The effects of brief atmospheric exposure are assessed for mixed composition perovskites comprised of a combination of formamidinium tin iodide (FASnI 3 ) and methylammonium lead iodide + chloride (MAPbI 3−3x Cl 3x ) as well as MA 0.7 FA 0.3 PbI 3 perovskite for use as absorber layers in high-efficiency thin film solar cells. Photothermal deflection spectroscopy (PDS) is employed to probe the relative defect density of all films by way of extracting the Urbach energy characterizing the width of the sub-bandgap absorption tail. Exposure to atmosphere for ~3 min prior to PDS measurement is found to degrade mixed composition films such that exposed films had an average increase of 36% in Urbach energies compared to those that are fully kept out of atmosphere through immersion in inert C 6 F 14 liquid. By contrast, the same exposure to atmosphere induced no change in Urbach energy for MA 0.7 FA 0.3 PbI 3 . These results demonstrate the influence of ambient exposure on perovskites, particularly those containing Sn, and highlight the fact that handling procedure itself throughout all fabrication and subsequent characterization steps influences the measured results.

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The subsolidus phase relations of the BaO–Y2O3–MnO2 system have been investigated in air. There are eight binary compounds, a new ternary compound and 11 three‐phase regions in this system. The ternary compound with the BaO:YO1.5:MnO2 molar ratio of 8:2:5 was indexed by a rhombohedral lattice with a = 5.7929 (6) and c = 28.586 (4) Å. The synthesized compounds were determined to be stoichiometric except for the Ba1−xYxMnO3 phase (x ≤ 0.01).