Optimizing tandem solar cells efficiency through current matching technique in lead-free perovskite/c-Si and lead-free perovskite/CIGS absorbers: Optimizing tandem solar cells efficiency: N Shrivastav et al.

Lead halide hybrid solar cells have demonstrated exceptional performance in recent years, but concerns over their toxicity and instability have spurred the development of perovskite-based cells without lead. This work explores a lead-free perovskite material consisting of cesium tin-germanium triiodide solid solution perovskite (CsSn_0.5Ge_0.5I₃) is utilized to fabricate solar cells with varying thicknesses and donor densities of the absorber layer. The results imply that enhancing the thickness of the layer boosts the power conversion efficiency (PCE) by facilitating better photon absorption. However, this increase in thickness also causes a reduction in both the open-circuit voltage (V_OC) and fill factor (FF). In other words, while thickening the layer improves PCE through increased photon absorption, it also negatively impacts other key performance metrics, such as V_OC and FF. Conversely, the effect of donor density (N_d) on the cell's performance is less significant than the CsSn_0.5Ge_0.5I₃ layer's thickness. This study sheds light on the critical role of thickness and donor density in optimizing the performance of CsSn_0.5Ge_0.5I₃-based solar cells. The performance of c-Si and CIGS-based single junction bottom cells under standalone conditions is also analyzed using JV and EQE curves. The C-Si-based single junction solar cell exhibited greater efficiency (21.28%) in converting photons of different wavelengths into electrons compared to the CIGS-based solar cell (16.26%). Lastly, for increasing the PCE of the single-junction solar cells the study moves towards multi-junction solar cells. In this context, two highly efficient TSCs (LFPVK/c-Si and LFPVK/CIGS) are designed and analyzed using the current matching technique, which involves the series connection of the top and bottom cells with increased PV parameters (LFPVK/c-Si-J_SC: 21.44 mA/cm², V_OC: 1.45 V, FF: 82.17%, PCE: 25.54% and LFPVK/CIGS-J_SC: 21.83 mA/cm², V_OC: 1.33 V, FF: 73.34%, PCE: 21.45%). [ABSTRACT FROM AUTHOR]