Analysis of optoelectronic and trasnport properties of magnesium based MgSc2X4 (X=S,Se) spinels for solar cell and energy storage device applications

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 MgSc₂X₄(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 MgSc₂S₄ to MgSc₂Se₄ spinels can be tuned for making them suitable for metal ion batteries.     

Sol-gel synthesis,characterization, and supercapacitor applications of MCo2O4 (M = Ni,Mn, Cu,Zn) cobaltite spinels

High performance MCo₂O₄spinels (M = Ni, Mn, Cu, Zn) were synthesized by the sol gel method (citrate) and their capacitive behavior was investigated in alkaline electrolyte. Their structural, morphological, functional groups and textural properties were characterized by TG/DSC, XRD, SEM, FTIR, EDS and BET. The capacitive properties of spinel MCo₂O₄ samples were thoroughly investigated in 1?M KOH aqueous electrolyte using cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results revealed high stability of the samples and excellent electrochemical reversibility, and exhibited specific capacity depending on the nature of the transition metal ion M. A high specific capacitance of 285?F?g^?1 was measured for CuCo₂O₄ and a low capacitance of 158?F?g^?1 for ZnCo₂O₄.In addition, MCo₂O₄ spinels displayed good stability during long-term cycles with a cycling efficiency which exceeds75% after 1000 cycles. The obtained results classified MCo₂O₄ cobaltite spinels as most promising materials for their application in super capacitors.     

Enhanced thermoelectric and optical response of Ag substituted Cu2O compositions for advanced applications

Cu₂O based semiconductor materials are promising candidates for modern electronic devices due to have excellent electronic and optical properties. In this work, pure and Ag doped Cu₂O structures were simulated using density functional theory in the framework of wien2k code with generalized-gradient-approximation under full potential linearized augmented plane wave approach. Experimentally, pure and Ag doped Cu₂O uniform thin films were successfully fabricated. The morphology and elemental compositions of thin films were investigated using field emission scanning electron microscopy and energy dispersive x-rays spectroscopy, respectively. X-ray diffraction analysis exhibited cubic phase having space-group 224-Pn-3m in all synthesized thin films. Total density of states spectra for Ag containing compositions present overlapping of states at Fermi level. Thermoelectric properties show a significant variation in various parameters with the change in temperature and Ag content in structure. The see-beck coefficient was observed to vary from 0.0002 to 0.00035 Vk⁻¹ for pure and Ag doped Cu₂O compositions. The optical parameters like extinction and absorption curves attains maximum values at higher photon energies. The refractive index presents an enhanced transmittance power with the increment in photon energy. The band gap was found to reduce from 2.33 eV to 1.99 eV with Ag doping attributed to the sharp increase in optical conductivity.     

Half metallic ferroamgnetism,and transport properties of vacancy ordered double perovskites Rb2(Os/Ir)X6 (X = Cl,Br) for spintronic applications

The defected double perovskites, being non-toxic, stable, and capable to exhibit both spin-up (↑) and spin-down (↓) polarizations, are attractive for spintronic devices. In the present article, the role of 5d-electrons of Os and Ir to control the magnetic characteristics of Rb₂(Os/Ir)Cl/Br₆ is addressed. The structural and magnetic characteristics are investigated using PBEsol-mBJ functional, while thermoelectric behaviors are studied using BoltzTrap code. The computed tolerance factors (0.95/0.98, 0.94/0.96) and formation energies (?2.0/-1.65eV, ?1.70/-1.10eV) confirm the structural and thermodynamic stabilities, respectively. The examination of band structures and density of states have revealed half-metallic ferromagnetic nature, which is further discussed in terms of double exchange model, exchange constants and exchange energies. The presented calculations indicate that underlying hybridization process, exchange energy, and crystal field energy induce ferromagnetism due to electron spin. Furthermore, thermal, and electrical conductivities, power factor, and Seebeck coefficients are computed and discussed to understand the thermoelectric applications.     

