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Halide perovskites have distinguished themselves among the numerous optoelectronic materials due to their versatile processing technology and exceptional optical response. Unfortunately, their stability and toxicity from heavy metals severely hamper their development, in addition to the challenge of further improving photovoltaic performance. Hence, a lead-free perovskite-based heterojunction, C2N/CsGeI3, is investigated using a hybrid density functional, including electron structures, charge density differences, optical properties and more. The study reveals the presence of a built-in electric field directed from the CsGeI3 to the C2N layer. Moreover, based on the work function, it is confirmed that the electrons are transferred in a Z-scheme mechanism after the CsGeI3 contacts with the C2N layer. Under light irradiation, the construction of the C2N/CsGeI3 heterojunction significantly enhances optical absorption within the range of visible-light wavelengths. Additionally, the impact of interfacial strain on the C2N/CsGeI3 is explored and discussed. These findings not only suggest that the C2N/CsGeI3 heterojunction holds promise for photovoltaic applications but also provide a theoretical insight into lead-free perovskite-based functional materials. [ABSTRACT FROM AUTHOR]

Single–atom catalysts (SACs) have attracted wide attention to be acted as potential electrocatalysts for nitrogen reduction reaction (NRR). However, the coordination environment of the single transition metal (TM) atoms is essential to the catalytic activity for NRR. Herein, we proposed four types of 3‐, 4‐coordinated and π–d conjugated TMxB3N3S6 (x=2, 3, TM=Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Tc, Ru, Hf, Ta, W, Re and Os) monolayers for SACs. Based on density functional theory (DFT) calculations, I‐TM2B3N3S6 and III‐TM3B3N3S6 are the reasonable 3‐coordinated and 4‐coordinated structures screening by structure stable optimizations, respectively. Next, the structural configurations, electronic properties and catalytic performances of 30 kinds of the 3‐coordinated I‐TM2B3N3S6 and 4‐coordinated III‐TM3B3N3S6 monolayers with different single transition metal atoms were systematically investigated. The results reveal that B3N3S6 ligand is an ideal support for TM atoms due to existence of strong TM‐S bonds. The 3‐coordinated I‐V2B3N3S6 is the best SAC with the low limiting potential (UL) of −0.01 V, excellent stability (Ef=−0.32 eV, Udiss=0.02 V) and remarkable selectivity characteristics. This work not only provides novel π–d conjugated SACs, but also gives theoretical insights into their catalytic activities and offers reference for experimental synthesis. [ABSTRACT FROM AUTHOR]

We propose a reconfigurable spin tunnel diode based on a small spin-gapped semiconductor (non-doped VS2 monolayer) and semi-metallic magnets (doped VS2 monolayer) separated by a thin insulating tunneling barrier (h-BN). By using first-principles calculations assisted by the nonequilibrium Green's function method, we have carried out a comprehensive study of spin-dependent current and spin transport properties while varying the bias. The device exhibited a magnetization-controlled diode-like behavior with forward-allowed current under antiparallel magnetizations and reverse-forbidden current under parallel magnetizations at the two electrodes. The threshold voltage is tunable by the hole doping density of VS2 monolayers. The doping effect on VS2 monolayers indicates that the magnetic moments, the Heisenberg exchange parameters and Curie temperatures can be monotonically reduced by a larger hole doping density. Our study on VS2 heterostructures has presented a simple and practical device strategy with very promising applications in spintronics. [ABSTRACT FROM AUTHOR]

