A SCAPS simulation investigation of non-toxic MAGeI3-on-Si tandem solar device utilizing monolithically integrated (2-T) and mechanically stacked (4-T) configurations

In this study, solar cell capacitance simulator (SCAPS) was utilized to investigate a tandem solar device with Methyl-ammonium germanium iodide (MAGeI3), an organic perovskite, as top cell active layer, and crystalline silicon (c-Si) as the bottom cell. Validation studies were done against established single-junction device structures including MAPbI3 and c-Si. Our simulation-based results showcase a robust congruence with experimental data, with obtained power conversion efficiency (PCE) values of 20.19%, and 23.01% for MAPbI3 and c-Si based single-junction devices, respectively. For the thesis of this work, both four-terminal (4-T) and two terminal (2-T) perovskite-on-silicon tandem architectures were investigated. Our numerical simulation for the monolithic stacked 2-T tandem structure of MAGeI3-on-c-Si produced a PCE of 28.71 %, while a PCE of 32.2 % was obtained for the standard MAPbI3-on-c-Si. For the current matching condition in the 2-T tandem devices, the optimum thickness of MAGeI3 and MAPbI3 were found to be 626 nm and 223 nm respectively. For the mechanically stacked 4-T configurations, MAGeI3-on-c-Si and MAPbI3-on-c-Si produced PCE values of 29.85 % and 33.67%, respectively, with optimum top cell absorber thickness values of 1.7 µm and 1.4 µm, respectively. Each device architecture was optimised by carrying out extensive studies including modulations in absorber thickness, bulk defect density, interfacial defect density, and back contact metal work function. Our in-depth analyses highlight a remarkable potential for MAGeI3 to be utilized as the top cell of a perovskite-on-silicon solar device, boasting high efficiency and intrinsic non-toxicity.