Systematic study of optoelectronic and transport properties of cesium lead halide (Cs2PbX6; X=Cl,Br, I) double perovskites for solar cell applications

A systematic density functional theory investigation of Cs₂PbX₆ (X = Cl, Br, I) double perovskites is presented. The lattice constants are computed after structure optimization and using Birch-Murnaghan equations, which agree to the experimental literature. The mechanical stability conditions satisfy Born criteria, and the ductile nature is evidenced by the calculated Poisson's (v) and Pugh's ratios (B₀/G) because all three double perovskites exhibit values higher than the respective critical values v = 0.26 and B₀/G = 1.75. A detailed study of the optoelectronic properties reveals these double perovskites as promising candidates for future optical devices due to their direct band gaps (within 0.45–2.54 eV) and large absorption coefficients 5.95 × 10⁵ cm⁻¹, which are suitable for solar cell applications. ZT calculations demonstrate minute variations within 200–800 K and computed parameter values are quite favorable for thermoelectric applications of these materials in the future. A p-type semiconducting nature is predicted by the computed thermoelectric properties. Additionally, computed refractive indices show Cs₂PbBr₆ and Cs₂PbI₆ exhibiting super-luminescent properties in the UV range. Therefore, the studied double perovskites provide further interest for future energy conversion and photonic based technologies.     

Influence of the selenization time on the properties of (Na0.1Cu0.9)2ZnSn(S,Se)4 thin films and their photovoltaic solar cells

(Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin films with a single kesterite phase were synthesized using a sol-gel spin-coating method accompanied by rapid post-annealing. In this study, we investigated the effect of selenization time on the crystal quality and photoelectric performance of the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ films. It was found that the crystallinity and morphology of the films was enhanced, and some of bigger Se substituted for the S site in (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ with increasing the selenization time. The bandgap of the film can be regulated from 1.04 eV to 0.99 eV by varying the selenization time. In addition, all films showed p-type conductive characteristics, and films with optimal electrical performance could be obtained by optimizing the selenization time. Finally, the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin film with the best crystal quality and optical-electrical characteristics was obtained at an optimized selenization time of 15 min. A high power conversion efficiency (PCE) of 3.92% was obtained for the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ device, which is 42% higher compared to that of the undoped Cu₂ZnSn(S,Se)₄ (CZTSSe) device.     

Preparation and characterization of Ag2ZnSn(S,Se)4 and its application in improvement of power conversion efficiency of Cu2ZnSn(S,Se)4-based solar cells

We fabricated high-quality n-type Ag₂ZnSnSe₄ (AZTSe) film with kesterite structure by using a simple solution method. A Cu₂ZnSnSe₄ (CZTSe)/AZTSe-based solar cell was designed and prepared by inserting AZTSe layer between CZTSe and CdS of the traditional CZTSe-based solar cell. Compared with the traditional device, an increase from 337 to 432 mV in open circuit voltage (V_oc) and an accompanying rise from 3.40% to 4.72% in power conversion efficiency (PCE) were observed. To well understand the PCE improvement of the CZTSe/AZTSe-based solar cells, we calculated the band alignments of CZTSe/AZTSe and CZTSe/CdS heterojunctions using first-principles calculations, demonstrating that the CZTSe/AZTSe and CZTSe/CdS interfaces have type-II and type-I band alignments, respectively. Moreover, the band offset of AZTSe/CdS is lager than the one of CZTSe/CdS. Combined with the calculation results, the mechanism of influence of the AZTSe on the PCE improvement is discussed in detail. Our conclusions show that the addition of the AZTSe layer is a potentially applicable method to obtain CZTSe-based solar cells with higher V_oc and PCE.     

