Superhalogens as building blocks of two-dimensional organic-inorganic hybrid perovskites for optoelectronics applications

Quasi-2D lead-free halide perovskite using superalkali cations for red-light-emitting diodes

Two dimensional halide perovskites have attracted intense attention, but there is no study to consider quasi-2D lead-free perovskites with superalkali cations as potential emitting materials. Herein, the quasi-2D [C₆H₅(CH₂)₂NH₃]₂H₅O₂Sn₂Br₇ perovskite is systematically studied by using ab initio molecular dynamics simulation and first principles calculations. The calculated results show that the quasi-2D perovskite has negative formation energy, small effective hole and electron masses, stable dynamics performance, suitable exciton binding energy and direct band gap, and H₅O₂ superalkali cations that don't agglomerated. Moreover, the band-edge states do not change for the quasi-2D perovskite after ab initio molecular dynamics simulation of 3 ps. Overall, our results indicated that the quasi-2D [C₆H₅(CH₂)₂NH₃]₂H₅O₂Sn₂Br₇ perovskite may be applied to red-light-emitting diodes.

DFT study of superhalogen-doped borophene with enhanced nonlinear optical properties

The concern of the present study is to investigate the nonlinear optical properties of superhalogen-doped borophene owing to its broad applications. The first principle study of the material for its nonlinear optical properties elaborated its use for electrical and optical applications. The superhalogen-based borophene in lithium ion-based batteries and medical appliances have made it one of the most potential materials for optoelectronics. First, hyperpolarizability (β_o) of pure and doped B₃₆ is computed, and the difference between their values was examined. The vertical ionization energy (VIE) was calculated for pure and doped systems. The interaction energy (E_i) for all combinations was computed. It would be expected to be one of the best materials to have high capacity and resistance. For all the calculations and to calculate the highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap, the density functional theory (DFT) method was used. It is predicted that these combinations are more beneficial and can display better nonlinear optical (NLO) properties in electronic devices. Superhalogen-doped BF₄ borophene-36 ground state optimized geometry, frontier molecular orbitals HOMO and LUMO, maximum absorption (λ_max), density of states (DOS) analysis, and electrostatic potential diagram (MEP) are displayed here_.

High-Performance Photovoltaic Materials Based on the Superlattice Structures of Organic-Inorganic Halide Perovskite and Superhalogen Hybrid Perovskite

The use of superlattice structures is an attractive strategy for expanding the family of perovskites and obtaining excellent optoelectronic materials. Mixing of cations and partial replacement of halogens by superhalogens are advantageous for improving the stability and optoelectronic properties of hybrid perovskites. Herein, the superlattice structures of the (CsPbI₃)_n/MAPbI₂BF₄, (FAPbI₃)_n/MAPbI₂BF₄, (MAPbI₃)_n/CsPbI₂BF₄, and (FAPbI₃)_n/CsPbI₂BF₄ hybrid perovskites were investigated using first-principles density functional theory calculations. The results show that these superlattice structures have tunable direct band gaps and small effective electron and hole masses. Additionally, the charge densities for the valence band maximum and conduction band minimum states are located in different regions of the superlattices. Suggesting that these structures are type-II superlattices that show greatly reduced electron-hole recombination rates. Excellent optical absorption properties for all of perovskite superlattices and the calculated power conversion efficiency of 22.77% for the single-junction solar cells based on the (FAPbI₃)₃/MAPbI₂BF₄ and (FAPbI₃)₃/CsPbI₂BF₄ perovskites were obtained.

Building Better Batteries in the Solid State: A Review

Most of the current commercialized lithium batteries employ liquid electrolytes, despite their vulnerability to battery fire hazards, because they avoid the formation of dendrites on the anode side, which is commonly encountered in solid-state batteries. In a review two years ago, we focused on the challenges and issues facing lithium metal for solid-state rechargeable batteries, pointed to the progress made in addressing this drawback, and concluded that a situation could be envisioned where solid-state batteries would again win over liquid batteries for different applications in the near future. However, an additional drawback of solid-state batteries is the lower ionic conductivity of the electrolyte. Therefore, extensive research efforts have been invested in the last few years to overcome this problem, the reward of which has been significant progress. It is the purpose of this review to report these recent works and the state of the art on solid electrolytes. In addition to solid electrolytes stricto sensu, there are other electrolytes that are mainly solids, but with some added liquid. In some cases, the amount of liquid added is only on the microliter scale; the addition of liquid is aimed at only improving the contact between a solid-state electrolyte and an electrode, for instance. In some other cases, the amount of liquid is larger, as in the case of gel polymers. It is also an acceptable solution if the amount of liquid is small enough to maintain the safety of the cell; such cases are also considered in this review. Different chemistries are examined, including not only Li-air, Li-O2, and Li-S, but also sodium-ion batteries, which are also subject to intensive research. The challenges toward commercialization are also considered.

