Formamidinium lead iodide (FAPbI₃) emerges as one of the most promising materials for perovskite solar cells (PSCs) with high power conversion efficiency (PCE) and good stability. However, (i) the scalability lags behind and only a few reports have been dedicated so far towards the scalable processing of FAPbI₃ perovskite solar modules; (ii) FAPbI₃ has not been applied in multi-junction solar cells and the performance of perovskite–perovskite–silicon triple-junction solar cells lag considerably behind with only a limited number of reports on prototypes. First, this study reports void-free, α-phase, and high-quality FAPbI₃ thin films processed via vacuum-assisted growth (VAG) method in p-i-n-based PSCs. VAG eliminates interfacial voids at the buried interface of hole-transport layer (HTL)/FAPbI₃, enabling a high PCE of 22.3% for p-i-n-based PSCs. We demonstrate that the voids result in non-radiative recombination loss (i.e., open-circuit voltage (V_OC) loss) and poor charge extraction (i.e., low current density (J_SC)). An innovative combination of employing methylammonium chloride (MACl) as an additive and applying a moderate N₂-flow during the VAG process facilitates blade coating homogeneous large-area FAPbI₃ thin films without interfacial voids. As a result, scalable PSCs (0.105 cm²) and mini-modules (aperture area of 12.25 cm², geometrical fill factor of 96.3%) with PCEs of 20.0% and 18.3% are achieved, respectively. Second, this study addresses significant challenges in processing triple junctions in which the most critical junction is the middle perovskite sub-cell. We present triple-junction perovskite–perovskite–silicon solar cells achieving an unprecedented PCE of 24.4%. Through the optimization of light management for each perovskite sub-cell (with bandgaps of ~1.84 eV and ~1.52 eV for the top and middle cells, respectively), the current generation is maximized to 11.6 mA cm^–2. The key to this achievement is the development of a high-performance middle perovskite sub-cell, utilizing a stable pure-α-phase FAPbI₃ perovskite thin film that is free of wrinkles, cracks, and pinholes. This enables a high V_OC of 2.84 V in the triple-junction architecture. Notably, non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency when stored in the dark at 85°C for 1081 hours. These are remarkable advances in upscaling FAPbI₃-based PSCs and multi-junction PVs.