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Transition-metal sulfide SnS2 has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS2 lead to inferior cycle stability as well as rate performance. In this work, FeS2 was in situ introduced to synchronously grow with SnS2 on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS2/FeS2/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na+ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials' structural stability. SnS2/FeS2/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g-1 at the current density of 0.1 A g-1, and 541.2 mA h g-1 at the current density of 1 A g-1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS2 or FeS2. TDOS calculation further confirms that the binding of FeS2/SnS2-Na is more stable than FeS2 and SnS2 alone. The superior electrochemical performance of the SnS2/FeS2/rGO composite material makes it a promising candidate for sodium storage.

Theoretical limit (or detailed balance limit) of photovoltaic performances of single-junction solar cell was estimated under consideration of radiative recombination, where the solar cell was assumed as blackbody with temperature (T) of 298.15 K. The detailed balance limit of the perovskite solar cell is furthermore calculated under considerations of not only radiative recombination but also Auger recombination. It is revealed that open-circuit voltage (VOC) is primarily reduced with increasing the intrinsic density (ni) and Auger recombination coefficient (Cp), thus decreasing the conversion efficiency (η). Under the Eg of 1.55 eV and ni of 1 × 107 cm−3, the η of perovskite solar cell is reduced from 31.41% (without Auger recombination consideration) to 28.92% with the increased Cp to 1 × 10−29 cm6.s−1. According to the result, the Cp should be lower than 1 × 10−31 cm6.s−1 to avoid the impact of Auger recombination for the improved performances of perovskite solar cells, where it is suggested that the Cp can be reduced through band-structure engineering and alloying with other halide perovskites, thereby providing the avenues for material design. Furthermore, the effect of Shockley-Read-Hall recombination in the perovskite solar cell on its efficiency limit is discussed.

The lattice dynamics of CsSnX3 (X = Cl, Br, and I) and CsPbI3, which are low-thermal-conductivity materials, are investigated using first-principles phonon calculations. Because of the strong lattice anharmonicity and the accompanying instability of high-temperature cubic phases, the self-consistent phonon theory, which can incorporate the effect of lattice anharmonicity at a mean-field level, is applied in this study. The calculated lattice thermal conductivity reproduced a low thermal conductivity, as shown experimentally, owing to the short phonon lifetime due to the incoherent scattering contribution of Cs atoms. The halogen ion dependence on thermal conductivity reveals that CsSnCl3 exhibits an anomalous lattice thermal conductivity that is as low as that of CsSnBr3. This indicates that the lattice dynamics cannot be explained merely in terms of the atomic mass of the compounds. The low thermal conductivity of CsSnCl3 is caused by the exceptionally short phonon lifetime; further, a bonding analysis suggests that covalent bonding contributes significantly to the unusual anharmonicity of CsSnCl3.

Research on tin-lead (SnPb) perovskite solar cells (PSCs) has gained popularity in recent years because of their low band gap, which could be applied to tandem solar cells. However, most of the work is based on inverted PSCs using PEDOT:PSS as the hole-transport layer as normal-structure PSCs show lower efficiency. In this work, the reason behind the low efficiency of normal-structure SnPb PSCs is elucidated and surface passivation has been tested as a method to overcome the problem. In the case of normal PSCs, at the interface between the titania layer and SnPb perovskite, there are many carrier traps observed originating from Ti-O-Sn bonds. In order to avoid the direct contact between titania and the SnPb perovskite layer, the titania surface is passivated with carboxylic acid C60 resulting in an efficiency increase from 5.14 to 7.91%. This will provide a direction of enhancing the efficiency of the normal-structure SnPb PSCs through heterojunction engineering.

Inorganic CsSnI3 based perovskite crystals are interesting thermoelectric materials, owing to their unusual electronic properties. Here we report the thermoelectric power performance of a solution-coated CsSnI3 thin film from the viewpoint of carrier concentration optimizations. It was found that the carrier concentration can be changed by altering the aging time of the precursor solution. X-ray photoelectron spectroscopy analysis showed that the concentration of metallic Sn4+ increased as the solution aging time increased. This made possible to explore the relationship between carrier concentration and thermoelectric power factor. After controlling Sn4+ concentrations, we report a power factor of 145.10 μW m−1 K−2 , along with electrical conductivity 106 S/cm and Seebeck coefficient of 117 μV/K, measured at room temperature.

