Perovskite-Si tandem solar cells are a leading pathway to surpass the single-junction efficiency limit of crystalline silicon photovoltaics. Their realization requires integrating many functional layers, making reproducible high-performance fabrication and systematic analysis challenging. This thesis investigates the design, fabrication, and characterization of monolithic solution-processed perovskite-Si tandems, combining process development with quantitative modeling to establish practical guidelines for reproducible, high-efficiency operation and to address tandem-specific challenges beyond single-junction devices. The first chapter summarizes key aspects of tandem operation and the main methods used, focusing on currente-voltage characterization and electrical modeling. The analysis centers on the tandem fill factor (FF), whose interpretation differs from single-junction devices. Using equivalent-circuit modeling, correlations between single-junction metrics (pseudo-FF and series resistance) and tandem FF are identified, followed by experimental implications and measurement approaches, including multi-level illumination and current-mismatch analyses. Next, guidelines and a design philosophy for reproducible tandem fabrication are presented, including tandem-specific adjustments to the manufacturing environment and bottom-cell configuration, such as protective SiOx layers for durability. Key improvements to both subcells and the top electrode are then described. Two synergistic developments in the perovskite top cell are emphasized: pFBPA as an ink additive, and silica nanoparticle coatings that recover film quality and improve wettability on Me-4PACz-coated hydrophobic substrates. Together, these enabled a certified 30.9% efficient device that forms the basis of the subsequent work. The non-perovskite-specific improvements also contributed to a 31.3% record-efficiency device on fully textured Si substrates fabricated by hybrid vapor-solution processing, which is beyond the scope of this thesis. The following chapter analyzes device losses, with emphasis on FF-related contributions. Using single-junction cells and numerical modeling, the evolution of series resistance from small-area cells on glass to large-area cells on Si is quantified, revealing increases associated with illumination-side reversal and the glass-to-Si substrate transition. A method to extract the contact resistivity of the buried interface is proposed and applied, indicating that additional losses upon Si integration do not originate from this interface. Recombination, optical, and resistive losses are then quantified to identify routes for further gains. Two optical improvements are presented: a SiO2-nanoparticle-based infrared rear reflector and undulated perovskite films on pyramid-textured Si wafers, the latter providing enhanced optical performance upon encapsulation with comparable electronic quality. Combined with these and other developments, in-house efficiencies up to 33% are demonstrated. Finally, long-term stability is investigated using a newly developed accelerated-aging setup. Architectural effects are studied from single-junction perovskite cells to perovskite-Si tandems. While area upscaling reduces stability, introducing a transparent conductive oxide electrode and illuminating from the electron-transport-layer side significantly improve it, indicating a potential stability advantage of tandem devices over single-junction counterparts.