Mechanochemical Synthesis of Sn(II) and Sn(IV) Iodide Perovskites and Study of Their Structural, Chemical, Thermal, Optical, and Electrical Properties

Abstract

Phase-pure CsSnI₃, FASnI₃, Cs(PbSn)I₃, FA(PbSn)I₃ perovskites (FA = formamidinium = HC(NH₂)₂ ⁺) as well as the analogous so-called vacancy-ordered double perovskites Cs₂SnI₆ and FA₂SnI₆ are mechanochemically synthesized. The addition of SnF₂ is found to be crucial for the synthesis of Cs-containing perovskites but unnecessary for hybrid ones. All compounds show an absorption onset in the near-infrared (NIR) region, which makes them especially relevant for photovoltaic applications. The addition of Pb(II) and SnF₂ is crucial to improve the electronic properties in 3D Sn(II)-based perovskites, in particular their charge carriers mobility (≈0.2 cm² Vs⁻¹) which is enhanced upon reduction of the dark carrier conductivity. Stokes-shifted photoluminescence is observed on dry powders of Sn(II)-based perovskites, which makes these materials promising for light-emitting and sensing applications. Thermal stability of all compounds is examined, revealing no significant degradation up to at least 200 °C. This meets the requirements for standard operation conditions of most optoelectronic devices and is potentially compatible with thermal vacuum deposition of polycrystalline thin films.