Exploring the physical properties of ZnAgX3 (X = F, Cl, Br) for optoelectronic and thermoelectric applications: a DFT study

Abstract

The growing demand for efficient energy conversion and advanced optoelectronic devices has driven extensive research into multifunctional materials with tunable physical properties. In this work, we present a comprehensive first-principles investigation of cubic perovskites ZnAgX3 (X = F, Cl, Br) using density functional theory as implemented in the Quantum ESPRESSO package. The structural, electronic, optical, mechanical, and thermoelectric properties are systematically explored employing both GGA-PBE and HSE06 exchange–correlation functionals. Structural optimization confirms that all compounds crystallize in the stable cubic Pm3̅m phase, with thermodynamic stability evidenced by negative formation energies ranging from −2.109 to −1.176 eV, Goldschmidt tolerance factors of 0.891–0.848, and dynamical stability verified by the absence of imaginary phonon modes. Electronic band structure calculations reveal indirect semiconducting behavior with tunable band gaps that decrease from ZnAgF3 to ZnAgBr3. The HSE06 functional predicts band gaps of 2.857 eV, 2.503 eV, and 1.673 eV for ZnAgF3, ZnAgCl3, and ZnAgBr3, respectively. Optical analysis indicates a strong halogen-dependent response in dielectric function, refractive index, absorption, and optical conductivity, with ZnAgBr3 exhibiting the highest static dielectric constant (3.86) and absorption coefficient (∼1.70 × 106 cm−1) due to its narrower band gap. Mechanical studies have verified that all the compounds meet the Born stability requirements and that they are ductile. The calculated B/G ratios (2.88–3.07) further confirm the ductile nature of all investigated compounds. Thermoelectric analysis demonstrates a significant enhancement in performance with heavier halide substitution, with ZnAgBr3 achieving a high figure of merit (ZT = 0.98 at 300 K and ZT ≈1.96 at 1000 K), highlighting its potential for high-temperature thermoelectric applications. Overall, halogen substitution is shown to be an effective strategy for tailoring the bonding characteristics, electronic structure, and transport properties, positioning ZnAgBr3 as a promising candidate for multifunctional optoelectronic and thermoelectric devices.