The novel material based on strandberg-type hybrid complex (C6H10N2)2[Co(H2O)4P2Mo5O23].6H2O: Experimental and simulations investigation on electronic,optical, and magnetocaloric properties

The hybrid Strandberg complex materials have attracted intensive interest due to their multifunctional properties. In this work, we report the electronic, optical, and magnetocaloric properties of the novel material (C₆H₁₀N₂)₂[Co(H₂O)₄P₂Mo₅O₂₃].6H₂O. First principle calculations based on the density functional theory (DFT) have been performed using full-potential linearized augmented plane waves (FP-LAPW). The crystals of (C₆H₁₀N₂)₂[Co(H₂O)₄P₂Mo₅O₂₃].6H₂O with triclinic structure were characterized by X-ray powder diffraction (XRD). The profiles of the density of states (DOS), the optical spectra including the real and imaginary part of the dielectric function, and the measured magnetocaloric properties were presented and analyzed in detail. The results found are in agreement with experimental measurements. As pertinent results, the compound presents a high absorption coefficient in the visible range. A systematic analysis of the experimental and theoretical results shows a good bandgap, a high optical property, and a low magnetocaloric effect which reveals promising original material in optoelectronic, and photovoltaic applications.     

Thermal,optical, dielectric and electrical transport properties of nano-structured Se95-xIn5Prx (x = 2, 4, and 6) glassy alloys

In the present study, Se_95-xIn₅Pr_x (x = 2, 4, and 6) alloys were prepared using the melt quench technique. X-ray diffraction (XRD) and Raman spectroscopy reveal that the glassy matrix of each sample consists of crystalline entities identified as a mixed phase of indium selenide (HCP) and praseodymium selenide (FCC). TEM images show that the crystalline entities are nanorods stuck to nanoparticles. The thermal stability and optical band gap (direct) decrease (1.974 eV to 1.425 eV) with Pr content. The dielectric constant and loss are maximums for x = 4 at any frequency and temperature (30°C-60 °C). AC conductivity follows the correlated barrier hopping (CBH) model (frequency exponent $s<1\text{,}$ and decreases with temperature) with non-intimate valence alteration pairs (NVPA) for x = 2 and 6, and intimate valence alteration pairs (IVPA) for x = 4. AC activation energy decreases with Pr concentration at all frequencies in the study range.     

Synthesis and investigation of environmental protection and earth-abundant kesterite Cu2MgxZn1-xSn(S,Se)4 thin films for solar cells

We have synthesized Cu₂Mg_xZn_1–xSn(S,Se)₄ (0?≤?x?≤?0.6) thin films by a facile sol-gel method, and studied the influence of Mg concentration on the crystal structure, surface morphology and photoelectric performance of Cu₂Mg_xZn_1–xSn(S,Se)₄ thin films systematically. It was shown that the smaller Zn²⁺ in Kesterite phase Cu₂ZnSn(S,Se)₄ will be replaced by larger Mg²⁺, forming uniform pure phase Cu₂Mg_xZn_1–xSn(S,Se)₄. The band gap of Cu₂Mg_xZn_1–xSn(S,Se)₄ films can be adjusted from 1.12 to 0.88?eV as the x value changes from 0 to 0.6. Furthermore, the Cu₂Mg_xZn_1–xSn(S,Se)₄ thin films with large grain size, smooth surface and less grain boundaries was obtained at an optimized condition of x?=?0.2. The carrier concentration of Cu₂Mg_xZn_1–xSn(S,Se)₄ thin film reaches the maximum 6.47?×?10¹⁸ cm^?3 at x?=?0.2, which is a potential material to be the absorption layer of high efficiency solar cells.     

Thermal expansion coefficient and relaxation parameters of glasses in the system GaX2-GeX2-Sb2X3 (X = S, Se)

The concentration behavior of the thermal expansion coefficient of glasses in the system GaX₂-GeX₂-Sb₂X₃ (X = S, Se) has been studied in two sections. Parameters characterizing the relaxation properties of the glasses have been calculated on the basis of the Tool-Narayanaswamy theory from experimental temperature dependences of the thermal expansion coefficient in the softening range. Temperature dependences of the viscosity have been calculated under the assumption of equal free activation energies for the relaxation and viscous flow.     

