In recent years, there have been rapid advances in the synthesis of lead halide perovskite nanocrystals (NCs) for use in solar cells, light emitting diodes, lasers, and photodetectors. These compounds have a set of intriguing optical, excitonic, and charge transport properties, including outstanding photoluminescence quantum yield (PLQY) and tunable optical band gap. However, the necessary inclusion of lead, a toxic element, raises a critical concern for future commercial development. To address the toxicity issue, intense recent research effort has been devoted to developing lead‐free halide perovskite (LFHP) NCs. In this Review, we present a comprehensive overview of currently explored LFHP NCs with an emphasis on their crystal structures, synthesis, optical properties, and environmental stabilities (e.g., UV, heat, and moisture resistance). In addition, strategies for enhancing optical properties and stabilities of LFHP NCs as well as the state‐of‐the‐art applications are discussed. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high‐quality LFHP NCs for a broader range of fundamental research and practical applications.

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We have followed the time development of the microdomain structure in symmetric diblock copolymer poly(styrene-b-methyl methacrylate), P(S-b-MMA), ultrathin films via PMMA-selective solvent vapor treatment by atomic force microscopy (AFM). After preparation on a substrate preferentially attracting the PMMA block, PS forms a continuous layer at a film's free surface. With subsequent solvent vapor treatment, the film gradually shows a well-ordered hexagonally packed nanocylinders structure. It is shown that only when the film thickness is less than the 1 /2L0 (lamellar repeat spacing), and exposed to PMMA block selective solvent for an appropriate time, can the well-ordered hexagonally packed nanocylinders form. On an extended solvent vapor treatment, a mixed morphology containing nanocylinders and stripes appears, followed by the striped morphologies. When the annealing time is long enough, the film comes back to the flat surface again, however, with PMMA instead of PS dominating the free surface. Thickness confinement and solvent induced reconstruction of the film are shown to be responsible for the P(S-b-MMA) morphology and surface chemistry development.

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We have systematically studied the thin film morphologies of symmetric poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer after annealing to solvents with varying selectivity. Upon neutral solvent vapor annealing, terraced morphology is observed without any lateral structures on the surfaces. When using PS-selective solvent annealing, the film exhibits macroscopically flat with a disordered micellar structure. While PMMA-selective solvent annealing leads to the dewetting of the film with fractal-like holes, with highly ordered nanoscale depressions in the region of undewetted films. In addition, when decreasing the swelling degree of the film in the case of PMMA-selective solvent annealing, hills and valleys are observed with the coexistence of highly ordered nanoscale spheres and stripes on the surface, in contrast to the case of higher swelling degree. The differences are explained qualitatively on the basis of polymer-solvent interaction parameters of the different components.

Up to now, little effort has been made to exploit large-area high-throughput patterning by block copolymer (BCP) lithography to generate nanostructured substrates with periods well below 100 nm for surface-enhanced Raman scattering (SERS). We show that simple BCP-templated galvanic displacement reactions yield dense arrays of mushroom-shaped gold nanopillars with a period of 50 nm. The nanoporous BCP films used as templates were obtained by swelling-induced reconstruction of reverse micelle monolayers deposited on silicon wafers. Coupling of adjacent mushroom caps almost impinging on each other combined with their strong local curvature results in a high spatial density of hot spots in the narrow gaps between them. Thus, substrates characterized by high SERS efficiencies are obtained.

We have studied the surface morphology of symmetric poly(styrene)-block-poly(methyl methacrylate) diblock copolymer thin films after solvent vapor treatment selective for poly(methyl methacrylate). Highly ordered nanoscale depressions or striped morphologies are obtained by varying the solvent annealing time. The resulting nanostructured films turn out to be sensitive to the surrounding medium, that is, their morphologies and surface properties can be reversibly switchable upon exposure to different block-selective solvents.

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature-sensitive polymer ligands.S trikingly,s ignificant discrepancies in optical and catalytic properties of thermoresponsive noble-metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM), in situ using as tarlike blockc opolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises,p lasmonic absorption of PNIPAM-capped Au NPs red-shifts with increased intensity in the absence of free linear PNIPAM, whereas ag reater red-shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably,t he absence or addition of free linear PNIPAM also accounts for non-monotonic or switchable on/off catalytic performance,respectively,ofPNIPAM-capped Au NPs.