Fig. 3. (A) Schematic illustration of photoinduced halide segregation upon continuous wave light irradiation using a 405 nm diode laser (with a spot size of 0.764 cm2) and corresponding in situ spectral absorption measurement. The inset in 3A shows a digital photo taken under photoirradiation using BA film. (B) Corresponding photoinduced halide ion segregation in the 2D mixed (Br : I = 50 : 50) halide perovskite films. (C and D) Time-dependent absorption changes (C) in 2D mixed halide perovskites with BA upon CW 405 nm diode laser irradiation (100 mW cm−2) for 15 min and corresponding difference absorption (D) obtained by subtraction from the 0 min spectrum. (E) Kinetic trace and monoexponential fits by tracking the changes in Br-rich (at 408 m), mixed (at 447 nm), and I-rich (at 500 nm) domains, respectively, as shown in panel D. Note that the difference absorption spectra are obtained by subtracting the spectra recorded at longer time from the spectra at zero time.
