Structural and compositional properties of 2D CH3NH3PbI3 hybrid halide perovskite: a DFT study

Two-dimensional (2D) hybrid halide perovskites have been scrutinized as candidate materials for solar cells because of their tunable structural and compositional properties. Results based on density functional theory demonstrate its thickness-dependent stability. We have observed that the bandgap decreases from the mono- to quad-layer because of the transformation from 2D towards 3D. Due to the transformation, the carrier mobility is lowered with the corresponding smaller effective mass. On the other hand, the multilayer structures have good optical properties with an absorption coefficient of about 105 cm−1. The calculated absorption spectra lie between 248 nm and 496 nm, leading to optical activity of the 2D multilayer CH3NH3PbI3 systems in the visible and ultraviolet regions. The strength of the optical absorption increases with an increase in thickness. Overall results from this theoretical study suggest that this 2D multilayer CH3NH3PbI3 is a good candidate for photovoltaic and optoelectronic device applications

Bifunctional catalytic activity of 2D boron monochalcogenides BX (X = S, Se, Te)

Photocatalysis and electrocatalysis are two sustainable and renewable technologies that can meet global energy demands in environmentally friendly ways. According to recent research, 2D boron monochalcogenides in the 1 T and 2 H phases are stable, strong, and broad bandgap semiconductors. Our calculations show a strong UV absorption ability and suitable band edge positions for water splitting oxidation and reduction, making it a good choice for an efficient photocatalyst. The development of bifunctional electrocatalysts has piqued the interest of researchers working in the field of electrocatalysts for fuel cells. The electrocatalytic properties of 2D boron monochalcogenides are also investigated for catalyzing both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The calculated overpotentials for OER/ORR mechanism are found to be 0.92/1.09 for BS (1 T), 1.00/0.59 for BS (2 H), 0.96/1.05 for BSe (1 T), 0.92/0.85 for BSe (2 H), and 1.10/0.92 for BTe (1 T), which are close to benchmark catalysts. The ORR overpotential of BS (2H) is 0.59 V, near well-known catalyst Pt (0.45 V). Therefore, our investigations indicate that the family of 2D materials, boron monochalcogenides, are promising photocatalyst and electrocatalyst candidates for OER and ORR

Two-dimensional boron monochalcogenide monolayer for thermoelectric material

Monochalcogenide materials have outstanding potential for thermoelectric applications. In this paper, we have investigated the electronic structure, vibrational and transport properties of boron chalcogenide BX (X = S, Se, Te) materials. Electronic structure calculations show that each material has an indirect bandgap in the range of 2.92 eV to 1.53 eV. The presence of positive phonon frequencies shows the dynamic stability of the materials. We also calculated the mobility (m) and relaxation time (t) of all the materials. Additionally, as the 2D boron monochalcogenide BX (X = S, Se, Te) materials have superior carrier mobility, they have a small effective mass of electrons. The 1T and 2H phases of the BS monolayer have superior electron carrier mobilities of 11 903.07 and 11 651.61 cm(2) V-1 s(-1). We also found that for the low and mid-temperature range (200-450 K), all the materials have a high electronic figure of merit ZT(e) nearly equal to 1, with the exception of the BS 2H phase. The BSe 1T phase has high ZT(e) = 1.022, which is the maximum across all the materials. These theoretical investigations suggest that boron monochalcogenide BX (X = S, Se, Te) materials have promise for applications in high-performance thermoelectrics

Metal-functionalized 2D boron sulfide monolayer material enhancing hydrogen storage capacities

In the present work, we have systematically investigated the structural, electronic, vibrational, and H2 storage properties of a layered 2H boron sulfide (2H-BS) monolayer using spin-polarized density functional theory (DFT). The pristine BS monolayer shows semiconducting behavior with an indirect bandgap of 2.83 eV. Spin-polarized DFT with van der Waals correction suggests that the pristine BS monolayer has weak binding strength with H2 molecules, but the binding energy can be significantly improved by alkali metal functionalization. A system energy study indicates the strong bonding of alkali metals with the BS monolayer. The Bader charge analysis also concludes that a considerable charge is transferred from the metal to the BS monolayer surface, which was further confirmed by the iso-surface charge density profile. All functionalized alkali metals form cations that can bond multiple H2 molecules with sufficient binding energies, which are excellent for H2 storage applications. An ideal range of adsorption energy and practicable desorption temperature promises the ability of the alkali metal functionalized BS monolayer as an efficient material for hydrogen storage

Enhancement of hydrogen storage capacity on co-functionalized GaS monolayer under external electric field

