Improved Performance of Lead‐Free CsGeI ₃ Perovskite Solar Cell With 2D Materials: GW Calculation and SCAPS‐1D Guided Design and Optimization

ABSTRACT Substituting lead in perovskite materials with non‐toxic elements offers a more sustainable, environmentally safe pathway for photovoltaic technologies. However, lower power conversion efficiency and stability remain challenges in the commercial development of lead‐free perovskite‐based solar cells. Here, we investigate a novel lead‐free Ge‐based halide perovskite‐based solar cell architecture through incorporating emerging 2D materials to enhance photovoltaic performance. We first use Green‐function‐based, single‐shot G0W0‐BSE simulations to predict the electronic and optical properties of a CsGeI 3 perovskite, overcoming the inaccuracies of density‐functional simulations. Furthermore, we examined the photovoltaic performance of the CsGeI 3 solar cells with and without 2D materials using SCAPS‐1D. The optimized device with integrated 2D MoS 2 and ZnS at the CsGeI 3 /transport‐layer interfaces shows excellent performance, with a PCE of 31.92%, a V oc of 1.39 V, a J sc of 28.48 mA/cm 2 , and an FF of 80.11%, compared with the device without 2D materials. Moreover, quantum efficiency analysis indicates that incorporating 2D materials extends the photon absorption range from ∼750 to 1050 nm, thereby enhancing the device's light‐harvesting capability. The enhanced performance of the solar cell is attributed to broadened spectral absorption and cascade energy‐level alignment with 2D materials. These results provide a viable pathway toward high‐performance and sustainable photovoltaic applications.