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.

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

Over the past decade, lead halide perovskites (LHPs) have emerged as new promising materials in the fields of photovoltaics and light emission due to their facile syntheses and exciting optical properties. The enthusiasm generated by LHPs has inspired research in perovskite-related materials, including the so-called "zero-dimensional cesium lead halides", which will be the focus of this Perspective. The structure of these materials is formed of disconnected lead halide octahedra that are stabilized by cesium ions. Their optical properties are dominated by optical transitions that are localized within the individual octahedra, hence the title "'zero-dimensional perovskites". Controversial results on their physical properties have recently been reported, and the true nature of their photoluminescence is still unclear. In this Perspective, we will take a close look at these materials, both as nanocrystals and as bulk crystals/thin films, discuss the contrasting opinions on their properties, propose potential applications, and provide an outlook on future experiments.

Systematic study of the relationships between energy levels of (Tl+)2, (In+)2, (Ga+)2 dimer centers and the crystalline environment

In this paper, we present the first systematic study of correlations between energy levels of (Tl+)2, (In+)2, and (Ga+)2 dimer centers and the crystalline environment by using dielectric theory of chemical bonding for complex crystals. Our model has successfully built links between the EA′, EB′, and EC′ of these centers and the environmental factor h. The h has linear relationships with EA′, EB′, and EC′. The calculated results are in good agreement with the experimental values. This model can serve as a prediction tool and can be applied to assign the absorption band energies of (Tl+)2, (In+)2, and (Ga+)2 centers.