Intrinsically Stable Wide Band Gap Br-Free CsxFA1-xPbI3 (x=0.5-0.9) Perovskites Overcoming Phase Segregation

A ~20 nm thick compact TiO₂ was deposited on patterned FTO (TEC-7) by spray pyrolysis of 0.2 M Ti (IV) bis(ethylacetoacetate)-diisopropoxide 1-butanol solution at 450 ºC followed by annealing at 450 ºC for one hour. The perovskite precursor solution was prepared by dissolving CsI, FAI, PbI₂ and DMAI in 1 mL DMF and was deposited on 70 ℃ preheated c-TiO₂/FTO substrate by spin coating at 3000 rpm for 30 s. The obtained precursor film was annealed at 170℃ for 40 min. A hole-transport material (HTM) solution containing 0.1 M spiro-OMeTAD, 0.035 M Li-TFSi, and 0.12 M 4-tert-butylpyridine (tBP) in chlorobenzene solution was then spin coated onto the perovskite film at 4000 rpm for 20 s. Finally, a 100 nm thick Ag was deposited as contact layer via thermal evaporator.