Comprehensive Investigation of Structural, Mechanical, Optical, Thermoelectric Properties, and Photovoltaic Performance of Lead-Free Novel Li2PdCl6 and Na2PdCl6 Using DFT and SCAPS-1D Simulation

Abstract

This study presents a detailed first-principles investigation of lead-free double perovskites Li2PdCl6 and Na2PdCl6 to evaluate their suitability for high-efficiency solar cell applications. Using Density Functional Theory (DFT) and SCAPS-1D simulations, we explored their structural, electronic, optical, mechanical, thermoelectronic, and photovoltaic properties, along with population analysis. Both materials are structurally stable, with Na2PdCl6 exhibiting slightly greater stability based on Goldschmidt tolerance factors and formation energies. Direct band gaps are calculated as 1.195 eV (Li2PdCl6) and 1.110 eV (Na2PdCl6) using GGA-PBE, and 2.225 eV and 2.133 eV with HSE06, placing them close to the optimal range for single-junction solar cells. PDOS and charge density analyses confirm strong bonding and atomic-level contributions. Optical results reveal excellent visible light absorption and low reflectivity. Mechanically, Li2PdCl6 is more ductile, while Na2PdCl6 is stable yet brittle. Anisotropy indices suggest both are mechanically reliable. Thermoelectronic analysis shows good temperature-dependent heat capacity, debye temperature, thermodynamically stable and raman effect, supporting their potential in optoelectronic devices. Population analysis validates electronic behavior and bonding characteristics. Photovoltaic performance was assessed using SCAPS-1D by varying absorber layer thickness, defect densities, and shallow acceptor concentrations across different temperatures. Na2PdCl6-based devices exhibit superior performance, achieving a PCE of 25.55%, JSC of 42.55 mA/cm2, FF of 79.16%, and VOC of 0.758 V. In comparison, Li2PdCl6 attains a PCE of 23.06%, JSC of 38.12 mA/cm2, FF of 76.97%, and VOC of 0.786 V. Na2PdCl6 also exhibits better defect tolerance and thermal stability. Overall, Na2PdCl6 emerges as a promising, eco-friendly material for next-generation solar cells, with Li2PdCl6 offering a strong alternative.