Multi-functional DFT and SCAPS-1D analysis of lead-free Z2MgGeI6 (Z = Na, K) double perovskites for optoelectronic, photo-catalytic, and photovoltaic applications

In this study, first-principles calculations are used to examine the structural, electrical, optical, photocatalytic, and solar cell device characteristics of double halide perovskites Z₂MgGeI₆ (Z = Na, K). Using WIEN2k within the framework of density functional theory, the Tran-Blaha modified Becke–Johnson potential (TB-mBJ), the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), and the full-potential linearized augmented plane wave (FP-LAPW) approach are used in this investigation. Solar Cell Capacitance Simulator-one Dimension (SCAPS-1D) is utilized to check the power conversion capability of the understudy compound Z₂MgGeI₆ (Z = Na, K). Molecular dynamics computation, tolerance factor calculations, and negative formation energies were employed to evaluate thermodynamics and structural stability. Na₂MgGeI₆ and K₂MgGeI₆ have indirect semiconductor behavior, as confirmed by their computed energy band gaps of 1.475 eV and 1.483 eV, respectively. The compounds Z₂MgGeI₆ (Z = Na, K) also have remarkable optical characteristics, such as a high refractive index, a good dielectric function, a significant absorption coefficient, low reflection, and smaller effective masses and exciton binding energies, which highlight their potential applications in solar cells and optoelectronic devices. The materials under investigation exhibit photocatalytic capabilities that make them suitable candidates for hydrogen splitting and oxidation of water, potentially leading to their usage for efficient water splitting driven by solar energy. Furthermore, Z₂MgGeI₆ (Z = Na, K) is a promising option for solar energy conversion, and the material under consideration has an exceptional power conversion efficiency (PCE∼30 %).