DFT investigation of the electronic and optical properties of hexagonal MX2/ZrXO (M = W, Mo and X = S, Se) van der Waals heterostructures for photovoltaic solar cell application.

The van der Waals heterostructure of Janus materials with a TMD monolayer was used to create a two-dimensional class of nanomaterials for photovoltaic solar cell applications. It is one of the potential methods for enhancing the performance of photovoltaic systems. Two monolayers of different 2D materials, Janus (ZrXO) and TMDs (MX2), are stacked together to form the heterojunction. Based on density functional theory structural, electrical, and optical properties were investigated. The favorable stacking and stability of the MX2/ZrXO (M = W, Mo and X = S, Se) van der Waals heterostructures are confirmed through binding energies, phonon dispersion and ab initio molecular dynamics calculations. Standard excitonic peaks, which correspond to the bound valence-band hole and conduction-band electron, as well as excitonic peaks involving the mid-gap charges, can be seen in the system's computed absorption spectrum. MX2/ZrXO van der Waals heterostructures are excellent photovoltaic candidates with a maximum achived power conversion efficiency of above 22%. Furthermore, we discovered that the heterostructure materials have a high absorption efficiency which is good for the intended photovoltaic solar cell application.

First-principles investigation of potential water-splitting photocatalysts and photovoltaic materials based on Janus transition-metal dichalcogenide/WSe2 heterostructures.

Two-dimensional materials have been shown to exhibit exotic properties that make them very interesting for both photo-catalytic and photo-voltaic applications. In this study, van der Waals corrected density functional theory calculations were carried out on heterostructures of MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2. The heterostructures are semiconductors with type II band alignments which are advantageous for electron-hole pair separation. The HSE06 level electronic band gap was found to be 1.093 eV, 1.427 eV and 1.603 eV for MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 respectively. We have considered eight high symmetry stacking patterns for each of the heterostructures, and among them the most stable stacking orders were ascertained based on the interlayer binding energies. The binding energies of the most stable MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures were found to be -0.0604 eV, -0.1721 eV, and -0.3296 eV with an equilibrium interlayer space of 5.75 Å, 4.05 Å, and 4.76 Å respectively. The Power Conversion Efficiency (PCE) was found to be 20, 19.98, and 18.24 percent for the MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures, respectively. The results show that they can serve as suitable photovoltaic materials with high efficiency, thus, opening the possibilities of developing solar cells based on 2D Janus/TMD heterostructures. The most stable heterostructures are also tested for photocatalytic water splitting applications and WSeTe/WSe2 shows excellent photocatalytic activity by being active for full water splitting at pH = 7 and pH = 14, the MoSSe/WSe2 heterostructure is good for the oxygen evolution reaction and WSSe/WSe2 is active for the hydrogen evolution reaction.

Effect of temperature on structural, dynamical, and electronic properties of Sc2Te3 from first-principles calculations.

The compounds Sc2Te3 and Sb2Te3 have the same crystal structure. Ge-Sb-Te alloys are also the most common prototype phase change memory (PCM) compounds in the GeTe-Sb2Te3 pseudo-binary combination. Recently, alloying Sc atoms into Sb2Te3 has enabled sub-nanosecond switching in large conventional phase-change random access memory (PCRAM) devices. However, prior study on the electronic structure and dynamic properties of the Sc2Te3 system is very limited. In this work, we investigate the effect of temperature on the structural, dynamic, and electronic properties of the Sc2Te3 compound through ab initio molecular dynamics simulations. We show that the distorted-octahedral clusters are connected by four-fold rings even at higher temperatures. Moreover, our results clearly illustrate a liquid-to-glass transition temperature, which is between approximately 773 K and 950 K. The effect of temperature changes on the electronic properties of the system manifests as a metal-to-semiconductor transition. The band gap obtained using the mBJLDA functional is twice the value obtained using the PBE functional. Our studies provide useful insight into the local structure and dynamic and electronic properties of the Sc2Te3 system at the atomic level. We hope that this work could stimulate more theoretical work on the development of cache-type phase-change memory and broaden its application in the field of PCM.

A novel WS2 nanowire-nanoflake hybrid material synthesized from WO3 nanowires in sulfur vapor.

In this work, WS2 nanowire-nanoflake hybrids are synthesized by the sulfurization of hydrothermally grown WO3 nanowires. The influence of temperature on the formation of products is optimized to grow WS2 nanowires covered with nanoflakes. Current-voltage and resistance-temperature measurements carried out on random networks of the nanostructures show nonlinear characteristics and negative temperature coefficient of resistance indicating that the hybrids are of semiconducting nature. Bottom gated field effect transistor structures based on random networks of the hybrids show only minor modulation of the channel conductance upon applied gate voltage, which indicates poor electrical transport between the nanowires in the random films. On the other hand, the photo response of channel current holds promise for cost-efficient solution process fabrication of photodetector devices working in the visible spectral range.