Multiscale first-principles investigation of vacancy-ordered lead halide double perovskites for photocatalytic oxidation and high-efficiency photovoltaic applications

This study investigates the structural, electronic, optical, mechanical, anisotropic, phononic, molecular dynamics, photocatalytic oxidation and charge distribution properties of A 2 PbCl 6 (A = Li, Na, K, Rb, Cs, Fr) vacancy-ordered double perovskites using density functional theory combined with SCAPS-1D device simulations to evaluate their potential for both photocatalytic and photovoltaic applications. All compounds exhibit negative formation energies and favorable tolerance factors, indicating thermodynamic stability, while phonon dispersion confirms dynamical stability for Rb 2 PbCl 6 , Cs 2 PbCl 6 , and Fr 2 PbCl 6 materials. Direct Γ–Γ bandgaps, high absorption coefficients (~ 10 5 cm −1 ), and low reflectivity confirm excellent visible and UV light-harvesting potential. Mechanical analysis reveals that ductile compositions (K 2 PbCl 6 , Fr 2 PbCl 6 ) are suitable for flexible devices, whereas stiffer variants (Li 2 PbCl 6 ) are ideal for robust protective layers. Anisotropy assessments guide material selection for either uniform or direction-specific performance, while Mulliken and Hirshfeld population analyses confirm strong ionic bonding favorable for charge separation. The calculated band-edge positions align favorably with redox potential, indicating strong photocatalytic oxidation capability. This suggests that the studied materials can efficiently generate oxidative species, making them suitable for applications such as pollutant degradation and environmental remediation. In the SCAPS-1D modeling of Al/FTO/SnS 2 /A 2 PbCl 6 /Ni solar cell structures, absorber layer thickness, total interface defect density, and shallow acceptor/defect densities were systematically optimized. The simulated J–V parameters, QE spectra, and overall device performance demonstrate a strong dependence on the intrinsic material properties of the A 2 PbCl 6 absorbers. The calculated PCE values range from 18.721 to 26.266%, suggesting that these double perovskites possess favorable characteristics for photovoltaic operation. Overall, this study highlights A 2 PbCl 6 double perovskites as multifunctional materials with promising photocatalytic oxidation capability and high photovoltaic efficiency, offering a viable pathway toward sustainable energy and environmental applications.