Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of upscaling. Here we present unique advantages of reactive polyiodide melts for solvent- and adduct-free reactionary fabrication of perovskite films exhibiting excellent quality over large areas. Our method employs a nanoscale layer of metallic Pb coated with stoichiometric amounts of CH3NH3I (MAI) or mixed CsI/MAI/NH2CHNH2I (FAI), subsequently exposed to iodine vapour. The instantly formed MAI(3(L)) or Cs(MA,FA)I-3(L) polyiodide liquid converts the Pb layer into a pure perovskite film without byproducts or unreacted components at nearly room temperature. We demonstrate highly uniform and relatively large area MAPbI(3) perovskite films, such as 100 cm(2) on glass/fluorine-doped tin oxide (FTO) and 600 cm(2) on flexible polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. As a proof-of-concept, we demonstrate solar cells with reverse scan power conversion efficiencies of 16.12% (planar MAPbI(3)), 17.18% (mesoscopic MAPbI(3)) and 16.89% (planar Cs(0.05)MA(0.2)FA(0.75)PbI(3)) in the standard FTO/c(m)-TiO2/perovskite/spiro-OMeTAD/Au architecture.