Figure S1. 2D pseudo-color plot of normalized emission spectra under pump fluence of 1.4 J/cm2 at different temperature for FAPbI3 starting from FAI/PbI2 (a) and FAI/PbI2+HI (b); the PL spectra are normalized at maximum intensity.
Figure S2. Photoluminescence spectra of FAPbI3 at 5 K. The spectrum is fitted with two Gaussian peaks, and the energy gap between the two peaks is 15 meV.
Figure S3. Streak camera data showing the time-resolved PL emission at 5 K for FaPbI3 thin films starting from (a) FAI/PbI2 and (b) FAI/PbI2+HI. PL spectra extracted after photoexcitation, showing the energy difference between two emissions. The energy difference is 18 meV for FaPbI3 thin films starting from (c) FAI/PbI2, and it is 15 meV for (d) FAI/PbI2+HI.
Figure S4. Normalized photoluminescence spectra at varied excitation power. A blue-shift in ASE has been observed when the pump power was increased from 28 nJ/cm2 to 6.7 J/cm2.