Predicting the photovoltaic and optoelectronic potentials of eco-friendly kesterites Ag2PdMX4 (M = Sn, Ge; X = S, Se) through first-principles calculations.

Silver-based kesterite chalcogenides have emerged as attractive substitutes for conventional Cu-based solar absorbers because of their reduced cation disorder, improved electronic properties, and photovoltaic potential. The kesterite compounds Ag2Pd(Sn,Ge)X4 (X = S, Se) were investigated via density functional theory (DFT) calculations and were found to be stable. The structural properties were computed using the GGA-PBEsol functional, while the electronic properties were predicted using the GGA, mBJ, GGA+U, and TB-mBJ+U approaches, confirming the direct band gap nature. The calculated band gap energy values are in the range of 1.19-1.9 eV using mBJ+U, finding them suitable for solar cell applications. Spin-orbit coupling (SOC) calculations reveal that the SOC effect is noticeable and a compound dependent reduction, because heavy atoms like Pd, Ag, Sn, and Se cause band splitting along with band reduction. The valence band maximum is contributed by Ag-4d/Pd-4d and chalcogen-p states, whereas the conduction band minimum is contributed by Sn/Ge-p states, which show strong orbital hybridization near the Fermi level. A strong absorption coefficient (∼105 cm-1), favorable optical response, and low energy loss also demonstrate excellent light-harvesting capability. Photovoltaic performance was evaluated using the SCAPS-1D simulation package, with the solar cell architecture FTO/TiO2/Ag2Pd(Sn,Ge)X4/Cu2O/Pt. Among the Sn-based compounds, Ag2PdSnS4, with its near-optimal band gap, exhibits enhanced photovoltaic performance, achieving an open-circuit voltage (V OC) of 1.22 V, short-circuit current density (J SC) of 24.43 mA cm-2, fill factor (FF) of 80%, and power conversion efficiency (PCE) of 23.8%. In the Ge-based series, Ag2PdGeSe4 exhibits the highest predicted performance with a V OC of 1.10 V, J SC of 30.37 mA cm-2, FF of 76%, and PCE of 25.3%. These results indicate that the studied kesterites are emerging environmentally friendly semiconductors for next-generation thin-film photovoltaic and optoelectronic applications.