Single-Layer Zirconium Dihalides ZrX₂ (X = Cl, Br, and I) with Abnormal Ferroelastic Behavior and Strong Anisotropic Light Absorption Ability

Abstract

Recently, two-dimensional (2D) metal halides have brought out an intensive interest for their unique mechanical, electronic, magnetic, and topological properties. Here, we theoretically report the existence of the single-layer (SL) zirconium dihalide materials ZrX2 (X = Cl, Br, and I) using first-principles calculations. SL ZrX2, which can be obtained from its bulk phase through simple mechanical exfoliation, shows the dynamic, thermodynamic, and mechanical stability. Halogen atoms can effectively tune the electronic structure, dipole moment transition, band alignment, and light absorption. Specifically, ZrX2 monolayers intrinsically exhibit a ferroelasticity with an abnormal 120° orientation rotation, possessing a moderate switching barrier of 24–39 meV/atom. Importantly, we observe superior anisotropic light absorption responses on SL ZrX2 in the visible region. Besides, a series of ZrX2-based excitonic solar cells have been proposed, which hold a large power conversion efficiency limit of 12.4–18.7%.

Two-Dimensional Semiconducting ZrNX (X= Cl, Br, I) with a Janus Structure for Solar Energy Utilization

“…To assess the feasibility of the experimental process, the possibility of producing single layers of ZrNX using a mechanical exfoliation strategy is evaluated. The cleavage energy E cl is the minimum energy needed for overcoming the interlayer van der Waals interaction to obtain a monolayer from the bulk, , which is defined as E cl = E 2 − E 1 S , where E 1 and E 2 are the energy of system before and after exfoliation and S is the cleavage area of ZrNX monolayers. A monolayer exfoliating from the five-slab model is used to mimic the process of mechanical exfoliation, and the cleavage energy E cl is calculated.…”

“…Nowadays, efforts are being made to find semiconductor materials that can efficiently use the solar spectrum. Optoelectronic technology based on semiconductors has proven that solar energy can be well utilized, such as solar cells and visible-driven water-splitting photocatalysts. − Traditional three-dimensional (3D) bulk optoelectronic semiconductor materials usually have a high carrier recombination rate, which is not favorable for the effective separation of electron–hole pairs and reduces the efficiency of optoelectronic devices …”

Computational mining of GeH-based Janus III–VI van der Waals heterostructures for solar cell applications

“…By referring to some very recently published works, 41–44 the power conversion efficiency (PCE) η in the limit of 100% external quantum efficiency (EQE) was calculated by the following equation: 45 where 0.65 is the band-fill factor, P ( ħω ) is the solar energy flux at the photon energy value of ħω in air mass 1.5 global (AM 1.5 G) diffuse radiation, the solar energy flux at the value of photon energy ħω , E donor g is the band gap of the donor, and Δ E c is the conduction band offset between the donor and acceptor fixed in vdW heterostructure lattice. The ( E donor g − Δ E c − 0.3) term estimates the maximum open circuit voltage.…”

“…For a vdW heterostructure solar cell, the two component layers can be seen as donor and acceptor. By referring to some very recently published works, [41][42][43][44] the power conversion efficiency (PCE) Z in the limit of 100% external quantum efficiency (EQE) was calculated by the following equation: 45 Based on the deformation potential theory, the carrier mobility was expressed by the following formulation: [46][47][48]…”

Study on strain effects on the electronic and optical properties of hexagonal boron phosphide monolayer

“…2 Over the past decade, more and more 2D graphene-like materials have drawn immense attentions for their adjustable electronic structure and excellent optical properties. [3][4][5][6] 2D III-V compounds have also attracted interest theoretically and experimentally since they have the same isoelectronic properties as group IV semiconductors. 7,8 Dozens of III-V compounds with honeycomb structure have been predicted.…”