The development of green, sustainable, and economical chemical processes represents a cornerstone challenge within chemistry today. Semiconductor heterogeneous photocatalysis is currently utilized within a wide variety of societally impactful processes, spanning reactions such as hydrogen production and CO2 conversion, to the organic transformation of raw materials for value-added chemicals. Metal halide perovskites (MHPs) have recently emerged as a new promising class of cheap and easy to make photocatalytic semiconductors, though their unstable ionically bound crystal structure has thus far restricted widespread application. In this Review, we examine the issues hampering MHP-based photocatalysis and highlight the general approaches being taken to achieve promising and stable photocatalytic reaction environments. Specifically, we outline the adoption of (1) halogen acid solutions (i.e., HX; X = I or Br) for hydrogen evolution reactions, (2) relatively low-polarity solvents for CO2 photoreduction and organic transformations, and (3) the encapsulation of perovskites for CO2 reduction and water splitting. Further, we detail the measures being taken to arrive at intrinsically stable photocatalytic materials, removing the need for atypical environments. With each technology offering unique sets of benefits and challenges, we conclude by outlining potentially promising opportunities and directions for metal halide perovskite-based photocatalysis research moving forward.

includes self-assembled fullerene crystals design from zero-to-higher dimensions, mesoporous fullerene crystals and their conversion into graphitic mesoporous carbons, high surface area nanoporous carbon material design from agro-waste for electrochemical supercapacitors and VOC adsorption. Somobrata AcharyaSomobrata Acharya received his Ph.D. degree from Jadavpur University, India. He is currently Associate Professor in the Centre for Advanced Materials (CAM), Indian Association for the Cultivation of Science (IACS), India. He is carrying out research in interdisciplinary areas probing structure-property relationship and possible applications of semiconductor nanomaterials in the areas of energy generation and consumption. His research area includes heterostructures, 2D nanostructures, superlattices, supramolecular assemblies and their suitable applications. Katsuhiko ArigaKatsuhiko Ariga received his Ph.D. degree from Tokyo Institute of Technology. He is currently the Director of Supermolecules Group and Principal Investigator of World Premier International (WPI) Research Centre for Materials Nanoarchitectonics (MANA), the National Institute for Materials Science (NIMS). His research is oriented to supramolecular chemistry, surface science, and functional nanomaterials (Langmuir-Blodgett film, layer-by-layer assembly, self-organized materials, sensing and drug delivery, molecular recognition, mesoporous material, etc. and he is now trying to combine them into a unified field. AbstractDesigning nanoscale components and units into functional defined systems and materials has recently received attention as a nanoarchitectonics approach. In particular, exploration of nanoarchitectonics in two-dimensions (2D) has made great progress these days. Basically, 2D nanomaterials are a center of interest owing to the large surface areas suitable for a variety of surface active applications. The increasing demands for alternative energy generation have significantly promoted the rational design and fabrication of a variety of 2D nanomaterials since the discovery of graphene. In 2D nanomaterials, the charge carriers are confined along the thickness while being allowed to move along the plane. Owing to the large planar area, 2D nanomaterials are highly sensitive to external stimuli, a characteristic suitable for a variety of surface active applications including electrochemistry. Because of the unique

All-inorganic perovskite nanocrystals are emergent alternative of organolead halide perovskites. Cesium antimony halide (Cs3Sb2X9, X = Cl, Br, I) all-inorganic perovskites nanocrystals possessing analogous electronic configuration to the organolead halide perovskites are promising materials for optoelectronic applications. We report on a colloidal route to synthesis uniform Cs3Sb2Cl9 perovskite nanowires with lengths up to several microns. We have synthesized aspect ratio controlled nanorods with the same ∼20 nm diameter of nanowires by tuning the precursors and ligands in the reaction. The crystallinity of the nanocrystals is significantly altered from the pristine bulk trigonal and orthorhombic phases owing to the one-dimensional shape of the nanocrystals. Rietveld refinement carefully separates out orthorhombic phase from the trigonal phase revealing a coexistence of both the phases in a minor and major ratio in the nanocrystals. The functionality in the form of fast photodetector demonstrates Cs3Sb2Cl9 nanocrystals as promising materials for optoelectronic applications.

