A New Perspective and Design Principle for Halide Perovskites: Ionic Octahedron Network (ION).

The metal halide ionic octahedron, [MX6] (M = metal cation, X = halide anion), is considered to be the fundamental building block and functional unit of metal halide perovskites. By representing the metal halide ionic octahedron in halide perovskites as a super ion/atom, the halide perovskite can be described as an extended ionic octahedron network (ION) charge balanced by selected cations. This new perspective of halide perovskites based on ION enables the prediction of different packing and connectivity of the metal halide octahedra based on different solid-state lattices. In this work, a new halide perovskite Cs8Au3.5In1.5Cl23 was discovered on the basis of a BaTiO3-lattice ION {[InCl6][AuCl5][Au/InCl4]3}8-, which is assembled from three different ionic octahedra [InCl6], [AuCl6], and [Au/InCl6] and balanced by positively charged Cs cations. The success of this ION design concept in the discovery of Cs8Au3.5In1.5Cl23 opens up a new venue for the rational design of new halide perovskite materials.

Ligand-Free Processable Perovskite Semiconductor Ink.

Traditional covalent semiconductors require complex processing methods for device fabrication due to their high cohesive energies. Here, we develop a stable, ligand-free perovskite semiconductor ink that can be used to make patterned semiconductor-based optoelectronics in one step. The perovskite ink is formed via the dissolution of crystals of vacancy-ordered double perovskite Cs2TeX6 (X = Cl-, Br-, I-) in polar aprotic solvents, leading to the stabilization of isolated [TeX6]2- octahedral anions and free Cs+ cations without the presence of ligands. The stabilization of the fundamental perovskite ionic octahedral building blocks in solution creates multifunctional inks with the ability to reversibly transform between the liquid ink and the solid-state perovskite crystalline system in air within minutes. These easily processable inks can be patterned onto various materials via dropcasting, spraying or painting, and stamping, highlighting the crucial role of solvated octahedral complexes toward the rapid formation of phase-pure perovskite structures in ambient conditions.