To continue to follow the long-term learning curve of ca. 0.5%absolute per year for industrial silicon solar cells, innovation is needed to allow for conversion efficiencies beyond its physical limit of 29.4%. Multi-junction solar cells that encompass silicon and perovskite subcells offer a very promising option to continue the needed efficiency increase for industrial solar cells for the next decades. The scope of this project thus is the development of a highly efficient but simple and resource-saving Si subcell for a 2-terminal perovskite/Si tandem solar cell. The subcell to be developed within this project encompasses the recombination contact as well as the hole contact layer, which represents the transition from the Si to the perovskite cell. The Si subcell utilizes both sides passivating contacts based on poly-Si/SiOx, which have a passivation performance such that it allows for the highest efficiencies. In addition to the increase in efficiency and the resulting cost benefits, the topic of sustainability will also be directly addressed in the project. “Cast mono” silicon wafers, which are a low CO2 silicon base material will be investigated as an alternative for the standard Czochralski (Cz) silicon wafers for the fabrication of the silicon bottom cell. Furthermore, particular attention will be given to the application of contact layers such as the recombination junction and the hole transport layer, that do not contain rare elements such as Indium.