Semiconductor-based light detection finds widespread application in everyday devices. Since the fabrication of commercial photodetectors requires complex and capital-intensive equipment, a search for semiconductors with low-cost processing is essential. To this end, hybrid organic–inorganic metal halide perovskites (MHPs) have gained interest due to their facile processing, in combination with their outstanding properties, such as efficient light absorption and high carrier mobility. Recently, all-inorganic CsPbBr3 has emerged as a promising candidate for photodetection due to its favorable intermediate bandgap and superior photostability, thermal stability, and moisture stability. Different synthesis strategies have been adopted to obtain highly crystalline CsPbBr3 perovskites with a large variety in morphology and dimension, each allowing for a specific photodetector application, e.g., cameras for hand-held devices, large-area flat panel detectors, and flexible light sensors. This Review provides a comprehensive overview and evaluation of the state-of-the-art preparation and photodetector integration of CsPbBr3 single crystals, microcrystals, nanowires, thin films, and nanocrystals.

Organometal halide perovskites in the form of nanocrystals (NCs) have attracted enormous attention due to their unique optoelectronic and photoluminescence (PL) properties. Here, we examine the phase composition and the temperature dependence of emission line width broadening in formamidinium lead bromide (FAPbBr) perovskite nanocrystals (NCs) for light-emitting applications and identify different charge-carrier scattering mechanisms. Our results show most of the emission is from the orthorhombic phase. The PL line width broadening at high temperature is dominated by the Fröhlich interaction between the free charge carriers and the optical phonons. At low temperatures, the peak of the PL spectrum exhibits a continuous red shift indicating an increase of excitons contribution at lower temperatures, and concurrently the line width also narrows down due to the inhibition of the optical phonons. From the temperature-dependent measurements, the coupling strength of both the charge phonon interaction and the exciton phonon interaction have been determined. The obtained results indicate that the charge phonon coupling strengths are higher compared to the exciton phonon coupling.

Lead halide perovskite materials have shown strong promise in energy harvesting and generation over the past five years. However, their poor ambient stability and lead toxicity issues hinder optoelectronic applications. In the quest for alternatives, metal halide perovskites with lower toxicity and more stable metals have recently emerged. The divalent Pb2+ could be replaced with isoelectronic Sn2+, but Sn2+ tends to oxidize rapidly in presence of air to Sn4+, forming a defect in the structure. However, Sn2+‐based perovskites have been stabilized in 2D structures. Recently Sn4+ based halide perovskites nanocrystals with have been reported with poor luminescence. The replacement of Pb2+ with isoelectronic trivalent elements (Sb3+, Bi3+) results in A3B2X9 type defect‐order perovskite structure, which shows promises for optoelectronic applications. The perovskite nanocrystals of Sb, Bi have been reported in the form of dimers and layered structures. In addition to these, double perovskites, where two divalent Pb2+ are replaced with a monovalent and a trivalent cation have been reported very recently. In this Focus Review, we give a brief summary of different non‐lead perovskite nanocrystals starting from synthesis, characterization, stability, properties to applications, along with potential future directions.

We represent a facile colloidal synthesis of halide tunable, structurally distorted Cs3Bi2Br9(1–x)I9x (0 ≤ x ≤ 1) nanocrystals. The detail structural characterization establishes phase purity of the as-synthesized perovskite nanocrystals. The lattice parameters follow a linear trend in agreement with Vegard’s law, confirming the homogeneous gradient alloying of the nanocrystals through entropic halide mixing up to a certain degree of alloying. Systematic Raman analysis also proves the complete homogeneous solid solution formation across the entire compositional window. Simultaneous optical and cyclic voltammetry measurements corroborate a band gap variation in the range of 1.97–2.72 eV, consistent with the pure end (x = 0 and 1) compounds. A stable photodetector was fabricated with pristine and alloyed nanocrystals where the best performance was achieved for Cs3Bi2I9. The functionality in the form of a fast photodetector suggests that these Cs3Bi2Br9(1–x)I9x nanocrystals are prospective optoelectronic materials. The present study provides an evidence of tunable optical window for mixed halide all-inorganic bismuth halide perovskites toward photodetector applications.

All inorganic mixed-halide perovskite, CsPb­(Br x I1–x )3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb­(Br x I1–x )3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.