Floquet band engineering and topological phase transitions in 1T’ transition metal dichalcogenides

Using ab initio tight-binding approaches, we investigate Floquet band engineering of the 1T’ phase of transition metal dichalcogenides (MX2, M = W, Mo and X = Te, Se, S) monolayers under the irradiation with circularly polarized light. Our first principles calculations demonstrate that light can induce important transitions in the topological phases of this emerging materials family. For example, upon irradiation, Te-based MX2 undergoes a phase transition from quantum spin Hall (QSH) semimetal to time-reversal symmetry broken QSH insulator with a nontrivial band gap of up to 92.5 meV. On the other hand, Se- and S-based MX2 undergoes the topological phase transition from the QSH effect to the quantum anomalous Hall (QAH) effect and into trivial phases with increasing light intensity. From a general perspective, our work brings further insight into non-equilibrium topological systems.

Conduction Band Engineering of Half-Heusler Thermoelectrics Using Orbital Chemistry

Semiconducting half-Heusler (HH, XYZ) phases are promising thermoelectric materials owing to their versatile electronic properties. Because the valence band of half-Heusler phases benefits from the valence band extrema at several...

Twist-angle two-dimensional superlattices and their application in (opto)electronics

Twist-angle two-dimensional systems, such as twisted bilayer graphene, twisted bilayer transition metal dichalcogenides, twisted bilayer phosphorene and their multilayer van der Waals heterostructures, exhibit novel and tunable properties due to the formation of Moiré superlattice and modulated Moiré bands. The review presents a brief venation on the development of “twistronics” and subsequent applications based on band engineering by twisting. Theoretical predictions followed by experimental realization of magic-angle bilayer graphene ignited the flame of investigation on the new freedom degree, twist-angle, to adjust (opto)electrical behaviors. Then, the merging of Dirac cones and the presence of flat bands gave rise to enhanced light-matter interaction and gate-dependent electrical phases, respectively, leading to applications in photodetectors and superconductor electronic devices. At the same time, the increasing amount of theoretical simulation on extended twisted 2D materials like TMDs and BPs called for further experimental verification. Finally, recently discovered properties in twisted bilayer h-BN evidenced h-BN could be an ideal candidate for dielectric and ferroelectric devices. Hence, both the predictions and confirmed properties imply twist-angle two-dimensional superlattice is a group of promising candidates for next-generation (opto)electronics.

>35% 5-junction space solar cells based on the direct bonding technique

Multijunction solar cells are the highest efficiency photovoltaic devices yet demonstrated for both space and terrestrial applications. In recent years five-junction cells based on the direct semiconductor bonding technique (SBT), demonstrates space efficiencies >35% and presents application potentials. In this paper, the major challenges for fabricating SBT 5J cells and their appropriate strategies involving structure tunning, band engineering and material tailoring are stated, and 4-cm 2 35.4% (AM0, one sun) 5J SBT cells are presented. Further efforts on detailed optical managements are required to improve the current generating and matching in subcells, to achieve efficiencies 36%–37%, or above.