Insights into the Role of Cs2CuSbCl6 and Cs2AgSbBr6 as Absorber Layers in Improving the Efficiency of Double Perovskite Solar Cells Using Density Functional Theory Integrated with Simulation Frameworks

Abstract Double perovskites (DPs) have become significant lead (Pb)-free alternatives because of their toxic-free nature and high stability compared to Pb-based PSCs. In this work, the DPs Cs2CuSbCl6 and Cs2AgSbBr6 are thoroughly investigated as possible photovoltaic (PV) materials using DFT computation and device simulation through WIEN2K and SCAPS-1D tools, respectively. First, we investigated the optoelectronic characteristics of both Cs2CuSbCl6 and Cs2AgSbBr6 through the WIEN2k tool. The computed band gaps (Eg) of Cs2CuSbCl6 and Cs2AgSbBr6 are found to be 1.64 eV and 1.89 eV, respectively. UV absorption peaks at around 13 eV are seen in Cs2CuSbCl6 and Cs2AgSbBr6, with an increase in peak magnitudes occurring at photon energies of 2.19 eV for Cs2CuSbCl6 and 2.81 eV for Cs2AgSbBr6, respectively. These findings suggest that Cs2CuSbCl6 and Cs2AgSbBr6 have strong potential as absorbers for solar cell (SC) applications. This paper compares the modeling and optimization of three types of PSC structures, including the single-junction FTO/ZnO/Cs2CuSbCl6/Spiro/Au, FTO/ZnO/Cs2AgSb6/Spiro/Au, and graded double absorber layer-based FTO/ZnO/Cs2CuSbCl6/Cs2AgSb6/Spiro/Au architecture, using a simulation method via SCAPS-1D. The proposed graded double active layer-based PSC architecture delivered improved performance as compared to the single-layered architecture. An optimized performance of a graded double active layer-based PSC architecture with a Jsc of 21.52 mA/cm2, a Voc of 1.06 V, an FF of 84.13%, and a PCE of 19.20% has been observed, while Cs2CuSbCl6- and Cs2AgSbBr6-based single-junction PSCs demonstrated PCEs of 14.64% and 17.88%, respectively. In this work, we use the SCAPS-1D modeling tool to propose and simulate a unique lead-free dual absorber layer design. This design strategy offers a feasible path to the development of highly effective, environmentally friendly, and thermally stable perovskite (PVSK) PV systems. These results can bring about significant advancement in the field of nontoxic DP technology through careful and optimized experimental design and fabrication.