Fluorescence images under pulsed excitation (470 nm, 40 MHz repetition rate, 0.03 μJ cm−2 per pulse) measured in nitrogen with semitransparent scanning electron microscopy (SEM) images overlaid (a) before light soaking, and after exposing the entire film to simulated sunlight (AM 1.5, 100 mW cm−2) for 60 min and leaving in the dark for (b) 21 (c) 234 and (d) 514 min (all images have the same PL intensity scale normalized to the average PL intensity in a, scale bars, 1 μm). (e) Three-colour scale image showing the regions classified as dark, intermediate (Int.) and bright (Supplementary Fig. 10). (f) Local PL enhancement and relaxation for dark (blue, enhancement of 4.9 ×), intermediate (green, enhancement of 1.6 ×) and bright (red, enhancement of 1.1 ×) regions, where the time (t) under illumination is highlighted by the yellow shaded region for −60≤t≤0 min, and t>0 show the local PL relaxation dynamics over time left in the dark. The dotted black line is the PL relaxation averaged across the whole fluorescence image.