First principles investigation of electronic, magnetic, optical, and mechanical properties halide double perovskites Cs₂CuMoX₆ (X = Cl, Br) for sustainable energy applications

Structural, electronic, optical, and mechanical properties of Cs₂CuMoX₆ (X = Cl, Br) double perovskites were investigated with the aid of density functional theory (DFT) calculations. However, these materials have also proved to be promising candidates for lead-free perovskite solar cells as they can exhibit tunable electronic properties and are more stable. We find that Cs₂CuMoX₆ (X = Cl, Br) has favorable structural and thermodynamic stability based on tolerance factors of 0.96 for Cs₂CuMoCl₆ and 0.95 for Cs₂CuMoBr₆, and formation energies of −2.38 eV/atom for Cs₂CuMoCl₆ and −2.42 eV/atom for Cs₂CuMoBr₆. Electronic structure calculations show that Cs₂CuMoCl₆ and Cs₂CuMoBr₆ have indirect band gaps of 1.28 eV and 1.15 eV for solar light absorption, respectively. Cs₂CuMoBr₆ shows better light absorption in the 2.5–3.5 eV range and a higher refractive index, making it ideal for solar cells. On the other hand, Cs₂CuMoCl₆ has higher reflectivity at low energies and stronger absorption at higher energies, making it more suitable for reflective coatings and optical filters. Mechanical properties analysis suggests reasonable stability, but the brittle nature of these materials raises caution regarding the fabrication of devices. Additionally, the calculated elastic constants indicate that these materials are anisotropic in their mechanical behavior and may be affected by other mechanical stresses. Overall, our findings demonstrate the great potential of Cs₂CuMoX₆ double perovskite materials for sustainable energy applications, particularly for solar cells.