Recent Advances in Synthesis, Properties, and Applications of Metal Halide Perovskite Nanocrystals/Polymer Nanocomposites

Precise Control Light Emission of PVDF-CH3NH3PbBr3-xClx Nanocrystalline Films Using a Cl-(CH3OH)n System

Methylammonium lead halide perovskites with highly efficient pure-color or white-light generation have gained increasing scientific interest and promote the development of a great commercial opportunity in displays, lighting, and other applications. However, the poor stabilities, lead toxicity, and unfriendly solvents and ligands in the growth process severely restrict their commercial application. Here, we proposed a green method for preparing uniform and stable polymer-encapsulated photoluminescence (PL) tunable CH3NH3PbBr3-xClx NC thin films at room temperature. Utilizing the swelling effect between alcohol compounds and organic polymers and the ionization of NaCl in methanol solution, the anion exchange process can be achieved rapidly within 7 min. Moreover, the PL wavelengths of the CH3NH3PbBr3-xClx NCs films were precisely tuned with steps as fine as 2 nm. Experimental results showed that NaCl dissolved in methanol solution can form Cl-(CH3OH)n, which brings ionized Cl into the polymer-encapsulated CH3NH3PbBr3 NCs film for CH3NH3PbBr3-xClx NCs film growth. Based on the swelling and anion exchange dynamics, a modified NaCl-CH3OH-MABr solution system was developed to trigger CH3NH3PbBr3-xClx NCs film PL emission tuning from 528 to 463 nm with several-fold intensity enhancement. The realization of precisely controlled photoluminescence from the perovskite nanocrystal film would have wide applications in the optical and imaging fields.

Highly Stable Cesium Molybdenum Chloride Perovskite Nanocrystals for Photothermal Semihydrogenation Applications

Metal halide perovskite materials with excellent carrier transport properties have been regarded as a new class of catalysts with great application potential. However, their development is hampered by their instability in polar solvents and high temperatures. Herein, we report a solution-processed Cs2MoCl6 perovskite nanocrystals (NCs) capped with the Mo6+, showing high thermostability in polar solvents. Furthermore, the Pd single atoms (PdSA) can be anchored on the surface of Cs2MoCl6 NCs through the unique coordination structure of Pd-Cl sites, which exhibit excellent semihydrogenation of different alkyne derivatives with high selectivity at full conversion at room temperature. Moreover, the activity could be improved greatly under Xe lamp irradiation. Detailed experimental characterization and DFT calculations indicate the improved activity under light illumination is due to the synergistic effect of photo-to-heat conversion and photoinduced electron transfer from Cs2MoCl6 to PdSA, which facilitates the activation of the C≡C group. This work not only provides a new catalyst for high selective semihydrogenation of alkyne derivatives but also opens a new avenue for metal halides as photothermal catalysts.

Conductivity-mediated in situ electrochemical reconstruction of CuOx for nitrate reduction to ammonia

The electrocatalytic nitrate reduction reaction (NO3RR) is an ideal NH3 synthesis route with ease of operation, high energy efficiency, and low environmental detriment. Electrocatalytic cathodes play a dominant role in the NO3RR. Herein, we constructed a carbon fiber paper-supported CuOx nanoarray catalyst (CP/CuOx) by an in situ electrochemical reconstruction method for NO3--to-NH3 conversion. A series of characterization techniques, such as X-ray diffraction (XRD) and in situ Raman spectroscopy, unveil that CP/CuOx is a polycrystalline-faceted composite copper nanocatalyst with a valence composition containing Cu0, Cu+ and Cu2+. CP/CuOx shows more efficient NO3--to-NH3 conversion than CP/Cu and CP/Cu2O, which indicates that the coexistence of various Cu valence states could play a dominant role. CP/CuOx with a suitable Cu2+ content obtained by adjusting the conductivity during the in situ electrochemical reconstruction process exhibited more than 90% faradaic efficiencies for the NO3RR in a broad range of -0.3 to -1.0 V vs. RHE, 28.65 mg cm-2 h-1 peak ammonia yield, and stable NO3RR efficiencies for ten cycles. These findings suggest that CP/CuOx with suitable copper valence states obtained by fine-tuning the conductivity of the electrochemical reconstruction may provide a competitive cathode catalyst for achieving excellent activity and selectivity of NO3--to-NH3 conversion.

Room temperature synthesis of nanocomposite thin films with embedded Cs2AgIn0.9Bi0.1Cl6 lead-free double perovskite nanocrystals with long-term water stability, wide range pH tolerance, and high quantum yield

The synthesis of Cs2AgIn0.9Bi0.1Cl6 nanocrystals was achieved at room temperature under ambient conditions using the ligand-assisted reprecipitation (LARP) method. The synthesized NCs exhibit bright orange emission when excited at 375 nm and have broad photoluminescence (PL) emission spectra with a maximum of 630 nm. A photoluminescence quantum yield (PLQY) of 36% was observed in these NCs without any polymer coatings. