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• Theoretically examined the physical features of DPs Li 2 CuBiZ 6 (Z = Cl, Br, I). • Elastic properties are investigated for structural stability. • Electronic and optical properties for solar applications. • The dispersion of light is explained by ε 1 (ω). • Due to its higher Seebeck coefficient, Li 2 CuBiCl 6 possessed a larger power factor than Li 2 CuBiBr 6 and Li 2 CuBiI 6. Due to their potential applications for optoelectronic and thermoelectric devices, Li-based double perovskites (DPs) have been widely investigated. In current article, we theoretically examined the mechanical, optoelectronic and thermoelectric features of DPs Li 2 CuBiZ 6 (Z = Cl, Br, I). We employ the generalized gradient approximation (PBEsol) for examining the structural and elastic characteristics of these compounds, while the modified Becke-Johnson (mBJ) functional is used for obtaining an improved accord of the thermoelectric and electronic characteristics with experimental observations. For the stability of all DPs, the Born Criteria and formation energy are investigated. The cubic symmetry's elastic constants are examined to determine the difference between ductile and brittle nature, anisotropy, and Debye temperatures. The bandgaps are 2.0 eV, 1.7 eV, and 1.3 eV, for Li 2 CuBiCl 6 , Li 2 CuBiBr 6, and Li 2 CuBiI 6 , respectively, as determined by the mBJ potential. All DPs were also examined regarding optical absorption, refractive index, and dielectric constants for the energy range 0–10 eV, ensuring the absorption among visible regions. Furthermore, all DPs are appropriate candidates for thermoelectric applications due to the lower lattice thermal, higher Seebeck coefficient, thermal conductivity, and Figure of merit (ZT), which are all elucidated by Boltzmann classical theory. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct band gap semiconductor of Li based double perovskites halides A 2 LiInBr 6 (A = Rb, Cs) are explored in terms of density functional theory. • Structural and elastic investigation depict structural stability of A 2 LiInBr 6 in cubic phase. • The electronic band structures analysis show both materials are strong candidate for the fabrication of solar cell devices. • Optical parameters were calculated for the assurance of semiconductor behaviour. • Calculated thermoelectric parameters indicate that the both materials can be used even at elevated temperatures. We exhibit the investigation of structural, optical, thermoelectric, and electronic properties of A 2 LiInBr 6 (A = Rb, Cs) by applying density functional theory. The calculated bandgap of cubics structure using modified Becke and Johnson (mBJ) potential indicates that the bandgap reduces by replacing cations Rb to Cs. The calculated values appear in the visible energy range. Further, investigation of optical characteristics suggest that they might be used in solar cells. In addition, promising thermoelectric applications demand the small bandgap, which results from a high figure of merit for A 2 LiInBr 6. The computed small bandgap, high optical absorption, and maximum values of the figure of merit (ZT) stipulate Cs 2 LiInBr 6 applicable for solar absorbing cells and energy conversion applications. [ABSTRACT FROM AUTHOR]

• Double perovskites halides K 2 AgBiX 6 (X = Cl, Br) are executed in terms of density functional theory. • Structural and thermodynamic investigation depict structural stability of K 2 AgBiX 6 in cubic phase. • The electronic band structures and optical analysis show both halides are strong candidate for the fabrication of solar cell devices. • Calculated thermoelectric parameters indicate that the both halides can be used even at elevated temperatures. Lead-free double-perovskites (DPs) K 2 AgBiX 6 (X = Cl, Br) has been executed as well as examined by ab-initio computations for solar cell energy sources. Improved and latest Becke and Johnson potential (TB-mBJ) has been suggested to calculate optoelectronics characteristics. The lattice constants reported theoretical and computed values using Perdew-Burke-Ernzerhof's generalized-gradient-approximation (PBEsol-GGA) had been determined in good agreement. The calculated bandgap 2.3 eV (K 2 AgBiCl 6) and 1.5 eV (K 2 AgBiBr 6) disclosed their indirect nature, which showed that these are suitable potential candidates for visible light solar-cell (SC). Optical ranges explain the dielectric-constant, light absorption and reflection, and refractive index. The maximum absorption band has been noted within the wavelength of 620–310 nm. In addition, the BoltzTraP (BT) Code has been determined thermoelectric characteristics that result in higher value Seebeck coefficient and lower thermal conductivity. Hence, executed theoretical calculation proposed that examined material has potential application in renewable energy fields. [ABSTRACT FROM AUTHOR]

• DFT calculations are executed for halides double perovskites Cs 2 ScAgX 6 (X = I, Cl, Br). • Structural and elastic investigations represent stability of Cs 2 ScAgX 6 (X = I, Cl, Br) in cubic phase. • The band structures analysis show their indirect bandgap nature of Cs 2 ScAgX 6 (X = I, Cl, Br). • The computed band structures and optical parameters indicate potential solar cells devices applications. • Electronic thermal coefficients are probed and suggested studied halides as promising thermoelectric materials. As a possible suitor for application of solar cells and thermoelectric, halide based double perovskites has been developed due to their ecosystem stability, non-toxicity and noticeable performance. In current study, we have explored structural stability and elastic properties of Cs 2 ScAgX 6 (X = I, Cl, Br) in the cubic phase through tolerance factor and Born stability criteria calculations. Further, we present an extensive analysis of optical, electronic and electronic transport characteristics. An indirect semiconducting bandgap in the range of 1.9 eV and 1.55 eV is observed while analyzing electronic band structure and play vital role in solar cells applications. According to their bandgap values, maximal absorption in visible region is perceived, which reduces the bandgap when chlorine is substituted with bromine and iodine. Dielectric constants and other relevant parameters were produced by studying optical characteristics of Cs 2 ScAgX 6. Within the visible region, the maximum absorption of light has been recorded by investigating dielectric constant. Finally, thermoelectric properties are computed using the BoltzTraP package. The value of figure of merit, which is around 0.74 at 300 K, clearly suggests that these materials are also used as potential candidate for thermoelectric devices. [ABSTRACT FROM AUTHOR]

The toxicity and instability of lead-based perovskites have been replaced with newly investigated stable lead-free inorganic perovskites. The current study included the comprehensive analysis of electronic behavior, elastic, optical, and transport characteristics of lead-free inorganic double perovskites (DPs) Rb 2 KTlX 6 (X = Cl, Br) halides for possible uses. These physical characteristics were revealed using density functional theory (DFT) based Wien2k code. Using the energy optimization process, we have computed structural parameters comparable to existing data using generalized gradient approximation (PBEsol-GGA). In addition, the elastic parameters, formation energy (−1.94 eV and −1.39 eV), and tolerance factor (0.98 and 0.97) endorsed the cubic stability of both halides. Further, we employed modified Becke-Johnson (mBJ) potential to an accurate value of direct bandgaps of both halides reveal that changing the anions from Cl to Br leads to significant adjustment in the band gap, transitioning from the visible to the IR spectrum, with energy levels ranging from 2.08 to 1.2 eV. Our calculated results of optical parameters indicate that both halides with remarkable optoelectronic working due to low reflectivity, high optical absorption, and conductivity. The study reveals that electronic transport factors are associated with temperature due to small bandgap of the materials. The observed figure of merit near unity indicates the semiconducting behavior of these materials that can be useful in thermoelectric tools. • First-principle calculations of DPs Rb 2 KTlX 6 (X = Cl, Br). • Direct bandgap semiconductor. • Optical characteristics for optoelectronic devices. • Transport characteristics are discussed in details for thermoelectric devices. [ABSTRACT FROM AUTHOR]

Intense research work is underway for identifying materials with potential applications in energy storage and energy harvesting systems. The magnesium based scandium chalcogenides have recently emerged as potential candidates for Mg batteries owing to their high Mg ionic conductivity and low electron conduction. At the same time, their band gaps are capable of absorbing electromagnetic radiations in visible to UV range; making them suitable for solar cell applications. In order to analyze the application of MgSc 2 X 4 (X = S, Se) compounds in energy devices, in this work we employ density functional theory calculations using the full potential linear augmented plane-wave method for examining their optoelectronic and thermoelectric properties. For the structural properties, the generalized gradient approximation functional designed for solids (PBEsol-GGA) has been used, while modified Becke and Johnson (mBJ) potential functional is used for computing the optoelectronic and transport properties. Our calculated optical properties indicate that these materials can find applications in solar cells. Moreover, the electronic transport properties computed using Boltzmann transport equation suggest carrier concentrations in MgSc 2 S 4 to MgSc 2 Se 4 spinels can be tuned for making them suitable for metal ion batteries. [ABSTRACT FROM AUTHOR]

Using the full-potential linearized augmented plane wave plus local orbitals method within the frame work of density functional theory, the Sc-based double halide perovskites K 2 ScAgZ 6 (Z = Cl, Br, I) are investigated for determining their physical properties. To investigate the structural and thermodynamic stability of these Sc-based double halide perovskites we calculate tolerance factor, formation energy, and phonon dispersion curve using GGA-PBEsol approximation. The calculated values of lattice parameters using GGA-PBEsol are found to be consistent with the available data. Subsequently, the Tran-Blaha modified Becke-Johnson (mBJ-LDA) potential is used for electronic properties. Implementation of TB-mBJ potential is clearly shows that K 2 ScAgZ 6 have indirect bandgap, which is consistent with the literature. To evaluate these double perovskites and reveal their potential use in optical devices, several optical parameters are computed for an incident photon energy range of 0–8 eV. The BoltzTraP code is also employed to investigate temperature dependent electrical characteristic of these compounds in the temperature range of 200–600 K. Investigated halide double-perovskites have been shown to display excellent physical properties for solar cells and renewable energy device applications. • In the cubic phase double perovskites are structurally and thermodynamically stable. • The calculated indirect bandgaps for K 2 ScAgCl 6 , K 2 ScAgBr 6 , and K 2 ScAgI 6 are 2.0, 1.85, and 1.65 eV. • These are suitable materials for solar cell devices due to their greatest least reflection, absorption, and optical loss in the visible area. [ABSTRACT FROM AUTHOR]

• Rb 2 YInX 6 (X = Cl, Br, I) double perovskites have highly structural stability determined from volume-energy optimization and negative formation energy. • Direct bandgap in the range of 3.05–2.20 eV make them more attractive materials. • The Rb 2 YInBr 6 have large value of figure of merit which means it has largest conversion efficiency to convert thermal energy into electrical energy. The double perovskite-based materials have attracted considerable attention of scientists owing to their potential applications in optoelectronic and transport properties. Here, we report the optoelectronic and transport properties of Rb 2 YInX 6 (X = Cl, Br, I) double perovskites by DFT computations. By computing tolerance factor (t G) , enthalpy of formation (ΔH f) and lattice constant (a o), the thermodynamic and structural stabilities are verified. The energy bandgap computations for Rb 2 YInX 6 gives direct bandgap having values 3.05, 2.60 and 2.20 eV for Cl, Br and I based compositions respectively. Optical absorption calculations executed within the energy range of 2–8 eV which validate its use in optoelectronic applications like solar cells. Using semi classical Boltzmann theory computed values of ZT illustrates that Rb 2 YInBr 6 is fairly good candidate for transport applications. These compounds may attain consideration in optoelectronic and thermoelectric properties. [ABSTRACT FROM AUTHOR]

• The structural, electronic, and optical features of Cu 2 ZnSn(S x Te 1-x) 4 alloys are examined. • Kesterite structure is more favorable and sustainable for these materials than stannite one. • Absorption coefficient spectra are altered with the change of Te composition in these systems. • A birefringence occurred in Cu 2 ZnSn(S x Te 1-x) 4 alloys with the variation of composition x. • CZTS and CZTS 0.75 Te 0.25 could be promising materials as absorber layers of thin film solar cells. Cu 2 ZnSnS 4 (CZTS), a quaternary material formed of Earth-abundant elements, is promising in thin-film solar cell devices, as absorbing layer. The high efficiency of solar energy conversion (>12%) recorded in chalcogen-doped Cu 2 ZnSnS 4 renders it an attractive material for the analysis of the structural stability, electronic band structures, and optical characteristics of Cu 2 ZnSn(S x Te 1-x) 4 alloys (0 ≤ x ≤ 1) by first-principles calculations. By employing full-potential linearized augmented plane-wave (FP-LAPW) methodology, the acquired results indicate that CZTS and Cu 2 ZnSnTe 4 (CZTTe) parent compounds possess wide and narrow direct band gaps, respectively. The optical characteristics of Cu 2 ZnSn(S x Te 1-x) 4 alloys and their bulk counterparts were computed in terms of the complex dielectric function, which allows the examination of the optical absorption, reflectivity, and refractive index of these ultimate alloys. It is inferred that the S/Te compositional ratio in Cu 2 ZnSn(S x Te 1-x) 4 has a significant influence on the optical absorption of electromagnetic radiation in the visible to the infrared (IR) regimes. Our results indicate that the increase of Te concentration leads to a red shift of the major feature peaks in the optical absorption spectra. Because of their direct band gap and remarkable optical absorption, Cu 2 ZnSn(S x Te 1-x) 4 alloys with S/Te compositional ratios under 0.5 could be useful materials in thin-film solar cell devices, as absorbing layers. This theoretical report is expected to provide relevant information for future experimental works involving the design of novel solar cell materials based on CZTST systems. [ABSTRACT FROM AUTHOR]

Double perovskite halides are a potential candidate for the applications of the solar cell, photovoltaic and thermoelectric, due to their non-toxicity and environmental stability. The density functional theory (DFT) calculation investigates the details physical properties of halides Rb 2 ScAgX 6 (X = Cl, Br, I) that can be useful for applications like thermoelectric and solar cells. The structural and thermodynamics stability is endorsed by the formation energy, tolerance factor, and Born stability criteria. The calculated indirect band gaps of 1.95 eV, 1.85, and 1.60 eV for Rb 2 ScAgCl 6 , Rb 2 ScAgBr 6 , and Rb 2 ScAgI 6 respectively, ensure the light absorption in the region of visible range. Therefore, all studied halides are widely used in optoelectronic devices like solar cells. In addition, thermoelectric properties are examined through thermal conductivity, electrical conductivity, and the Seebeck coefficient. ZT values of 0.74, 0.71, and 0.72 for Rb 2 ScAgI 6 , Rb 2 ScAgBr 6 , and Rb 2 ScAgCl 6 double perovskites are recorded, which spotlight their significance for the applications of thermoelectric. [ABSTRACT FROM AUTHOR]