Phase-Dependent Excitonic Light Harvesting and Photovoltaic Limits in Monolayer Y2TeO2 MOenes

Abstract

We investigate phase-dependent electronic and excitonic phenomena in monolayer Y2TeO2 MOenes in the 1T and 2H polymorphs using first-principles theory and an effective many-body framework. Phonon spectra and elastic stability criteria establish both phases as dynamically and mechanically stable. Quasiparticle band structures reveal direct gaps in the near-infrared to visible range, with gap values increasing systematically from semilocal to hybrid exchange treatments. Optical spectra computed using a tight-binding Bethe-Salpeter approach demonstrate pronounced excitonic resonances arising from reduced dimensionality and weak dielectric screening. The exciton binding energies reach 152 meV in the 1T phase and 126 meV in the 2H phase, reflecting enhanced quantum confinement in the structurally denser phase. Our results identify Y2TeO2monolayers as a rare class of stable, direct-gap MOenes with strong excitonic effects, providing a platform for exploring many-body physics in low-dimensional oxychalcogenide systems especially for photovoltaic applications.

Figures (7)

• Figure 1: Block diagram steps and computational tools employed for the investigated 1T and 2H Y2TeO2 monolayers.
• Figure 2: Structural models of the Y2TeO2 monolayers. Panels (a) and (b) show the top and side views of the Y2TeO2-1T phase, while panels (c) and (d) display the corresponding views for the Y2TeO2-2H phase. Y, Te, and O atoms are represented by golden-brown, silver-green, and red spheres, respectively.
• Figure 3: Phonon dispersion relations and thermodynamic properties of the Y2TeO2 monolayers. Panels (a) and (c) show the phonon dispersion curves of the Y2TeO2-1T and Y2TeO2-2H phases, respectively, calculated at the PBE level. Panels (b) and (d) display the temperature dependence of the Helmholtz free energy $F(T)$, entropy $S(T)$, and heat capacity at constant volume $C_v(T)$ for the corresponding monolayers.
• Figure 4: Polar plots of the in-plane mechanical properties of the Y2TeO2 monolayers: (a) Young’s modulus $Y(\theta)$, (b) shear modulus $G(\theta)$, and (c) Poisson’s ratio $\nu(\theta)$ for the 1T and 2H phases. The nearly isotropic angular dependence reflects the hexagonal symmetry and mechanical robustness of both structures.
• Figure 5: Electronic band structures and density of states of the Y2TeO2 monolayers. Panels (a) and (c) show the electronic band structures of the Y2TeO2-1T and Y2TeO2-2H phases, respectively, calculated at the PBE level (black lines) and with the HSE06 hybrid functional (colored lines). Panels (b) and (d) display the corresponding total density of states (TDOS) and projected density of states (PDOS), decomposed into contributions from Y $d$, Te $p$, and O $p$ orbitals. The Fermi level is set to zero energy.