The laboratory record power conversion efficiencies (PCE) of single junction solar cells are getting closer and closer to the theoretical Shockley-Queisser limit, specifically the Auger limit of 29.4% for crystalline silicon (c-Si) . Strong research efforts are currently devoted to the development of tandem solar cells combining a high bandgap semiconductor for the top cell with a c-Si bottom cell. The recent high PCE, higher than 19%, obtained with single junction organic solar cells makes this technology credible to be associated with c-Si in a tandem configuration. We present here the first steps in the development of organic/silicon tandem solar cells in a 3-terminal architecture . This design consists in combining an interdigitated back contact (IBC) n-type silicon bottom cell with an n-i-p organic top cell. It offers the advantages of suppressing the constraints of photocurrent matching and of the tunnel junction between both subcells, both required in a 2- terminal tandem cell. Early studies were devoted to optimize an organic single junction cell with an active layer made of the wide bandgap non-fullerene acceptor GS-ISO and PBDB-T-2F as donor polymer.. In order to optimize the organic cell, we developed a ternary blend using F8T2 as additive. This strategy led to the increase of the fill factor (FF) by decreasing the recombination in the active layer and PCE up to 10% was achieved with 1.15 V as Voc. We performed the characterization (optical, electrical, morphology) of the active layer and correlated them to the device performance. These experimental results were also used as inputs to develop a realistic numerical model of the organic cells. One of the main objectives of numerical modelling is to simulate the full 3-terminal tandem device for a better understanding of band engineering, optical transmission and transport dynamics at the interface between both subcells. Indeed, the interface between the silicon and the organic subcells is one of the key points of the tandem cell integration. We compare the results obtained experimentally and from simulation for the single organic cells. These results give first insights for the interface optimization between organic cells deposited on n-doped c-Si substrates passivated with different interface layers.