Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics

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 MAPbI₃ perovskite films, such as 100 cm² on glass/fluorine-doped tin oxide (FTO) and 600 cm² 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 MAPbI₃), 17.18% (mesoscopic MAPbI₃) and 16.89% (planar Cs_0.05MA_0.2FA_0.75PbI₃) in the standard FTO/c(m)-TiO₂/perovskite/spiro-OMeTAD/Au architecture.