Tellurium Doping and the Structural, Electronic, and Optical Properties of NaYS2(1- x)Te2 x Alloys

Lahcene Azzouz; Mohamed Halit; Zoulikha Charifi; Chérif F Matta

doi:10.1021/acsomega.9b01330

Tellurium Doping and the Structural, Electronic, and Optical Properties of NaYS_{2(1- x)}Te_{2 x} Alloys

ACS Omega. 2019 Jun 28;4(6):11320-11331. doi: 10.1021/acsomega.9b01330. eCollection 2019 Jun 30.

Authors

Lahcene Azzouz^{1

2}, Mohamed Halit¹, Zoulikha Charifi^{3

3}, Chérif F Matta^{2

4}

Affiliations

¹ Laboratoire Physique des Matériaux, Université Amar Telidji, BP 37G, Laghouat 03000, Algeria.
² Department of Chemistry and Physics, Mount Saint Vincent University, Halifax, Nova Scotia B3M 2J6, Canada.
³ Department of Physics, Faculty of Science and Laboratoire Physique et Chimie des Matériaux, University of M'sila, 28000 M'sila, Algeria.
⁴ Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.

Abstract

New ternary and quaternary NaYS_2(1-x)Te_2x alloys (with x = 0, 0.33, 0.67, and 1) are proposed as promising candidates for photon energy conversion in photovoltaic applications. The effects of Te doping on crystal, spectral, and optical properties are studied within the framework of periodic density functional theory. Increasing Te content decreases the band gap (E _g) considerably (from 3.96 (x = 0) to 1.62 eV (x = 0.67)) and fits a quadratic model (E _g(x) = 3.96-6.78x + 4.70x ², (r ² = 0.96, n = 4)). The band gap of 1.62 eV makes the NaYS_0.67Te_1.33 alloy ideal for photovoltaic applications for their ability to absorb in the visible segment of the sunlight spectrum. The calculated exciton binding energies are 9.78 meV for NaYS_1.33Te_0.67 and 6.06 meV for NaYS_0.67Te_1.33. These values of the order of the thermal energy at room temperature suggest an easily dissociable hole-electron pair. The family of NaYS_2(1-x)Te_2x alloys are, therefore, promising candidates for visible photocatalytic devices and worthy of further experimental and theoretical investigations.