Halide perovskites have attracted tremendous attention from many researchers recently, particularly for their excellent optoelectronic properties in applications such as photovoltaic solar cells and light-emitting diodes. In recent years, the application of halide perovskites has rapidly extended into nanoelectronics, such as thermoelectric, memory, and artificial synapse applications. Halide perovskites can be synthesized easily, even at relatively low temperatures, and organic and inorganic ions can even coexist in one crystal structure. Moreover, the structural flexibility is excellent, where two- and three-dimensional crystals can be linked together. The combination of various types of halide ions not only controls the physical properties of the halide perovskite, but also facilitates control of the bandgap by varying the size of nanoparticles when they exhibit quantum effects. Halide perovskites thus provide an excellent platform for optoelectronics with interesting optical, electrical, and magnetic properties. The articles in this issue introduce the wide range of basic properties and potential applications of halide perovskites.

Perovskite solar cells are poised to be a game changer in photovoltaic technology with a current certified efficiency of 25.2%, already surpassing that for multicrystalline silicon solar cells. On the path to higher efficiencies and much needed higher stability, however, interfacial and bulk defects in the active material should be carefully engineered or passivated. Post-treatment techniques show great potential to address defect issues (e.g., by coarsening the perovskite grains or establishing an interfacial heterogeneous layer). In this article, we summarize current fundamental understanding of the major energy-loss routes in perovskite materials and devices, including bulk/interfacial defects mediated nonradiative recombination and band mismatch-induced recombination. This is followed by a survey of the important post-treatment techniques developed over the past few years to minimize energy loss in perovskite solar cells, including solvent annealing, amine halide solution dripping-induced Ostwald ripening, three-dimensional–two-dimensional interface layer from phenethylammonium iodide (PEAI) dripping, and wide bandgap interface layer engineering from n-hexyl trimethylammonium bromide washing. Finally, we provide a prospective view about further developments of post-treatment techniques.

Although halide perovskites (HaPs) are synthesized in ways that appear antithetical to those required for yielding high-quality semiconductors, the properties of the resulting materials imply, particularly for single crystals, ultralow densities of optoelectronically active defects. This article provides different views of this unusual behavior. We pose the question: Can present models of point defects in solids be used to interpret the experimental data and provide predictive power? The question arises because the measured ultralow densities refer to static defects using our present methods and models, while dynamic defect densities are ultrahigh, a result of the material being relatively soft, with a shallow electrostatic energy landscape, and with anharmonic lattice dynamics. All of these factors make the effects of dynamic defects on the materials’ optoelectronic properties minimal. We hope this article will stimulate discussions on the nontrivial question: Are HaPs, and especially the defects within them, business as usual?

Quantum computing, sensing, and communications are emerging technologies that may circumvent known limitations of their existing traditional counterparts. While the promises of these technologies are currently narrow in scope, it is possible that they will broadly impact our lives by revolutionizing the capabilities of data centers and medical diagnostics, for example. At the heart of these technologies is the use of a quantum object to contain information, called a quantum bit or qubit. Current realizations of qubits exist in a broad variety of material systems, including individual spins in semiconductors or insulators, superconducting circuits, and trapped ions. Further advancement of qubits requires significant contributions from materials science in areas of materials selection, synthesis, fabrication, simulation and characterization. Here, we discuss some of the needs and opportunities for contributions to advance the fundamental understanding of materials used in quantum information applications.

Because of their structural versatility, fast redox reactivity, high storage capacity, sustainability, and environmental friendliness, soluble organic redox molecules have emerged as materials that have potential for use in energy-storage systems. Considering these advantages, this paper reviews recent progress in implementing such materials in aqueous soluble organic redox flow batteries and organic alkali metal/air batteries. We identify and discuss major challenges associated with molecular structures, cell configurations, and electrochemical parameters. Hopefully, we provide a general guidance for the future development of soluble organic redox materials for emerging energy-storage devices used in the electricity grid.

Iron oxide nanoparticles presenting colloidal stability in water were prepared through precipitation and then surface-functionalized with varying citric acid (CA) concentrations (0.10, 0.25, 0.50, and 0.70 g/mL). CA introduced functionality and minimized agglomeration. Iron oxide nanoparticles with colloidal stability in water at physiological pH were obtained after functionalization with 0.25–0.70 g/mL CA, whereas iron oxide nanoparticles without stability in water were obtained after functionalization with 0.10 g/mL CA. An electrode for glucose detection was fabricated by self-assembling colloidal-stable γ-Fe2O3 NP–CA in water on indium tin oxide (ITO) glass, followed by a glucose oxidase (GOx) and Nafion layer. The optimal functionalization of the γ-Fe2O3 NPs was obtained at a CA concentration of 0.25 g/mL. The electrochemical properties and electrocatalytic behavior of the modified electrode designated as Nafion/GOx/γ-Fe2O3 NP–0.25 CA/ITO were then evaluated. The electrode showed high sensitivity for glucose detection of 995.57 and 5.81 µA/(mM cm2) within the linear ranges of 0.1–5.0 µM and 5.0 µM–20.0 mM, respectively. The modified electrode also demonstrated a low limit of detection, good repeatability of 2.5% (n = 10), and sufficient reproducibility of 3.2% (n = 5).