Magnesium-Based Oxyfluoride Superatoms: Design, Structure, and Electronic Properties

The ability of mixed ligands to form stable dinuclear and trinuclear magnesium-based superatoms has been investigated theoretically. The Mg₂F_{5-2 m}O _m and Mg₃F_{7-2 m}O _m systems (where m = 1-3) were found able to form stable and strongly bound anionic clusters, and those assumptions were validated by (i) the analysis of the geometrical stability; (ii) the estimated Gibbs free energies for the most probable disproportion paths these clusters might be vulnerable to (which allows examining their thermodynamic stabilities); (iii) the localization of the electron density; and (iv) the adiabatic electron affinity (AEA), vertical electron detachment energy (VDE), and adiabatic electron detachment energy (ADE) values calculated for the studied systems. It is demonstrated that the stability of the anionic daughters of these clusters increases with the number of electronegative ligands, and Mg _nF_{2 n+1-2 m}O _m^- ( n = 2, 3; m = 1-3) clusters are stable against electron emission. The largest electron binding energy was found for the Mg₃F₅O^- anion (VDE = 6.826 eV). The strong VDE dependence on (i) the geometrical structure, (ii) the number of central atoms, (iii) ligand type, and (iv) bonding/antibonding character of the highest molecular orbital (HOMO) was also remarked upon and discussed.

Synergistic Effect between Different Coordination Geometries of Lanthanides and Various Coordination Modes of 2-Picolinic Acid Ligands Tuning Three Types of Rare 3d-4f Heterometallic Tungstoantimonates

Three types of N-heterocyclic aromatic acid decorated 3d-4f heterometallic Keggin-type tungstoantimonates: Na₄[Ln(H₂O)₅]₂[Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]·26H₂O [Ln³⁺ = La³⁺ (1), Pr³⁺ (2), Nd³⁺ (3), Sm³⁺ (4), Eu³⁺ (5)], Na₆H₄[Fe₂W₄O₉(H₂O)₂(Hpic)₄ (B-β-SbW₉O₃₃)₂][Ln(H₂O)₈]₂[Fe₄W₂O₇(H₂O)₄(pic)₂(Hpic)₂(B-β-SbW₉O₃₃)₂]·38H₂O [Ln³⁺ = Gd³⁺ (6), Dy³⁺ (7)], and Na₂H₂{[Ln(H₂O)₆]₂[Fe₄(H₂O)₂(Hpic)₂(pic)₂(B-β-SbW₉O₃₃)₂]}₂·44H₂O [Ln³⁺ = Ho³⁺ (8), Er³⁺ (9), Hpic = 2-picolinic acid] have been prepared. 1-5 comprise a quadripic-inserted Krebs-type [Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]^10- moiety supported by two [Ln(H₂O)₅]³⁺ groups on both sides where it can be considered that four pic ligands replace eight aqua ligands located on the original Krebs-type [Fe₄(H₂O)₁₀(B-β-SbW₉O₃₃)₂]^10- fragment to form the [Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]^10- moiety. Remarkably, the quadripic-inserted subunits are further concatenated through the coordination role of the pic ligands to create a 3-D heterometallic framework. In contrast, the molecular units of 6-7 contain two kinds of non-Krebs-type quadripic-inserted [Fe₂W₄O₉(H₂O)₂(Hpic)₄(B-β-SbW₉O₃₃)₂]^6- and {[Ln(H₂O)₈]₂[Fe₄W₂O₇(H₂O)₄(pic)₂(Hpic)₂(B-β-SbW₉O₃₃)₂]}^4- moieties. The molecular units of 8-9 contain two identical quadripic-inserted Krebs-type {[Ln(H₂O)₆]₂[Fe₄(H₂O)₂(Hpic)₂(pic)₂(B-β-SbW₉O₃₃)₂]}^2- moieties, and both display a 1-D heterometallic double chain. For all we know, 1-9 stand for the first 3d-4f heterometallic tungstoantimonate hybrids functionalized by pic ligands. Particularly, the solid-state NIR photoluminescence (PL) spectrum in the range of 800-1450 nm of 3 and the solid-state visible PL spectra in the range of 500-750 nm of 4, 5, 7, and 8 at room temperature display the featured fluorescence emission bands stemming from Ln³⁺ cations. In the PL emission procedures of 5 and 7, energy transfer from [B-β-SbW₉O₃₃]^9- fragments and pic ligands to Ln³⁺ ions has been observed. Additionally, the correlated color temperatures of 4, 5, 7, and 8 are indexed to 2731, 2020, 4557, and 1685 K, respectively.