Transition-metal sulfide SnS

Recently, Sn perovskite solar cell (Sn PVK PV) are attracting attention. However, the efficiency was still lower than that of Pb perovskite solar cells. Recently, the Sn PVK PVs with efficiency higher than 10% have been reported from several research groups. The crystal defects include the presence of Sn4+, Sn2+ defect, I- defect, the presence of Sn0, the interstitial I- and so on. In order to decrease these defect densities, we have proposed some processes such as addition of Ge2+ ion, introduction of ethylammonium cation into A site, and surface passivation of perovskite grain boundary with diaminoethane dilute solution. Our results on efficiency enhancement (13%) is explained by the conduction and valence band energy level against carrier trap depth. In addition, an inverted SnPb perovskite solar cells with 23.3% efficiency is discussed from the view point of optimization of energy alignment.

Cellulose films regenerated from aqueous alkali-urea solution possess different properties depending on coagulation conditions. However, the correlation between coagulant species and properties of regenerated cellulose (RC) films has not been clarified yet. In this study, RC films were prepared from cellulose nanofiber (CNF) and microcrystalline cellulose (MCC) under several coagulation conditions. Cellulose dissolved in aqueous LiOH/urea solution was regenerated using various solvents at ambient temperature to investigate the effects of their polarity on the properties of RC film. The crystal structure, mechanical properties, and surface morphology of prepared RC films were analyzed using X-ray diffraction (XRD), tensile tester, and atomic probe microscopy (AFM), respectively. It is revealed that the preferential orientation of (110) and (020) crystal planes, which are formed by intra- and inter-hydrogen bonding in cellulose crystal regions, changed depending on coagulant species. Furthermore, we found out that tensile strength, elongation at break, and crystal structure properties of RC film strongly correlate to the dielectric constant of solvents used for coagulation process. This work, therefore, would be able to provide an indicator to control the properties of RC film depending on its application and to develop the detailed research on controlling the crystal structure of cellulose.

In the composition of Q0.1(FA0.75MA0.25)0.9SnI3, Q is replaced with Na+, K+, Cs+, ethylammonium+ (EA+), and butylammonium+ (BA+), respectively, and the relationship between actually measured lattice strain and photovoltaic performances is discussed. The lattice strain evaluated by the Williamson-hall plot of X-ray diffraction data decreased as the tolerance factor was close to one. The efficiency of the Sn-perovskite solar cell was enhanced as the lattice strain decreased. Among them, EA0.1(FA0.75MA0.25)0.9SnI3 having lowest lattice strain gave the best result of 5.41%. Because the carrier mobility increased with a decrease in the lattice strain, these lattice strains would disturb carrier mobility and decrease the solar cell efficiency. Finally, the results that the efficiency of the SnGe-perovskite solar cells was gradually enhanced from 6.42 to 7.60% during storage, was explained by the lattice strain relaxation during the storage.

The efficiency of Sn-perovskite solar (Sn-PVK) cells was enhanced by adding 1% Samarium iodide (SmI2). Increase in Jsc and FF is associated with the enhancement of efficiency and and explained by l...

This study uses first-principles calculations to investigate the effect of hydrogen on the chemical driving force of the transformation of iron from the face centered cubic (FCC) to hexagonal close packed (HCP) phase. The minimum energy path from FCC to HCP phases shows that FCC becomes stable with increasing hydrogen content. Furthermore, the energy difference between the FCC and HCP phases is observed to be smaller in Fe2H than in Fe throughout the temperature region. These results clearly explain the observed anomalous suppression of the martensitic transformation in the hydrogen-charged steel.

The reaction selectivity of an electrode catalyst can be modulated by regulating its crystal structure, and the modified electrode may show different CO2 reduction selectivity from that of its constituent metal. In this study, we investigated the mechanisms of the electrochemical CO2 reduction on an electrodeposited Cu3Sn alloy by experimental and theoretical analyses. The electrodeposited Cu3Sn alloy electrode showed selectivity for CO production at all the applied potentials, and HCOOH production increased with an increase in the applied potential. In particular, hydrocarbon generation was well suppressed on Cu3Sn(002). To understand this selectivity change in electrochemical CO2 reduction, we conducted density functional theory calculations for the reaction on the Cu3Sn(002) surface. According to the theoretical analysis, the Cu sites in Cu3Sn(002) contributed more to the stabilization of H*, COOH*, and CO* as compared with the Sn sites. Furthermore, the results indicated that Cu3Sn(002) decreased the ...

