The characteristics of a lead-free all perovskite tandem solar cell (P-TSC) are studied in this study. All P-TSCs were developed with the goal of breaking through the theoretical power conversion efficiency (PCE) limit for single-junction (SJ) perovskite solar cells (PSCs) established by Shockley and Queisser. Solving the toxicity problem in lead-containing sub-cells is essential for the continued growth of all P-TSCs. Here, we first present a coupled three-dimensional (3D) optical-electrical simulation of two lead-free SJ MAGeI3(Eg= 1.9 eV) and MASnI3(Eg= 1.3 eV) PSCs. The results showed that the PCE of the SJ-wide bandgap (WBG) and SJ-narrow bandgap (NBG) PSCs is 19.59% and 15.57%, respectively. Next, a two-terminal (2T) eco-friendly all P-TSC with combines these two solar cells has been designed, where the MAGeI3-PSC serves as the top sub-cell and the MASnI3-PSC serves as the bottom sub-cell. By establishing the current matching condition between two sub-cells in the 2T structure, the matched short-circuit current density (Jsc) and PCE are obtained 12.30 mA/cm^2 and 28.46%, respectively. Herein, a 299 nm-thick NBG-absorber layer and a 200 nm-thick WBG-absorber layer are required. In order to increase the matched Jsc and PCE and decrease the required NBG-absorber layer thickness, the parasitic absorption and reflection losses are minimized by selecting the best materials for the transparent conductive oxide (TCO) front contact and interconnecting (IC) layers, as well as the addition of an anti-reflection (AR) layer at the air/device interface as light management strategies. The results indicate that, under the current matching condition, improving the structure would lead to in a 76 nm reduction in the NBG-absorber layer's required thickness and a 16.44% increase in PCE. Finally, we suggested the optimized 2T non-Pb all P-TSC with a high PCE of 33.14% that is environmentally safe.