Spray-deposited kesterite Cu2ZnSnS4 (CZTS): Optical,structural, and electrical investigations for solar cell applications

Kesterite Cu₂ZnSnS₄ (CZTS)-based solar devices have become a popular alternative to copper indium gallium selenide (CIGS) due to its outstanding properties such as high efficiency, non-toxicity, cost-effectiveness, suitable optoelectrical properties, and earth-abundancy. In this study, we directly fabricated CZTS films via a single-step spray pyrolysis technique, in contrast to conventional techniques where post sulfurization is required. The spray deposited CZTS films are investigated for their optical, structural, and electrical properties. The X-ray diffraction (XRD) and Raman analysis study revealed the synthesis of the phase-pure kesterite CZTS films without impurity phases. Large crystallites of CZTS are obtained at a deposition temperature of 400 °C, exhibiting a porous granular morphology with different grain sizes upon temperature variation. The size-dependent optical properties revealed that the CZTS films exhibited admirable visible light absorption of 10⁵ cm^?1 and an electronic bandgap ranging between 1.42 and 1.58 eV. The minimum dielectric loss obtained for optimized CZTS due to fewer intrinsic defects confirmed the materials’ applicability. Thus, the study provides a simple, viable route to fabricate CZTS without post-treatment to build affordable solar cells.     

Elastic and electronic properties of XB2 (X=V,Nb, Ta,Cr, Mo,and W) with AlB2 structure from first principles calculations

The crystal structure, electronic properties, mechanical properties, and anisotropy of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) were calculated by first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The results are in good agreement with available theoretical and experimental values. The calculated cohesive energy and formation enthalpy indicate that they are thermodynamically stable structures. The elastic constants satisfy all of the mechanical stability criteria. The mechanical moduli were predicted by the Voigt–Reuss–Hill approximation. The mechanical anisotropy was indicated by the surface constructions of Young's moduli, and the results show that anisotropy of WB₂ is stronger than others. The electronic structure indicates that the bonding behaviors of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) are the combinations of covalent and metallic bonds. The hardness of the borides was also evaluated, and the result reveals that TaB₂ is the hardest compound among them.     

Density functional theory study on lithium bis[1,2-benzenediolato(2-)-O,O′] borate and its derivatives: electronic structures, energies, and molecular properties

Theoretical studies on electrolyte salts, lithium bis[1,2-benzenediolato(2-)-O,O′] borate (LBBB) and its derivatives, lithium bis[3-fluoro-1,2-benzenediolato(2-)-O,O′]borate (1FLBBB), and lithium bis[tetrafluoro-1,2-benzenediolato(2-)-O,O′] borate(4FLBBB) are carried out using density functional theory (DFT) method and B3LYP theory level for the first time. Bidentate structures involving two oxygen atoms are preferred. The GIAO–DFT results for all molecules suggest that the corresponding RB3LYP/6-31++G(2df,2p) geometries can be deemed reasonably good representations of the geometries of relatively free molecules in solution. Based on these conformations, a linear correlation was observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that inorganic fluorine-containing anions are more resistant against oxidation than their organic counterparts. The correlations were also observed between ionic conductivity and binding energy, solubility and anion polarizability_, thermal stability and the energy difference between E_LUMO and E_HOMO. Wave function analyses have been performed by natural bond orbital (NBO) method to further investigate the cation–anion interactions.     

Thermophysical properties of (La0.25Sm0.25Gd0.25Yb0.25)2Ce2+xO7+2x(x=0.1, 0.2, and 0.3) high entropy oxides

A series of high-entropy oxides (La_0.25Sm_0.25Gd_0.25Yb_0.25)₂Ce_2+xO_7+2x were synthesised adopting a improved sol-gel technique and fritting method. The crystal-lattice, microstructure, elemental constitution, and thermal-physical performances were studied. The results showed that the synthesised high-entropy oxides have a single-fluorite lattice structure. The bulk specimen exhibits a compact microstructure, and clear grain boundaries. The thermal conductivities of the obtained high-entropy oxides are lower than those of CeO₂ and 7YSZ due to lattice strains and numerous oxygen vacancies. The obtained high-entropy oxides have greater thermal expansion coefficients than 7YSZ. The thermal conductivity and expansion coefficient are elevated because of the addition of excess CeO₂. The synthesised high-entropy oxides also exhibit outstanding lattice steadiness up to 1200 °C.     

