Figure 2: Oxygen diffusion.

(a) Isothermal gravimetric analysis plot (IGA) of CH₃NH₃PbI₃ (MAPI) and CH₃NH₃PbI₃(Cl) (MAPIC) thin films coated on non-conductive cleaned glass with 30 min of Helium soaking before oxygen exposure, where t=0 corresponds to the time at which oxygen was introduced into the system. (b,c) ToF-SIMS surface images (100 × 100 μm) of CH₃NH₃PbI₃ and CH₃NH₃PbI₃(Cl) respectively after exposure to dry air flow with no illumination, where the maximum counts (MC) and the total number of secondary oxygen ion counts (TC) are shown with the colour scales corresponding to the interval [0, MC].