The effects of Mn, Cr, and Ni addition on the hydrogen diffusion behavior in BCC, FCC, and HCP Fe was investigated by means of first-principles calculations. Diffusion coefficients were estimated quantitatively from the migration energy calculated by the nudged elastic band method and the vibrational energy at every stable and metastable site. The addition of Mn, Cr, and Ni to a BCC lattice has a blocking effect on hydrogen diffusion and decreases the diffusion coefficient of hydrogen. Crystal orbital Hamilton population (COHP) analysis revealed that the weakened bonding between the added element and hydrogen is the origin of the blocking effect. On the other hand, the addition of Mn, Cr, and Ni to FCC and HCP lattices resulted in the formation of hydrogen trap sites. In the FCC case, the diffusion coefficients of Fe31MnH, Fe31CrH, and Fe32H, showed similar values, while that of Fe31NiH was lower. In the HCP case, the diffusion coefficients of the three additional elements showed a decreasing trend. Based on the results of the COHP analysis, we conclude that the octahedral interstitial sites around the additional elements become trap sites in FCC and HCP Fe due to the strengthened bonding between Fe and H.

This is a report on Pb free perovskite solar cells. Direction to enhancing efficiency for Sn-perovskite solar cells are discussed. In order to decrease carrier density and defect density in Sn-perovskite layers, Ge ion doping, surface and grain boundary passivation, decrease in lattice strain, and band alignment are proved to be effective. Ge doped Sn-perovskite solar cells with 13% efficiency is reported.

Research on tin-lead (SnPb) perovskite solar cells (PSCs) has gained popularity in recent years because of their low band gap, which could be applied to tandem solar cells. However, most of the work is based on inverted PSCs using PEDOT:PSS as the hole-transport layer as normal-structure PSCs show lower efficiency. In this work, the reason behind the low efficiency of normal-structure SnPb PSCs is elucidated and surface passivation has been tested as a method to overcome the problem. In the case of normal PSCs, at the interface between the titania layer and SnPb perovskite, there are many carrier traps observed originating from Ti-O-Sn bonds. In order to avoid the direct contact between titania and the SnPb perovskite layer, the titania surface is passivated with carboxylic acid C

The hydrogen diffusion behavior in BCC, FCC, and HCP iron has been investigated by means of first-principles calculations. Diffusion coefficients were estimated quantitatively from the migration energy derived by the Nudged elastic band method, and phonon calculations including the vibrations of all atoms at every stable and metastable site. Our calculations on the BCC structure show good agreement with those in the previous report. In the FCC structure as well, the calculated diffusion coefficients are in good agreement with experimental data. Our results suggest that the consideration of the antiferromagnetic state in FCC is important for the reproduction of experimental results. For the HCP structure, although there was a lack of systematic experimental results, our calculations predict that the diffusion coefficient is smaller than that in the case of the FCC sample. In the HCP lattice, there are two diffusion paths: one parallel to the c-axis and the other in the c-plane. The direction and the diffusion coefficient can be controlled by the tuning of c/a, which is the ratio of the lattice constants.

Organolead halide perovskite is regarded as the most promising light-harvesting material for next-generation solar cells; however, the intrinsic instability and toxicity of lead are still of great concern. Bismuth is ecofriendly and has electronic properties similar to those of lead, which has gradually attracted interest for optoelectronic applications. However, the valence state of bismuth is different from that of lead, eliminating the possibility of replacing lead by bismuth in organolead halide perovskites. To address this matter, one feasible strategy is to construct B-site double perovskites by the combination of Bi3+ and B+ in 1:1 ratio. In this work, lead-free halide double perovskites of the form Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I) were investigated by first-principles calculations. The electronic properties, optical absorption coefficients, and thermodynamic stability of these compounds were investigated to ascertain their potential application in solar energy conversion. The results provide theoretical support for the exploration of lead-free perovskite materials in potential optoelectronic applications.

