BA based: The precursor solutions of N=2 and N=i were prepared by mixing 120.6/0 mg of BAI, 52/104 mg of FAI, and 277 mg of PbI2 in 400 μL DMF and 100 μL DMSO. The concentration for all precursor solutions was 1.2M. The solutions were stirred at room temperature for a minimum of 2h in a nitrogen-filled glovebox. 45 μL of this solution was placed on top of the substrates. A two-step spin coating program was applied: first spinning at 1000 rpm for 10 s and then at 5000 rpm for 30 s. 100 µL of chlorobenzene was dripped 23 s after starting of the spinning routine. The films were then annealed at 150°C for 10 min.