The inverse structure triple cation mixed halide perovskite devices were prepared following a previously reported procedure. In brief, a hole transporting layer (HTL) of NiOx was first deposited on a FTO collated glass substrate by spin coating a solution of Ni(NO3)•6H2O (1 M), and ethylenediamine in EG (1 M), and was then annealed at 373 K for 30 min. A second hole transporting layer was deposited over the NiOx by spin coating a F4TCNQ doped PTAA solution inside a N2 filled glove box. A perovskite layer was then deposited on top of the HTLs. For this purpose, a cesium formamidinium methylammonium (CsFAMA) perovskite precursor solution was first prepared by adding a solution of FAMA0.22Pb1.32I3.2Br0.66 (1000 L) to DMF (510 L), DMSO (340 L) and 1-methyl-2-pyrrolidone (150 L), and then adding CsI in DMSO (1.5 M, 48 L). The perovskite layer was then deposited over the PTAA layer using a two-step spin coating process, first for 10 s at 1000 rpm, followed by 35 s at 6000 rpm. Chloroform was used as the antisolvent for the final 7 sec before the end. Afterwards, the PVK layer was annealed at 373 K for 30 min. Subsequently, a [6,6]-phenyl C61 butyric acid methyl ester (PCBM; 35 mg mL -1 in chlorobenzene) solution was spin coated on top of the perovskite layer at 3000 rpm for 45 sec as an electron transport layer (ETL). A PEIE film layer was then deposited over the PCBM coated perovskite device using a precursor solution (3.9 L mL -1 solution in isopropanol), which helps in stopping the interfacial degradation. Finally, a 100 nm conductive Ag layer was deposited over the PEIE layer using metal evaporation technique through a patterned mask, ensuring an active perovskite surface area of ~0.5 x 0.5 cm 2 .