To investigate the stability of various Mg-based Laves phases, the formation enthalpy and phonon dispersion were obtained by first-principles calculation. The calculated formation enthalpy and phonon dispersion indicate that MgX2 (X = Al, Co, Ni, Cu, Zn) and Mg2X (X = Ca, Sr, Y, Ba, La) are stable both statically and dynamically. These results are consistent with the experimental results except for MgAl2 and Mg2La. These compounds are considered to be in a metastable state in each binary system. We also used the cluster expansion method to examine the possibility of adding a third element to MgZn2. Our theoretical investigations suggest attractive interaction between Zn and a third element such as Ag, Ca, and Zr in the MgZn2 lattice. However, Ca and Zr replace a small amount of Zn in MgZn2 owing to the instability of MgCa2 and MgZr2, in agreement with the experimental result. Furthermore, it is suggested that Zr becomes stable at the Mg site in the MgZn2 lattice owing to the stability of ZrZn2.

Lead-based perovskite solar cells have gained ground in recent years, showing efficiency as high as 20%, which is on par with that of silicon solar cells. However, the toxicity of lead makes it a nonideal candidate for use in solar cells. Alternatively, tin-based perovskites have been proposed because of their nontoxic nature and abundance. Unfortunately, these solar cells suffer from low efficiency and stability. Here, we propose a new type of perovskite material based on mixed tin and germanium. The material showed a band gap around 1.4–1.5 eV as measured from photoacoustic spectroscopy, which is ideal from the perspective of solar cells. In a solar cell device with inverted planar structure, pure tin perovskite solar cell showed a moderate efficiency of 3.31%. With 5% doping of germanium into the perovskite, the efficiency improved up to 4.48% (6.90% after 72 h) when measured in air without encapsulation.

Cu-Zr based alloys have been used as metallic glass alloys owing to their high glass forming ability (GFA). Ni is added into these alloys to enhance their mechanical property and improve GFA. These Cu-Ni-Zr ternary alloys have a high potential to be used as metallic glass alloys. Herein, we investigated and assessed thermodynamically the phase equilibria of the Cu-Ni-Zr ternary system at 800 °C using the calculation of phase diagram (CALPHAD) method based on the experimental data. Thirty-three alloys were prepared using the arc melting method. At 800 °C, the isothermal section of the Cu-Ni-Zr ternary system composed of 15 single-phase regions, 20 two-phase regions, and 8 three-phase regions; no ternary intermetallic compounds were found. In addition, a continuous solid solution was formed by the Cu10Zr7 and Ni10 Zr7 phases at 800 °C. Furthermore, the thermodynamic parameters were optimized using the phase equilibrium data. The calculated isothermal section and metallic glass region prediction of the Cu-Ni-Zr ternary system were reasonable and satisfactory compared with the literature data.

A powder mixture of Al-Ti-Mg with an equal atomic fraction was subjected to severe plastic deformation using high-pressure torsion (HPT) under 6 GPa at room temperature for full consolidation. Microstructural evolution with respect to straining and annealing was examined by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy. The XRD analysis revealed that Ti prevails in the consolidated sample and a phase transformation occurs from α phase to ω phase during HPT processing while the total fraction of the ω phase increases with straining. Grain refinement to ~100 nm was achieved through the HPT processing for 100 revolutions as well as the formation of nanograined intermetallics such as Al3Ti, AlTi3 and TiAl. The hardness gradually increases with straining, and further increases by annealing at 573 K for 1.5 h due to the formation of an Al12Mg17 phase despite the fact that the harder ω phase was reversely-transformed to the softer α phase and grains were coarsened to ~450 nm. First-principles calculations show that Al and Mg elements are dissolved into the ω − Ti during HPT processing.

To aid the development of Pb-free perovskite solar cells, the stability of the iodide perovskite structure ABI3 has been investigated by first-principles calculations, Bader charge analysis, and the cluster expansion method. At the A sites, methylammonium (MA, CH3NH3+), formamidinium (FA, CH(NH2)2+), and Cs+ were modeled, while at the B sites, one or two elements from Pb, Sn, Ge, In, Ga, Bi, and Sr were examined. For the partially substituted system A(B,B′)I3, we found that the stability strongly depends on the identity of the A-site cation. For example, Cs(B,B′)I3 structures are stabilized by a mixture of divalent cations, such as Pb, Sn, and Ge, at the B site. Concerning the stabilization mechanisms, Coulomb energy gain seems to be the origin of the structural stability in A = Cs structures. From our results, Cs(B,B′)I3, where the B site is occupied by divalent cations, are possible candidates for high stability, lead-free solar cell materials.

