Fig. 5: Heterogeneity in photoluminescence emission.

Hyperspectral luminescence of perovskite thin films with compositions. a–d {x/y} = 0.25|0.40. e–h {x/y} = 0.75⁞0.40. i–l {x/y} = 0.75⁞0.50. Here, 2D emission maps in a, e, and i represent the wavelength at emission maximum for pristine films. 2D maps in b, f, and j show the wavelength change (Δλ) upon continuous illumination (450 nm, 5 min). Spectra in c, g, and k are averaged over the scanned area of pristine (red line) and illuminated (blue shaded) films. d, h, and l show histogram of maximum emission wavelengths in pristine (red) and illuminated (blue) thin films. The maps show that emission heterogeneity increases with increasing MA and Br content and that in rough films, regions of low-energy emission undergo a smaller redshift after continuous illumination. Note the different color scales in (a, e, and i) and in (b, f, and j).