Design of superhalogens using a core-shell structure model

Superhalogens, which have larger electron affinity than any halogen, play an important role in physical chemistry and materials design because of their applications in hydrogen storage and lithium-ion batteries. Inspired by the unique geometries and electronic properties of II-VI/III-V cage clusters, particularly the experimentally synthesized B₁₂N₁₂, we propose a core-shell structure model to design new superhalogens. The idea is assessed by conducting ab initio calculations on endohedral cage clusters X@B₁₂N₁₂ (X = F, Cl, Br) and other similar systems. With an exceptionally large electron affinity of 5.36 eV, the stable F@B₁₂N₁₂ cluster behaves as a novel superhalogen that can serve as a building block for Li salts and hyperhalogens. The findings highlight a new route for the discovery of superhalogens and provide useful building blocks for the bottom-up design of materials.

Li-rich antiperovskite superionic conductors based on cluster ions

Enjoying great safety, high power, and high energy densities, all-solid-state batteries play a key role in the next generation energy storage devices. However, their development is limited by the lack of solid electrolyte materials that can reach the practically useful conductivities of 10^-2 S/cm at room temperature (RT). Here, by exploring a set of lithium-rich antiperovskites composed of cluster ions, we report a lithium superionic conductor, Li₃SBF₄, that has an estimated 3D RT conductivity of 10^-2 S/cm, a low activation energy of 0.210 eV, a giant band gap of 8.5 eV, a small formation energy, a high melting point, and desired mechanical properties. A mixed phase of the material, Li₃S(BF₄)_0.5Cl_0.5, with the same simple crystal structure exhibits an RT conductivity as high as 10^-1 S/cm and a low activation energy of 0.176 eV. The high ionic conductivity of the crystals is enabled by the thermal-excited vibrational modes of the cluster ions and the large channel size created by mixing the large cluster ion with the small elementary ion.

Atomic-Level Design of Water-Resistant Hybrid Perovskites for Solar Cells by Using Cluster Ions

Organic-inorganic hybrid perovskites have emerged as the most promising material in the development of next-generation solar cells. However, the stability of these materials exemplified by CH₃NH₃PbI₃ is the most pressing challenge; it readily decomposes when exposed to moisture. Here, we show how one can use a particular type of cluster ions, known as pseudohalides, to enhance the water resistance of the hybrid perovskite, while maintaining its favorable electronic properties. Starting with a simple physical model, we propose a new class of water-resistant hybrid perovskites as solar-cell absorbers based on the cluster ions by using DFT calculations and ab initio molecular dynamics. Limitations of applying the currently known pseudohalides for our purpose are also discussed.

Rational design of super-alkalis and their role in CO2 activation

Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al₃⁺, Mn(B₃N₃H₆)₂⁺, B₉C₃H₁₂⁺, and C₅NH₆⁺ which obey the jellium shell closure rule, the 18-electron rule, the Wade-Mingos rule, and Hückel's aromatic rule, respectively. We further show that the ability of superalkalis to transfer an electron easily can be used to activate a CO₂ molecule by transforming it from a linear to a bent structure. These results, based on density functional theory with generalized gradient approximation for exchange-correlation potential, open the door to a new class of catalysts for CO₂ activation.

Iron-based magnetic superhalogens with pseudohalogens as ligands: An unbiased structure search

We have performed an unbiased structure search for a series of neutral and anionic FeL₄ (L = BO₂, CN, NO₂, NO₃, OH, CH₃, NH₂, BH₄ and Li₂H₃) clusters using the CALYPSO (Crystal structure Analysis by Particle Swarm Optimization) structure search method. To probe the superhalogen properties of neutral and anionic FeL₄ clusters, we used density-functional theory with the B3LYP functional to examine three factors, including distribution of extra electron, pattern of bonding and the nature of the ligands. Theoretical results show that Fe(BO₂)₄, Fe(NO₃)₄ and Fe(NO₂)₄ can be classified as magnetic superhalogen due to that their electron affinities even exceed those of the constituent ligands. The magnetic moment of Fe atom is almost entirly maintained when it is decorated with various ligands except for neutral and anionic (Li₂H₃)₄. Moreover, the current work is also extended to the salt moieties formed by hyperhalogen/superhalogen anion and Na⁺ ion. It is found that these salts against dissociation into Na + FeL₄ are thermodynamic stable except for Na[Fe(OH)₄]. These results provides a wealth of electronic structure information about FeL₄ magnetic superhalogens and offer insights into the synthesis mechanisms.

Synthesis of novel bis(Triol)-functionalized Anderson clusters serving as potential synthons for forming organic–inorganic hybrid chains

Three novel bis(Triol)-functionalized Anderson cluster derivatives (POM–L–POM, POM–L, L–POM–L) were efficiently synthesized, which manifested interesting self-assembly and synergistic effect.

Role of ligands in the stability of BnXn and CBn−1Xn (n = 5–10; X = H, F, CN) and their potential as building blocks of electrolytes in lithium ion batteries

We predict a series of boron-cage-based stable (di-)anions, and demonstrate them to be high-performance electrolytes in Li-ion batteries.