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The flexible and mixed δ-and α-formamidinium lead iodide (FAPbI 3) hybrid perovskite thin films fabricated by the sequential vacuum evaporation method (SVE) were studied using the THz-wave absorption property. The formed FAPbI 3 using SVE showed the typical δ-phase. After annealing for 10 min, we confirmed a mixed state with δ-and α-phases and observed THz-wave absorption at 1.62 THz with 40% absorptance. In the C 1s core-level spectra, we found two different chemical states originated from δ-and α-FAPbI 3. The origin of the THz-wave absorption property is assumed from a significant Pb–I vibration mode from the mixed phases in FAPbI 3.