A thermodynamic analysis of the Fe-Ti-S ternary system was performed by incorporating first-principles calculations into the calculation of phase diagrams (CALPHAD) method. To evaluate the Gibbs energy, the Debye-Gruneisen model was applied for some sulfides of the Ti-S binary system. In addition, the cluster expansion and cluster variation methods were used for the solid solution phases in the Ti-S binary and (Fe,Ti)S phases. The calculated Ti-S binary phase diagram showed good agreement with the experimental results. The very low solubility of the Ti solid solution in the Ti-S system, as reported by Murray, agreed well with our calculated results. A binodal phase decomposition of the liquid phase was expected in the S-rich region. The Gibbs energy curve of (Fe,Ti)S between FeS and TiS was found to be convex downward. This is characteristic of an isomorphic solid solution, attributed to the attractive interaction between Fe and Ti in (Fe,Ti)S. The vertical phase diagram between FeS and TiS, obtained using the thermodynamic database, was in good agreement with the experimental results of Mitsui et al. The solubility products of (Fe,Ti)S have been experimentally estimated previously. The calculated solubility product agreed with the experimental value of TiS.

Lead-free tin perovskite solar cells (PSCs) show the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly less than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn2+ to oxidize into Sn4+ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of the tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs results in efficiencies higher than 10%, which is the highest reported efficiency to date for pure tin halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction originates from the nonstoichiometric Sn:I ratio rather than the Sn4+:Sn2+ ratio. The amine group in edamine bonded the undercoordinated tin, passivating the dangling bonds and defects, resulting in suppressed charge carrier recombination.

Multi-cations lead perovskite solar cells have shown higher performance than single-cation perovskite solar cells. This compositional engineering of perovskite material retains the optimum tolerance factor while allowing the tuning of the band gap in addition to the enhanced stability of cubic phase perovskite. However, no in-depth explanation has been provided on the relationship between crystal structure of the perovskite and the solar cell efficiency. In this report, we investigate the effect of lattice disordering of FA x MA1−x PbI3 perovskite on the tolerance factor and solar cell efficiency. The lattice disordering estimated using Williamson–Hall plot of XRD analysis revealed that the disordering is lowest when x = 0.2 and highest when x = 1.0. Correspondingly, x = 0.2 showed the highest solar cell performance and long carrier lifetime Our results show that the disordering in α phase of FA x MA1−x PbI3 layer causes lattice deformation which affects the carrier lifetime and solar cell efficiency, instead of the defects on constituent elements.

Effect of impurity elements on the structural stability and electronic state in the tin iodide perovskite, which is useful for tuning carrier concentration to improve the thermoelectric performance, have been investigated using first-principles calculations. MASnI3 (MA ​= ​CH3NH3+) and CsSnI3 are considered as mother materials, and an impurity injection from three types of oxides—Al2O3, TiO2, and Y2O3— acting as scaffolds are considered. Three cations, Al3+, Ti3+, and Y3+, occupy the A or B sites, and one anion O2− occupies an I site. From the estimated formation energy Eform, Al and Ti impurities cause structural instability. In contrast, a Y impurity placed at a B site decrease Eform to −0.05 ​eV/atom and renders the perovskite structure more stable, while a Y impurity at an A site causes instability in the structure. For the calculated structural stability, the bonding analysis clearly explains the difference between the aforementioned sites. The Y–I covalent bonding around E ​= ​−4 ​eV is relatively strong when a Y is placed at a B site. Covalent bonding formed by the impurity elements has a finite contribution to the structural stability, even in the ionic crystal like an iodide perovskite.