Effect of the alkali metal (Li,Na, K) substitution on the geometric,electronic and optical properties of the smallest diamondoid: First principles calculations

In this study we employed the B3LYP/6-311++G(d,p) method combined with the CIS/6-311++G(d,p) calculation to investigate the effects of the type and the number of alkali metal atoms(Li, Na, K) on the geometric, electronic, and optical properties of alkali metals substituted into adamantanes. Substituting alkali metal(Li, Na, K)atoms caused significant changes in the electronic and optical properties of adamantane. The Ad-1Li, Ad-1Na,and Ad-1K structures showed a dramatically decreased energy gap and ionization potential, while adding more alkali metal atoms slightly decreased these properties. Substituting more alkali metals led to a shift in the maximum absorption wavelength from the visible to the infrared region, depending on the type of alkali metal atom substituted. The magnitude of shift occurred in the following order: Li b Na b K. These characteristics suggest the possibility of tunable electronic structures of this material for optoelectronic device applications.     

Structure and enhanced thermoelectric properties of InGaO3(ZnO)m (m=1, 2, 3, 4, and 5) ceramics

InGaO₃(ZnO)_m (m = 1, 2, 3, 4, and 5) ceramics are a series of n-type oxide thermoelectric materials with layered structures and low thermal conductivities. Herein, InGaO₃(ZnO)_m (m = 1, 2, 3, 4, and 5) ceramics were fabricated by spark plasma sintering (SPS). Two different trends in the thermoelectric properties of the InGaO₃(ZnO)_m (m = 1, 2, 3, 4, and 5) ceramics were observed depending on the odevity of the m value. The InGaO₃(ZnO) sample exhibited a relatively high electrical conductivity and was therefore selected for vacuum annealing to further improve the electrical transport performance. Oxygen vacancy defects were introduced to the matrix during the annealing procedure, which improved the thermoelectric performance. A maximum ZT of 0.45 was obtained at 973 K for the InGaO₃(ZnO) sample with a 96 h vacuum annealing treatment, which is 30 times higher than that of the pristine sample.     

Investigation of bulk hybrid heterojunction solar cells based on Cu(In,Ga)Se2 nanocrystals

This work presents the systematic studies of bulk hybrid heterojunction solar cells based on Cu(In, Ga)Se₂ (CIGS) nanocrystals (NCs) embedded in poly(3-hexylthiophene) matrix. The CIGS NCs of approximately 17 nm in diameter were homogeneously blended with P3HT layer to form an active layer of a photovoltaic device. The blend ratios of CIGS NCs to P3HT, solvent effects on thin film morphologies, interface between P3HT/CIGS NCs and post-production annealing of devices were investigated, and the best performance of photovoltaic devices was measured under AM 1.5 simulated solar illumination (100 mW/cm²).     

A First-Principles Investigation on the Structural,Optoelectronic, and Thermoelectric Properties of Pyrochlore Oxides (La2Tm2O7 (Tm = Hf,Zr)) for Energy Applications

A first-principles calculation based on DFT investigations on the structural, optoelectronic, and thermoelectric characteristics of the newly designed pyrochlore oxides La₂Tm₂O₇ (Tm = Hf, Zr) is presented in this study. The main quest of the researchers working in the field of renewable energy is to manufacture suitable materials for commercial applications such as thermoelectric and optoelectronic devices. From the calculated structural properties, it is evident that La₂Hf₂O₇ is more stable compared to La₂Zr₂O₇. La₂Hf₂O₇ and La₂Zr₂O₇ are direct bandgap materials having energy bandgaps of 4.45 and 4.40 eV, respectively. No evidence regarding magnetic moment is obtained from the spectra of TDOS, as a similar overall profile for both spin channels can be noted. In the spectra of ε2(ω), it is evident that these materials absorb maximum photons in the UV region and are potential candidates for photovoltaic device applications. La₂Tm₂O₇ (Tm = Hf, Zr) are also promising candidates for thermoelectric device applications, as these p-type materials possess ZT values of approximately 1, which is the primary criterion for efficient thermoelectric materials.