First-principles investigation of Pd-based Kesterites for optoelectronic and photovoltaic applications

In this article, we report a first-principles study of the structural, electronic, optical, and photovoltaic properties of the earth-abundant quaternary Kesterites Cu₂PdSnSe₂ (CPTSe) and Cu₂PdSnS₄ (CPTS). Dynamical and thermal stability of these compounds were assessed through phonon dispersion and ab-initio molecular dynamics (AIMD) calculations. The calculated band structures revealed that both materials are direct band gap semiconductors with gaps of 1.11 eV (for CPTSe) and 1.40 eV (for CPTS). Spin-orbit coupling (SOC) calculations reveal that the effect is limited only to minor band splitting, and the energy gap is unaffected. The valence band maximum is dominated by Cu-3d, S/Se-p, while the conduction band minimum is primarily composed of Sn-p, Sn-s, and Se-p orbitals. The inclusion of Hubbard potential U shifts the localized states below the Fermi level and improves electronic stability. Strong visible light absorptions (> 10⁴ cm^-1), high dielectric constants, and favorable refractive indices demonstrate efficient light harvesting and low optical losses. These properties suggest that Pd-based Kesterites can be good candidates for high-efficiency solar cell materials.

Electronic structure calculations were performed using density functional theory within the full-potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) and Hubbard U correction (GGA + U), along with mBJ (mBJ + U), were employed to accurately account for exchange-correlation effects and electron localization. Structure optimization and electronic properties calculations were performed for both materials. Optical properties were then calculated based on the optimized structures. Device simulations of the (FTO/WS₂/CPT(Se/S)/Spiro-MeOTAD/Mo) architecture were performed using SCAPS-1D. The CPTSe/CPTS-based device achieves an open circuit voltage (V_oc) of 0.95/1.34 V, a high short-circuit current density (J_sc) of 25.05/15.58 mAcm^-2 and a fill factor (FF) of 86.21/87.82%, resulting in a power conversion efficiency (PCE) of 20.61/18.34%. The enhanced performance is attributed to reduce antisite defects, improved cation ordering, and optimized alignment. These results established Pd-based Kesterites as promising sustainable absorber materials for highly efficient photovoltaic applications.