Unique phonon modes of a CH3NH3PbBr3 hybrid perovskite film without the influence of defect structures: an attempt toward a novel THz-based application

The exploration of new physical properties for various THz-based applications, such as THz-wave sensing, modulation, and imaging devices, is a key challenge in the research on organic–inorganic hybrid perovskite materials. These THz-based applications require satisfactory, sensitive, and stable absorption properties with values between 0.5 and 3 THz. To achieve these properties, candidate materials should possess a purified structure that induces regular and fixed phonon modes without any defects or impurities. CH 3 NH 3 PbBr 3 , an organic–inorganic hybrid perovskite thin film produced by a sequential vacuum evaporation method on a flexible PET substrate, was investigated in this study. Although the thin film contains only molecular defects related to CH 3 NH 2 incorporated into the perovskite structure, our THz-wave absorption measurement and first-principles simulation confirmed that these molecular defects do not influence the three phonon modes originating from the transverse vibration (0.8 THz), the longitudinal optical vibrations (1.4 THz) of the Pb–Br–Pb bonds, and the optical Br vibration (2.0 THz). After spin-casting an ultrathin PTAA polymer protective layer (5 nm) on the hybrid perovskite thin film, it was additionally observed that there was no significant effect on the phonon modes. Thus, this novel flexible organic–inorganic hybrid perovskite material is a potential candidate for THz-based applications. NPG Asia MaterialsOptical materials: a new choice for security imaging A material useful for security imaging has been identified by an international team of scientists. Radiation between the infrared and microwave parts of the electromagnetic spectrum can pass through clothing. This so-called terahertz radiation is valuable for security screening technology as it can identify a wider range of materials than metal detectors and is much quicker than a manual pat-down. A team led by Young-Kyun Kwon from Kyung Hee University, Seoul, South Korea, and Min-Cherl Jung from the University of Tsukuba, Ibaraki, Japan, demonstrated that a material already used with great success in optoelectronic and solar cell applications, known as an organic–inorganic hybrid perovskite, also has useful terahertz properties. The team created thin films of this material on a flexible substrate and showed that it absorbed radiation at fixed terahertz frequencies. Phonon modes of CH 3 NH 3 PbBr 3 hybrid perovskite thin film.