Zero-dimensional (0D) mixed-halide hybrid organic−inorganic MA 4 PbX 6 • 2H 2 O (MA = CH 3 NH 3 + ; X = Br 1 − x I x with 0 < x < 1) has been synthesized by a solvent-free mechanochemical approach. It has been shown that this 0D phase with sharp absorption features in the near-UV is a hydrated structure, which can be reversibly transformed into the three-dimensional perovskite phase MAPbX 3 by simple thermal annealing (dehydration) in air. This work reveals a new approach to hybrid organic−inorganic perovskites and related 0D structures, which have so far only been thoroughly studied for the inorganic Cs 4 PbX 6 compounds.

Thermal deposition of halide perovskites as a universal and scalable route to transparent thin films becomes highly challenging in the case of lead-free double perovskites, requiring the evaporation dynamics of multiple metal halide sources to be balanced or a single-phase precursor preliminary synthesized to achieve a reliable control over the composition and the phase of the final films. In the present Letter, the feasibility of the single-source vacuum deposition of microcrystalline Cs2Ag x Na1–x Bi y In1–y Cl6 double perovskites into corresponding transparent nanocrystalline films while preserving the bulk spectral and structural properties is shown. The perovskite films produced from the most emissive powders with x = 0.40 and y = 0.01 revealed a photoluminescence quantum yield of 85%, highlighting thermal evaporation as a promising approach to functional perovskite-based optical materials.

Most current thermoelectric materials have important drawbacks, such as toxicity, scarceness, and peak operating temperatures above 300 °C. Herein, we report the thermoelectric properties of different crystalline phases of Sn-based perovskite thin films. The 2D phase, Cs 2 SnI 4 , is obtained through vacuum thermal deposition and easily converted into the black β phase of CsSnI 3 (B-β CsSnI 3 ) by annealing at 150 °C. B-β CsSnI 3 is a p-type semiconductor with a figure of merit (ZT) ranging from 0.021 to 0.033 for temperatures below 100 °C, which makes it a promising candidate to power small electronic devices such as wearable sensors which may be interconnected in the so-called Internet of Things. The B-β phase is stable in nitrogen, whereas it spontaneously oxidizes to Cs 2 SnI 6 upon exposure to air. Cs 2 SnI 6 shows a negative Seebeck coefficient and an ultralow thermal conductivity. However, the ZT values are 1 order of magnitude lower than for B-β CsSnI 3 due to a considerably lower electrical conductivity.