<p>Double-perovskite Cs₂AgBi_1−<i>y</i>Sb_yBr₆ is a promising lead-free material for solar cells, owing to its compositionally tunable bandgap and robust stability in humid, ambient conditions. However, its power conversion efficiency remains lower than that of conventional lead-based perovskites. In this study, we systematically investigate strategies for efficiency enhancement in indium tin oxide (ITO)/TiO₂/Cs₂AgBi_1−<i>y</i>Sb_yBr₆/CuSbS₂/Au solar cell devices using SCAPS-1D simulations. Two principal approaches are pursued: the optimization of charge transport materials and the engineering of graded light absorber layers. For the first approach, we examine 17 candidate materials—eight electron transport layers (TiO₂, ZnO, WS₂, SnS₂, SnO₂, indium gallium zinc oxide [IGZO], CeO, and AlZnO) and nine hole transport layers (Spiro-OMeTAD, CuSbS₂, CuO, CuI, MoO₃, copper ferrite tin sulfide [CFTS], NiO, CuSCN, and Cu₂O)—identifying TiO₂ and CuSbS₂ as the most effective for electron and hole transport, respectively. For the second approach, we compare non-graded, linearly graded, and parabolically graded Cs₂AgBi_1−<i>y</i>Sb_yBr₆ absorber configurations. Under simulated conditions of bulk defect density of 10¹⁵&#xa0;cm⁻³, interface defect density of 10¹⁴&#xa0;cm⁻², temperature of 300&#xa0;K, and series/shunt resistance of 2 Ω·cm⁻² and 10⁴ Ω·cm⁻², the linearly graded device achieves short-circuit current of 14.15 mA cm⁻², open-circuit voltage of 1.48&#xa0;V, fill factor of 88.66%, and efficiency of 18.61%, while the non-graded device yields 10.13 mA cm⁻², 1.59&#xa0;V, 87.90%, and 14.24%, and the parabolically graded device delivers 13.48 mA cm⁻², 1.48&#xa0;V, 88.89%, and 17.77%, respectively. Notably, as the temperature decreases from 600&#xa0;K to 200&#xa0;K, the efficiency of the linearly graded device increases from 10% to 20.6%. This study advances the understanding and performance of double-perovskite-based solar cells.</p> Graphical Abstract <p></p>