Inverse Temperature Crystallization of Formamidinium Tin Iodide
Takeyuki Sekimoto a, Michio Suzuka a, Tomoyasu Yokoyama a, Yoshiko Miyamoto a, Ryusuke Uchida a, Maki Hiraoka a, Kenji Kawano a, Takashi Sekiguchi a, Yukihiro Kaneko a
a Panasonic Corporation, Osaka, 570-8501, Japón, Moriguchi, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Poster, Takeyuki Sekimoto, 076
Publication date: 14th October 2019

Three-dimensional perovskites are represented by the general formula ABX3, where the A site contains organic or inorganic cations such as cesium (Cs+), methylammonium (MA+; CH3NH3+), or formamidinium (FA+; HC(NH2)2+); the B site contains divalent metals such as lead (Pb2+) or tin (Sn2+); and the X site contains halide anions such as chloride (Cl), bromide (Br), or iodide (I).

We demonstrate inverse temperature crystallization (ITC) growth [1] of formamidinium tin iodide (FASnI3). The high-crystalline ITC-grown FASnI3 film was fabricated via a dip-coating method featuring a high-temperature substrate and a precursor solution.

Optical measurements (transmittance and temperature-dependent photoluminescence) revealed the presence of a narrow bandgap (1.34 eV) in the FASnI3 ITC-grown film, contrasting with the bandgap of a conventional spin-coated film [2] and single crystal [3].

Solid-state proton nuclear magnetic resonance spectroscopy demonstrated that FA cations in the FASnI3 ITC-grown film were strongly bound with the SnI6 octahedron and that the motion of the FA molecules were restricted, resulting in the stabilization of a metastable bonding state in the FASnI3 ITC-grown film.

On the basis of these results and previous reports, the narrow bandgap observed in the FASnI3 ITC-grown film was attributed to an indirect transition state induced by Rashba splitting effect.

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