First-principles and device-level investigation of a novel double halide perovskite solar cell for sustainable energy applications.

Double perovskites (DPs) have emerged as promising materials for energy and optoelectronics applications due to their structural stability and tunable properties. In this work, Na2AgRhBr6 is systematically investigated through density functional theory (DFT) and device-level simulations using COMSOL Multiphysics. The material exhibits excellent structural stability with a lattice constant of 10.67 Å, tolerance factor of 0.73, octahedral factor of 0.59, and negative formation energy of 1.64 eV per atom. Mechanical robustness is confirmed by bult (1.39 GPa), shear (12.96 GPa), and young's modulus (29.29 GPa), while thermal stability is supported by a Debye temperature of 187.74 K. Optically, it shows a direct bandgap of 1.42 eV, high absorption coefficient (4.1 × 105 cm-1), and favorable optical conductivity. A ZnO/Na2AgRhBr6/Spiro-OMeTAD solar cell is further designed and optimized using COMSOL Multiphysics. The device achieves a maximum efficiency of 28.83%, short-circuit density of 29.70 mA cm-2. Fill factor of 84.65%, and power output of 288.37 W m-2. Performance enhancement is strongly influenced by absorber thickness, doping temperature, and hole transport layer optimization. These findings highlight Na2AgRhBr6 as a highly efficient and stable candidate for next-generation photovoltaic applications.