Inverse Temperature Crystallization of Formamidinium Tin Iodide: Indirect Transition State and Restriction of Cation Motion

Abstract

Inverse temperature crystallization (ITC) growth of formamidinium tin iodide (FASnI3) is realized using γ-valerolactone (GVL) solvent, which possesses a low Gutmann acceptor number. The high-crystalline ITC-grown FASnI3 film was fabricated via a dip-coating method featuring a high-temperature substrate and a precursor solution using the GVL solvent. Transmittance measurements and photoluminescence spectroscopy revealed the presence of a narrow band gap in the FASnI3 ITC-grown film, contrasting with the band gap of a conventional single crystal and spin-coated film. Solid-state proton nuclear magnetic resonance spectroscopy demonstrated that formamidinium cations in the FASnI3 ITC-grown film were strongly bound with the SnI6 octahedron and that the motion of the formamidinium molecules was 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 band gap observed in the FASnI3 ITC-grown film was attributed to an indirect transition state induced by a Rashba splitting effect.

Growing MASnI3 perovskite single-crystal films by inverse temperature crystallization

“…To demonstrate the authenticity of the experiment, we recorded the video placed in the sup-plementary material (https://stacks.iop.org/JPCM/34/144009/ mmedia). Similar phenomena were also observed in the work of Kaneko et al [15]. They found that the precipitation was produced at 80 • C in FASnI 3 γ -valerolactone solution, but the precipitation disappeared when the temperature was heated to 180 • C.…”

“…However, the growth and preparation of Sn-based perovskite single crystals have rarely been reported. To the best of our knowledge, only MASnBr 3 (solvent is DMF) and FASnI 3 (solvent is γ -valerolactone) single crystals were reported with ITC strategy [15,16]. Therefore, further exploration of the inverse temperature phenomenon related to Sn-based perovskite is conducive to boosting the applications of Sn-based perovskite single crystals.…”

Energy Distribution in Tin Halide Perovskite

“…Notably, a dual PL emission in FASI samples has been recently reported by Sekimoto and coworkers. [ 29 ] They also attributed the phenomenon to the distribution of structural distortions by PL and NMR analysis.…”

Lights and Shadows of DMSO as Solvent for Tin Halide Perovskites

“…Sekimoto and coworkers proposed that A N (the Acceptor Number, a measure for the Lewis acid strength) might also be relevant for the tin perovskite crystallization. [43] They could obtain the inverse temperature crystallization of FASnI 3 only from γ-valerolactone, which has a low A N (13.6) and thus weakly coordinate iodide. DMSO has a relatively large A N of 19.3, compared to the value of 16.0 for DMF, thus reducing the iodide activity.…”