Hydrogen storage properties of co-functionalized 2D GaS monolayer have been systematically investigated by first-principles calculations. The strength of the binding energy of hydrogen (H-2) molecules to the pristine GaS surface shows the physisorption interactions. Co-functionalized GaS sheet by Li, Na, K and Ca atoms enhanced the capacity of binding energies of hydrogen and strength of hydrogen storage considerably. Besides, DFT calculations show that there is no structural deformation during H-2 desorption from cofunctionalized GaS surface. The binding energies of per H-2 molecules is found to be 0.077 eV for pristine GaS surface and 0.064 eV-0.37 eV with the co-functionalization of GaS surface. Additionally, in the presence of applied external electric field enhanced the strength of binding energies and it is found to be 0.09 eV/H-2 for pristine GaS case and 0.19 eV/H-2 to 0.38 eV/H-2 for co-functionalized GaS surface. Among the studied GaS monolayer is found to be the superior candidate for hydrogen storage purposes. The theoretical studies suggest that the electronic properties of the 2D GaS monolayer show the electrostatic behavior of hydrogen molecules which confirms by the interactions between adatoms and hydrogen molecules before and after hydrogen adsorption. (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC

Size and edge roughness effects on thermal conductivity of pristine antimonene allotropes

© 2015 Elsevier B.V. All rights reserved. Novel two-dimensional antimonene, is recently reported to be stable by first principles calculations Wang et al. [35]. Its thermal properties are now investigated using the phonon Boltzmann transport method. Specifically, the size and edge roughness effects on the thermal conductivity of antimonene allotropes, namely α-Sb and β-Sb are determined. The semiconducting α-Sb and β-Sb have the rectangular and hexagonal unit cells, respectively. We find that thermal conductivity increases with size, and decreases with the edge roughness of the antimonene allotropes. Higher thermal conductivity occurs for α-Sb, and its distinct characteristics in the in-plane acoustic branches are found to be associated with the anisotropic nature of the 2D lattice

Bulk and monolayer As2S3 as promising thermoelectric material with high conversion performance

The electronic and thermoelectric properties of recently synthesized As2S3 in the form of 2D by experiment have been investigated in this work. The thermoelectric properties of As2S3 has been studied by the first-principles calculations and the Boltzmann Transport theory. The result shows that As2S3 has indirect band gap of 2.31 eV for monolayer and 2.08 eV for bulk. From phonon dispersion spectra, both bulk and monolayer have dynamical stability. The Seebeck coefficient (S) as a function of temperature is investigated for monolayer and bulk of As2S3 and its values at 300 K temperature are 188 and 298 mu V/K. Also, the values of S are drastically decreasing when temperature increases in bulk As2S3 while in case of monolayer As2S3, the values of S have less variation with increasing temperature. The electronic figure of merit (ZT(e)) for bulk As2S3 is found to be 5.04 at 300 K while at higher temperature ZT(e) values significantly reduced to 3.76. For monolayer As2S3, the electronic figure of merit, ZT(e) is also showed higher value of 1.84 at 300 K and at higher temperature it has similar to 2.75. These investigation shows that the bulk and monolayer have new materials for the potential applications in the thermoelectric devices

Achieving ultrahigh carrier mobilities and opening the band gap in two-dimensional Si2BN

Recently, a two-dimensional (2D) SiBN monolayer material made of silicon, boron and nitrogen, was theoretically predicated and has attracted interest in the scientific community. Due to its 2D planar nature with high formation energy, SiBN monolayers can be flexible and strong like graphene and also exhibit captivating properties like those of other 2D materials. Motivated by this fascinating graphene-like monolayer of SiBN, we have investigated its structural and electronic properties based on first-principles calculations. The electronic band structure of pure SiBN shows metallic behaviour. We have discovered that the band gap of SiBN monolayer can be tuned to 102 meV by applying external electric fields and mechanical strain. The band gap opening occurs at 5% strain, where the bond angles between the nearest neighbours become nearly equal. The band gap opening occurs at a small external electric field of 0.4 V Å. More interestingly, at room temperature, the electron mobility of SiBN is 4.73 × 10 cm V s, which is much larger than that of graphene, while the hole mobility is 1.11 × 10 cm V s, slightly smaller than the electron mobility. The ultrahigh carrier mobility of SiBN may lead to many novel applications in high-performance electronic and optoelectronic devices. These theoretical results suggest that the SiBN monolayer exhibits multiple effects that may significantly enhance the performance of SiBN based electronic devices