The Cu-Zr-Ti alloys are one of popular metallic glass systems due to their high glass-forming ability (GFA), lower cost, and good mechanical properties. The phase equilibria of the Cu-Zr-Ti ternary system are experimentally investigated first to reassess thermodynamic parameters. The isothermal section of the Cu-Zr-Ti ternary system at 703 °C is composed of 15 single phases including the ternary phase-Cu2TiZr, 17 two-phase regions, and 17 three-phase regions. The CuTi2 CuZr2 phases are formed as a continuous solid solution. The CuZr phase was not present in this ternary system. The calculation of phase diagram (CALPHAD) method can be used to predict the metallic-glass region. The suppressed intermetallic compounds, liquid miscibility gap, and spinodal curve were first combined to predict metallic-glass regions. The predicted region is in good agreement with the literature data and experimental results of the bulk-metallic-glass alloys applied in this study.

The bismuth based perovskite with the structure (CH3NH3)3Bi2I9 (MBI) is rapidly emerging as eco-friendly and stable semiconducting material as a substitute for the lead halide perovskites. A relatively higher bandgap of MBI (about 2.1 eV) has been found to be a bottleneck in realizing the high photovoltaic performance similar to that of lead halide based perovskites. We demonstrate the bandgap engineering of novel bismuth based perovskites obtained by in situ sulfur doping of MBI via the thermal decomposition of Bi(xt)3 (xt = ethyl xanthate) precursor. Colors of the obtained films clearly changed from orange to black when annealed from 80 to 120 °C. Formation of sulfur doped MA3Bi2I9 was confirmed by XRD and the presence of sulfur was confirmed through XPS. In this work, obtained sulfur doped bismuth perovskites exhibited a bandgap of 1.45 eV which is even lower than that of most commonly used lead halide perovskites. Hall-Effect measurements showed that the carrier concentration and mobility are much hig...

SnO2 behaves like an n-type semiconductor with a wide energy gap (~ 3.8 eV) and has a tetragonal structure which is similar to the rutile structure. Of the various potential dopants for SnO2, fluorine is preferred because F-doped SnO2 (FTO) films show high transparency and good conductivity. The spray pyrolysis method is the most convenient method because of its simple and inexpensive experimental arrangement and the ease with which doping materials can be added. However, there are few reports on the growth and detailed analysis of FTO films deposited by spray pyrolysis. In previous work1, transparent conducting oxide films of non-doped SnO2 and FTO were deposited on glass substrates at 500 °C by spray pyrolysis in order to determine the effect of spray solution concentration and substrate temperature. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol%. These conditions resulted in a film with an average optical transmittance of 82%, a resistivity of 4.0 × 10-4 Ωcm, a carrier concentration of 4.7 × 1020 cm-3 and a mobility of 34 cm2 (V s)-1. In this work, oriented SnO2 and FTO films were deposited on glass substrates by spray pyrolysis. The (110) or (200) orientation film could be obtained by means of the Sn solution concentration. Furthermore, low surface roughness could be also obtained by means of the sample thickness. Oriented FTO film with low surface roughness could be obtained by controlling two methods such as the Sn solution concentration and thickness. 1 M. Oshima, M and K. Yoshino, J. Electron. Mater. 2010, 39, 819-822.

For thermoelectric materials, the figure of merit depends on the nanostructure, morphology, element doping, and the structure of the interface with other materials. Control of this interface is important in relation to a wide range of thermoelectric material designs such as in organic–inorganic hybrid compounds. Therefore, we evaluated the ease of forming various Bi2Te3 (0 0 1) termination surfaces using formation energy and calculation of phonon dispersion after structure optimization; TeI-1 and TeII terminations exhibited static and dynamic stabilities within various termination structures. In density-of-state and charge-distribution calculations, the TeII termination form exhibited distinctive electronic states around the Fermi energy that originated from the exposed Te atoms; therefore, it is suggested that efficient carrier transfer shall occur at the interface between a TeII surface and another material.

Despite the similarities of the optoelectronic properties between tin halide and lead halide perovskites, the performance of tin perovskite solar cells (PSCs) is still far below that of lead PSCs with highest reported efficiency to date of around 10%. This is due to the chemical instability of tin halide perovskite crystals and the energy band levels mismatch between the perovskite and charge transport layers. In this work, tin halide PSCs with efficiency of more than 13% has been fabricated by regulating the A site cation to achieve a tolerance factor of nearly 1. The partial substitution of formamidinium cation with ethylammonium cation affords a more stable tin perovskite crystal and at the same time suppresses the trap density by as much as 1 order of magnitude. Furthermore, the more favourable energy levels of the EA-substituted tin perovskites enhanced the charge extraction process into the charge transport layers and thus reducing the charge carrier recombination. This work provides a proof that tin-halide PSCs has the potential to compete with more toxic lead-based PSCs, and hopefully will pave the future direction for fabricating more efficient and stable lead-free PSCs.

