fig4

Figure 4. FT-IR spectra of the (A and B) control and (C and D) target FAPbI₃ films at three stages: pristine (bottom), humidity-exposed (middle), and post-exposure annealed (top). Panels (A) and (C) show the full spectral range while panels (B) and (D) show enlarged spectra of the N-H stretching region. FT-IR: Fourier-transform infrared.