Today, single junction silicon technology dominates the photovoltaic (PV) market, with more than 90% of market share. However, the power conversion efficiency of silicon solar cells is now close to the theoretical limit. Indeed, the record has been pushed to 26.7 %, which is close to the silicon single junction theoretical limit of approximately 29% when the unavoidable Auger recombination is taken into account. To increase solar cell efficiency above 30% while keeping the abundant, cheap and stable silicon material as a basis, one solution is to couple silicon with another semiconductor having a larger bandgap in a tandem cell configuration. Currently, silicon based tandem technology follows two paths: the monolithic two terminals tandem (2TT) where the top and the bottom sub-cells are electrically and optically connected, and the four terminals tandem (4TT) where the two sub-cells are electrically independent. However, the 2TT architecture needs to manage photocurrent matching and to optimize the tunnel junction charges transport mechanisms between the top and the bottom sub-cells, while the 4TT device has to deal with issues related to the buried contacts shadowing and access and losses induced by the adhesive interconnection. The THESIS proposal aims at developing an original 3 terminals tandem solar cell (3TT). The approach is threefold: - To propose a new solar cell technology with 3 terminals. This allows us to suppress the constraint of photo-current matching for the two cells constituting the tandem cell. Furthermore, a 3-terminal tandem cell does not need a tunneling junction. - To facilitate the access to the different contacts of the top and bottom cells without the need for etching and without having to align buried contact grids, - To combine the advantages of reliable and mastered silicon technology with those of emerging technologies, allowing the creation of a heterojunction stack with the silicon. This new 3-terminals tandem cell technology we have patented is made possible in an innovative and simple way by using a silicon PV cell with interdigitated back contacts (IBC) on the rear face as a bottom sub-cell and depositing a larger bandgap semiconductor on top of the c-Si surface with a selective band offset barrier (BOB) at the interface in order to form a front heterojunction stack (FHS) realizing a top heterojunction sub-cell. This barrier is chosen so that the heterojunction allows a separation of the operation of the two cells. In the THESIS project, we propose to focus on the emerging perovskites as the absorber of the p-type FHS. The interface between the perovskite and silicon will be actively studied in the project and will need deep investigations to improve the interface quality and device operation. We plan to use also p/i a-Si:H stack as the FHS, forming a (p) a-Si:H/ (i) a-Si:H/ (n) c-Si vertical front subcell. Of course, we do not expect the best photovoltaic performances with this subcell due to the limited transport properties of a-Si:H. However, the growth of device quality a-Si:H for the top subcell, and the c-Si IBC technology are already well mastered in the consortium, so this will allow us to fabricate a proof of concept device for this innovative 3TT architecture. This will be a breakthrough in the PV world, since the 3TT architecture has never been demonstrated so far.