Figure 5. Why impermeable AZO/SnO_x EELs afford stable devices.

XRD spectra of a perovskite cell based on AZO and AZO/SnO_x as EEL before and after heating in nitrogen for 6 days. (a,b) Photoemission spectra of the iodine I3d_5/2 peak for cells based on AZO and bilayered AZO/SnO_x EELs, respectively. (c) As a reference, an AZO sample stored in N₂ ambient has been used. The other measurements are for samples aged at 60 °C in nitrogen for 6 days. The open symbols represent the raw measurement data, whereas the solid lines are a result of a peak fit. The colours are defined in the figure legend. Note that the top Ag electrode was chosen to be 10 nm. Corresponding plan-view SEM image of the 10 nm Ag layer in case of the aged AZO sample. (d) Schemes of ageing and decomposition of the perovskite in case of the AZO (e) and the AZO/SnO_x samples (f). The yellow spot in the scheme of the AZO sample symbolizes the formation of PbI₂.