the electronic band gap of CsPbBr3 increased from 2.07 eV to 2.38 eV, which explains its pressure-induced color change. Our study demonstrates the importance of using in-situ crystal structure in the electronic band structure calculations in halide perovskites.

Ab-initio investigation of stability and electronic properties of new yttrium-based solid solution of double transition metal YMXTx (M= Ti and zr; X= C and N; Tx= H, O, and F) MXenes

In this study, an extensive examination was carried out to explore the stability, and physical characteristics of a novel solid solution comprising two transition metals, namely YMXTx (M = Ti and Zr; X = C and N; Tx = H, O, and F) MXenes. The Quantum-Espresso computational package which is based on density functional theory (DFT) and pseudopotential techniques has been employed for performing calculations. The results obtained from the investigation of the structural, dynamic, and mechanical stability revealed that the YTiX and YZrX MXenes exhibited remarkable stability. These findings strongly suggest the feasibility and potential success of experimental synthesis of these materials. Furthermore, the result of cohesive energy indicated that Nitride-based MXenes (Y(Ti/Zr)N) are more stable than Carbide-based MXenes (Y(Ti/Zr)C). By performing comprehensive calculations of the total density of states and band structures, using various approximations such as LDA, GGA, and GGA + HSE06, the investigation revealed a metallic behavior in YMX MXenes. Additionally, the analysis of the TDOS revealed the presence of a pseudogap close to the Fermi level. This observation provides further evidence for the structural stability of the investigated mentioned MXenes. After undergoing saturation with different functional groups, it was observed that the YTiNH2 and YTiNF2 MXenes displayed semiconducting behavior, whereas YZrNO2 is classified as a non-conductive material, and the remaining monolayers exhibit metallic properties. Analyses of charge density and electron localization functions confirmed the metallic behavior of the studied MXenes. Modifying the electronic band gap of 2D MXenes, while also preserving structural stability, could lead to enhancing the application of these materials in optoelectronic devices.

Tuning of Band Gap of Cathode Li2NiPO4F by Replacing P to Nb and Forming Li2NiNbO4F for Application as 5 V Cathode in Lithium Ion Battery: A Density Functional Theory Study

Electrochemical properties of Li2NiPO4F were studied using density functional theory. The obtained voltage, electronic band gap, capacity (∼ for 2 Li+ extraction) and energy density are achieved as 5.33 V, 4.0 eV, 287.3 mAh g−1 and 1531.31 Wh kg−1, respectively. Although, the electrochemical properties of Li2NiPO4F are promising, large electronic band gap would certainly pose a limitation for its commercial application. Nb is a transition metal and its electronegativity is 1.6 which is less than the electronegativity of 2.19 for P. This implies, less operating voltage would be obtained if we replace P in Li2NiPO4F by Nb to form Li2NiNbO4F. However, electronic configuration of Nb is [Kr] 4d45 s1 and the valance state of Nb in Li2NiNbO4F is +5, which in turn specify that, localized Nb d states will reside in conduction band of Li2NiNbO4F and hence the electronic band-gap would be less owing to this localized Nb-d states. Our speculation gets verified by the calculated properties of Li2NiNbO4F obtained through DFT as follows; Voltage, electronic band gap, capacity (∼ for 2 Li+ extraction) and energy density achieved, respectively, are 5.01 V, 3.64 eV (less than LiFePO4), 215.71 mAh g−1, 1080.71 Wh kg−1. Lower electronic band gap of Li2NiNbO4F makes it an alternative to Li2NiPO4F.

Investigating the effects of hydrostatic pressure on the physical properties of cubic Sr3BCl3 (B = As, Sb) for improved optoelectronic applications: A DFT study

This article explores changes in the structural, electronic, elastic, and optical properties of the novel cubic Sr3BCl3 (B = As, Sb) with increasing pressure. This research aims to decrease the electronic band gap of Sr3BCl3 (B = As, Sb) by applying pressure, with the objective of enhancing the optical properties and evaluating the potential of these compounds for use in optoelectronic applications. It has been revealed that both the lattice parameter and cell volume exhibit a declining pattern as pressure increases. At ambient pressure, analysis of the band structure revealed that both Sr3AsCl3 and Sr3SbCl3 are direct band gap semiconductors. With increasing pressure up to 25 GPa the electronic band gap of Sr3AsCl3 (Sr3SbCl3) reduces from 1.70 (1.72) eV to 0.35 (0.10) eV. However, applying hydrostatic pressure enables the attainment of optimal bandgaps for Sr3AsCl3 and Sr3SbCl3, offering theoretical backing for the adjustment of Sr3BCl3 (B = As, Sb) perovskite's bandgaps. The electron and hole effective masses in this perovskite exhibit a gradual decrease as pressure rises from 0 to 25 GPa, promoting the conductivity of both electrons and holes. The elastic properties are calculated using the Thermo-PW tool, revealing that they are anisotropic, ductile, mechanically stable, and resistant to plastic deformation. Importantly, these mechanical properties of both compounds are significantly enhanced under pressure. Optical properties, including the absorption and extinction coefficients, dielectric function, refractive index, reflectivity, and loss function, were calculated within the 0–20 eV range under different pressure conditions. The calculated optical properties highlight the versatility and suitability of Sr3AsCl3 and Sr3SbCl3 perovskites for pressure-tunable optoelectronic devices.

Investigation of structural, electronic, and optical properties of halide perovskites with different amide cations: A first-principles approach

Hybrid halide perovskites (CH3NH3PbI3) have emerged as an appealing candidate in photovoltaic devices due to their low-cost fabrication and remarkable optical and electronic properties. However, the commercial applications of these perovskites are limited by their instability due to the rapid rotation and orientation of methylammonium cation (CH3NH3+), and interaction with PbI2 lattice at high temperatures. Since CH3NH3+ can deteriorate structural stability of MAPbI3 perovskites, it is possible to use molecular cation design and substitution as a mechanism to enhance the stability and remove this limitation. We here investigate the effect of replacing this cation with other organic cations (HCOHNH2PbI3 (FPbI3), CH3COHNH2PbI3 (AcPbI3), and NH2COHNH2PbI3 (UPbI3)) in order to enhance the performance of the perovskites, while also keeping the band gap energy (Eg) in an appropriate range for solar cell applications. The calculations are performed using the full potential linearized augmented plane wave method, providing lattice parameters and the formation energy of the proposed perovskites. Our results indicate that AcPbI3 perovskite outperforms the other structures in terms of various optical parameters, such as the absorption coefficient, optical conductivity, and reflectance. The optical and electronic band gaps of the AcPbI3 structure and its resonance form (Ac'PbI3) are found to be in agreement with each other, proposing them as optically tunable hybrid perovskites in emerging solar cells.