Lead-halide perovskites have attracted much attention over the past decade, while two main issues, i.e., the lead-induced toxicity and materials' instability, limit their further practice in widespread applications. To overcome these limitations, an effective alternative is to design lead-free perovskite materials with the substitution of two divalent lead ions with a pair of monovalent and trivalent metal ions. However, fundamental physics and chemistry about how tuning material's composition affects the crystal phase, electronic band structures, and optoelectronic properties of the material have yet to be fully understood. In this work, we conducted a series of density functional theory calculations to explore the mechanism that how various monovalent metal ions influence the crystal and electronic structures of lead-free Cs2MBiCl6 perovskites. We found that the Cs2MBiCl6 (M = Ag, Cu, and Na) perovskites preferred a cubic double perovskite phase with low carrier effective masses, while the Cs2MBiCl6 (M = K, Rb, and Cs) perovskites favored a monoclinic phase with relatively high carrier effective masses. The different crystal phase preferences were attributed to the different radii of monovalent metal cations and the orbital hybridization between the metal and Cl ions. The calculation showed that all Cs2MBiCl6 perovskites studied here exhibited indirect bandgaps. Smaller bandgap energies for the perovskites with a cubic phase were calculated than those of the monoclinic phase counterparts. Charge density difference calculation and electron localization functional analysis were also conducted and revealed that the carrier mobility can be improved via changing the characteristics of metal-halide bonds through compositional and, thus, crystal structure tuning. Our study shown here sheds light on the future design and fabrication of various lead-free perovskite materials for optoelectronic applications. [ABSTRACT FROM AUTHOR]

In-depth understandings of charge carrier transfer dynamics in any artificial catalytic system are of critical importance for the future design of highly efficient photocatalysts. Herein, we synthesized sub-monolayer ZnSe partial-shell coated CdSe/CdS core/shell quantum dots in a controlled fashion. The ZnSe decorated quantum dots were employed as a model catalyst for photogeneration of H2 under light illumination. Both theoretical calculations and experimental results unravel that the growth of ZnSe partial-shell would retard the photogenerated electron transfer, and meanwhile, accelerate the corresponding hole migration process during the H2 photogeneration reaction in the artificial photocatalytic system. As such, the performance of the relevant photocatalytic system can be modulated and optimized, and accordingly, a plausible underlying mechanism is rationalized. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials have attracted great attention in solving the problems in the waste heat field, while low figure of merit and poor material stability drastically limit their practical applications. In this work, a two-dimensional (2D) Sc2Si2Te6 monolayer was systematically explored as a promising TE material via ab initio methods. The results reveal that the Sc2Si2Te6 monolayer possesses an indirect band gap with a rhombohedral crystal phase and exhibits excellent dynamic stability. The lower electronic/lattice thermal conductivity and higher electron carrier mobility result in good n-type power factor parameters between 6.24 × 1010 and 1.5 × 1011 W m−1 s−1 K−2 from 300 to 700 K. Such combined merits of low thermal conductivity and high power factor parameters endow the Sc2Si2Te6 monolayer with superior thermoelectric properties with figure of merit (ZT) values of 1.41 and 3.81 at 300 K and 700 K, respectively. This study presented here can shed light on the future design of various 2D materials for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Septuple-atomic-layer MoSi2N4 has emerged as a promising and non-precious energy conversion material due to its stable and unique crystal structures. Unfortunately, the MoSi2N4 monolayer shows an inert catalytic active feature due to the large positive Gibbs free energy (ΔGH). To overcome the main drawback, an effective alternative is to design MoSi2N4 with different modifications. The results show that the electronic properties can be significantly tailored with the atomic vacancies, substitutions and biaxial strains with the band gap reduced to near zero eV when B and O dopants are incorporated into MoSi2N4 monolayer. Moreover, the continuous decrease of band gap can also be obtained by applying the tensile strains on MoSi2N4 monolayer. The ELF and charge transfer analyses show that the modifications induce various cation–anion bond features for the MoSi2N4. The changes of bond features greatly enhance the hydrogen adsorption on the MoSi2N4, rendering a suitable ΔGH (near 0 eV) for HER. The obvious enhancement is owing to the H-1 s orbital splitting into two parts located below and above Fermi energy due to the strong hybridization between the hydrogen atom and catalyst. These results suggest the great potential of such modified MoSi2N4 monolayer as highly efficient HER electrocatalyst for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, density-functional theory calculations are performed to explore how the biaxial strain and electric field affect the electronic properties of MoS2/ScCl3 van der Waals (vdW) heterostructure. The pristine MoS2/ScCl3 vdW heterostructure is a semiconductor with an indirect bandgap of 1.55 eV which is also with type II band alignment. The results show that the bandgap, band alignment, and effective mass of the MoS2/ScCl3 heterostructure can be effectively modulated by mechanical strain and external electric field. The bandgap decreases for both tensile and compressive strains and a transition from type II band alignment to type I upon tensile strain. When positive field applying (from MoS2 to the ScCl3), the type II heterostructure transforms to type I and the bandgap remains about 1.55 eV. The type II heterostructure can remain but the bandgap is reduced as the negative electric field is applied. These results suggest that MoS2/ScCl3 heterostructure is a possible candidate for high-performance nanoelectronic devices. [ABSTRACT FROM AUTHOR]