The thermoelectric properties of the mixed iodide perovskites Cs(B,B′)I3 (B, B′ = Ge, Sn, and Pb), which are related to the well-known organic–inorganic hybrid perovskite used in solar cells, were studied using first-principles calculation. We evaluated the thermoelectric properties of stable partially substituted structures, which were explored by applying a cluster expansion method in our previous work based on the Boltzmann transport equation. The calculated figure of merit, ZT, is larger for N-type systems than for P-type systems. The gradient of the density of states (DOS) at the conduction band edge is steep for all the compositions. This steep conduction edge results in large Seebeck coefficients in N-type systems. Excellent thermoelectric performance can be expected in N-type systems. Among the lead-free compounds, a Cs(Ge,Sn)I3 solid solution with a high germanium content is a possible candidate for a high-ZT material. It was observed that ZT and the Seebeck coefficient increase with increasing gradient of the DOS near the Fermi energy. In addition, ZT and the Seebeck coefficient increase as the band gap increases, which is remarkable in a P-type system. This result indicates a close relationship among the ZT, Seebeck coefficient, and band gap in P-type systems.

Pb-free perovskite solar cells are investigated to eliminate the toxic Pb. However, the Pb-free perovskite solar cell with power conversion efficiency (PCE) of below 9% has been reported mainly because of low open circuit voltage (VOC). In this contribution, the theoretical analysis of the Pb-free perovskite solar cells with an inverted p-i-n planar structure, where the perovskite is FA0.75MA0.25Sn0.95Ge0.05I3 (Sn–Ge perovskite), was therefore conducted using device simulation. It is disclosed that VOC is positively affected by built-in potential across the perovskite absorber (Vbi). The Vbi is primarily governed by conduction band minimum (EC) of electron transporting layer (ETL) and/or work function of back contact (Φ_BC), where they should not be deeper (lower) than the EC (−3.67 eV) of the Sn–Ge perovskite absorber to avoid the Vbi loss for high VOC. Consequently, the ETL and BC materials in the Sn–Ge perovskite solar cells should be appropriately chosen for both suitable conduction band offset of perovskite and ETL, as well as the difference of the EC of perovskite and Φ_BC, thus developing the device structure and increasing Vbi and VOC for the improved PCE.

Solution processed Cesium Tin halide perovskites (CsSnI3) are inorganic crystal to be explored for thermoelectric applications. Here, we report a novel strategy using an inorganic Y2O3 scaffold to improve the thermoelectric performance. The additional Y2O3 influence the CsSnI3 crystal growth and favor more conducting behavior with intrinsic defects (Sn4+) formation. Therefore, the resulting solution processed composite film Y2O3/CsSnI3 show much improved electrical conductivity of ~310 S/cm as compared to ~98 S/cm of pristine CsSnI3 film. Under the influence of Y2O3, the resulting phonon scattering path was enhanced significantly due to formed defects/vacancy and reduced CsSnI3 crystal size, which showed a reduction in thermal conductivity from 0.74 W/mK to 0.28 W/mK. This work paves a new paradigm to improve the thermoelectric performance of solution based thermoelectric generator.

Iron and steels are extensively used as structural materials, and have three primary phase structures: Body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal closed-packed (hcp). Controlling phase stabilities, especially by the use of interstitials, is a universal method that provides a diverse variety of functional and mechanical properties in steels. In this context, hydrogen, which can act as an interstitial species in steels, has been recognized to promote phase transformation from fcc to hcp. However, we here report a dramatic effect of interstitial hydrogen that suppresses this hcp phase transformation. More specifically, the fraction of hcp phase that forms during cooling decreases with increasing diffusible hydrogen content. This new finding opens new venues for thermodynamics-based microstructure design and for development of robust, strong, and ductile steels in hydrogen-related infrastructures.