Fig. 5. Enhanced perovskite stability.

a–g Contour maps depicting in-situ x-ray diffraction (XRD) analysis of perovskite materials thermally degrading whilst held at 130 °C for 9 hours. Labels indicate perovskite composition and fabrication conditions (solvent, thermal curing). Full processing conditions described in Supplementary Note 6. Molecular structures shown correspond to the volatile species detected during thermal desorption-gas chromatography-mass spectrometry (TD-GCMS) analysis of each perovskite. h Schematic highlighting advantages to perovskite material properties of solution processing via MeTHF solvent system. Visible light microscopy images of encapsulated state-of-the-art perovskite thin films after aging for 3600 hours under 85 °C, 1-sun equivalent illumination (ISOS-L-2, i-j) and 3000 hours under 85 °C, 85 % relative humidity (ISOS-D-3, k, l) conditions. Evolution under ISOS-L-2 (m) and ISOS-D-3 (n) stressing of maximum power tracked efficiency (η_mpp) measured periodically on p-i-n PSCs employing 2D precursor phase-engineered FAPbI₃ (7 cells and 8 cells, respectively) and FA_0.83Cs_0.17Pb(I_0.9Br_0.1)₃ (8 cells, under each condition, “FACs”) as the photoactive layer. Cells undergoing ISOS-L-2 are encapsulated with a 250 nm layer of MoO₃ followed by an on-cell epoxy resin and cover slip. Cells undergoing ISOS-D-3 are encapsulated in glass-glass laminates employing an industry standard butyl-rubber edge sealant (described in Supplementary Note 10). Dashed lines show the median t₈₀ η_mpp values for each dataset. The median, range and interquartile range of each dataset are shown, as well as each data point within them.