[23a-C105-1~11] 12.3 Functional Materials and Novel Devices

▲ [23a-C105-8] Unusual THz-wave absorptions in δ/α-mixed-phase FAPbI₃ single crystals: Interfacial phonon vibration modes

〇Min-Cherl Jung¹, Inhee Maeng², Seungjun Lee³, E.Q. Han⁴, Yurou Zhang⁴, Seung Jae Oh², Masakazu Nakamura⁵, Jung-Ho Yun⁴, Lianzhou Wang⁴, Young-Kyun Kwon³ (1.Univ. of Tsukuba, 2.Yonsei Univ., 3.Kyung Hee Univ., 4.Univ. of Queensland, 5.NAIST)

Keywords:organic-inorganic hybrid perovskite, FAPbI3 single crystal, Interfacial phonon vibration mode

The terahertz (THz)-wave absorption properties in organic-inorganic hybrid perovskite (OHP) materials are investigated with the in-depth development of OHP-based THz applications. In the THz range from 0.5 to 3 THz, OHPs typically show several interesting phonon modes such as transverse, longitudinal, and halogen self-vibrations. To modulate these frequencies, the density changes in defect-incorporated structures and element mixtures were tested and confirmed. In the literature, the origin of phonon modes in OHP materials have been mostly explained. However, we found new phonon vibration modes in formamidinium (FA)-based hybrid perovskite structures. FAPbI₃ single crystals, organic-inorganic hybrid perovskites, of the δ-, δ/α-mixed-, and α-phases were prepared. We intriguingly found that the δ/α-mixed-phase exhibited significant THz-wave absorption peaks at 2.0 and 2.2 THz that were not related to any phonon modes from either the δ- or α-phases, although the δ/α-mixed-phase sample was confirmed to be formed by a physical combination of the δ- and α-phases without the creation of any new chemical states. (Fig. 1) Our theoretical study performed with ab initio calculations explains these unusual THz-wave absorption behaviors; they originate from the novel vibration modes excited at the seamless interfaces in the mixed phase of FAPbI₃.