A low thermal conductivity and a high power factor are essential for efficient thermoelectric materials. The lattice thermal conductivity can be reduced by reducing the dimensions of the materials, thus improving the thermoelectric performance. In this work, the electronic, carrier and phonon transport and the thermoelectric properties of ZrNX (X = Cl, Br, and I) monolayers were investigated using density functional theory and Boltzmann transport theory. The electronic and phonon transport show anisotropic properties. The thermal conductivities are 20.8, 14.6 and 12.4 W m−1 K−1 at room temperature along the y-direction for the ZrNCl, ZrNBr, and ZrNI monolayers, respectively. Combining the low lattice thermal conductivity and the high power factor results in an excellent thermoelectric performance of the ZrNX monolayers. The thermoelectric figure of merit of ZrNX monolayers can reach magnitudes of ∼0.49–3.15 by optimal hole and electron concentrations between 300 and 700 K. ZrNX monolayers with high ZT values for n- and p-type materials would thus be novel, promising candidate 2D thermoelectric materials for heat–electricity conversion. [ABSTRACT FROM AUTHOR]

The threshold displacement energies (TDEs) of lattice atoms in lithium ferrite (LiFe5O8) are calculated using first‐principles molecular dynamics simulations. The TDEs vary with crystal direction and sublattice. The weighted average TDEs are 34.65, 28.54, 38.85, 37.92, and 34.31 eV for FeTetra, FeOct, Li, OI, and OII atoms in LiFe5O8, respectively. The FeOct primary knock‐on atom (PKA) has the smallest TDE. Various defects, including vacancies (VFeTetra, VFeOct, VLi, VOI, and VOII), interstitials (IFe, ILi and IO), antisite defects (LiFeOct, LiFeTetra and FeLi), split interstitials (DFeFe, DLiLi, DLiFe, and DOO), crowding defects (CrowFeFeFe) and exchange defects (OO), are formed by low‐energy recoil events. The effect of the presence of these defects on the magnetic behavior in LFO is investigated using density functional theory. The occupation of the octahedral and tetrahedral sublattice in LiFe5O8 has an important effect on magnetization. The net magnetization decreases or increases when a Fe atom at an octahedral or tetrahedral site is replaced by a nonmagnetic atom, respectively. These results are helpful for using irradiation to tune the magnetic behavior of LiFe5O8 and applying magnetic devices based on LiFe5O8 in the presence of irradiation. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots (QDs) have attracted tremendous attention in the field of photocatalysis, owing to their superior optoelectronic properties for photocatalytic reactions, including high absorption coefficients and long photogenerated carrier lifetimes. Herein, by choosing 2‐(3,4‐dimethoxyphenyl)‐3‐oxobutanenitrile as a model substrate, we demonstrate that the stereoselective (>99 %) C−C oxidative coupling reaction can be realized with a high product yield (99 %) using zwitterionic ligand capped CsPbBr3 perovskite QDs under visible light illumination. The reaction can be generalized to different starting materials with various substituents on the phenyl ring and varied functional moieties, producing stereoselective dl‐isomers. A radical mediated reaction pathway has been proposed. Our study provides a new way of stereoselective C−C oxidative coupling via a photocatalytic means using specially designed perovskite QDs. [ABSTRACT FROM AUTHOR]