Modulating crystal growth of formamidinium–caesium perovskites for over 200 cm2 photovoltaic sub-modules

Upscalable fabrication of efficient and stable perovskite solar modules is urgently needed for commercialization. Here we introduce methylammonium chloride additives in the co-solvent system of N-methyl-2-pyrrolidone/N,N-dimethylformamide to control the formation of intermediate phases during the growth of formamidinium–caesium lead triiodide perovskite films. We achieve high-quality films upon drying without the use of anti-solvent. By implementing bulk and surface passivation, champion efficiencies of 24.02% for a small-sized solar cell and 20.5% for a 5 cm × 5 cm solar mini-module on an aperture area of 22.4 cm2 (geometric fill factor ∼ 96%) are achieved by spin-coating. The fully blade-coated perovskite solar sub-module demonstrates a champion efficiency of 15.3% on an aperture area of 205 cm2. The solar mini-module exhibits impressive operational stability with a T80 lifetime of over 1,000 h at maximum power point tracking under continuous light illumination. Upscaling perovskite solar cells requires control of the crystallization of perovskite films over large areas. Here, the authors tailor the composition of the precursor ink and achieve 15.3% efficient solar cells over a 205 cm2 area without the use of anti-solvent.