Structural, Electronic, Optical, and Mechanical Properties of Cu(I)Au(III)-Based Double Perovskites: A First-Principles Study

Herein, the structural, electronic, optical, and mechanical properties of Cu(I)Au(III)-based double perovskites using first-principles calculations are investigated. Phonon calculation results confirm that pure halide Cs₂CuAuX₆ (X = Cl, Br), mixed-halide Cs₂CuAuBr₄Cl₂ and Cs₂CuAuI₄Br₂, and strained Cs₂CuAuI₆ (by 3% strain) are dynamically stable. Subsequently, the optoelectronic and mechanical properties of these compounds are calculated. The calculations reveal that Cs₂CuAuX₆ exhibits slightly indirect-bandgap semiconducting behavior, with the bandgaps of 1.169, 1.191, and 1.355 eV from the HSE06 hybrid functional for X = Cl, Br, and I, respectively. Meanwhile, the bandgap of Cs₂CuAuI₆ decreases with the increase of strain from 1% to 3% (1.271, 1.148, and 1.037 eV, respectively). In addition, the results show that Cs₂CuAuI₄Br₂ (Eg^HSE06 = 1.278 eV) has a suitable bandgap, which is close to the ideal direct bandgap. Moreover, Cs₂CuAuI₄Br₂ exhibits strong anisotropic visible light absorption with absorption coefficients exceeding 10⁵ cm⁻¹ and has a relatively large dielectric constant (ε^xx_st = ε^yy_st = 36.27) along the ab plane. Furthermore, its Pugh's ratio (Poisson's ratio) value of 2.94(0.35) exceeds the critical value of 1.75(0.26), indicating its ductility and potential for use in flexible electronic devices.