Figure 4. Particle size effects.

(a–c) Surface SEM images of small (sample 1), medium (sample 2) and large (sample 3) crystal sizes of CH₃NH₃PbI₃. (d) Normalized absorbance decay at 750 nm for methylammonium lead iodide of sample 1 (small crystals, 100 nm), sample 2 (medium crystals, 150 nm) and sample 3 (large crystals, 250 nm) with degradation conditions of illumination (25 mW cm⁻²) and dry air. (e) Superoxide yield plot for CH₃NH₃PbI₃ (with small (black), medium (red), large (blue) crystal sizes and a toluene dripped prepared sample (green) and CH₃NH₃PbI₃(Cl) (brown).