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 10(5) cm(-1) and has a relatively large dielectric constant (epsilon(xx)(st) = epsilon(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.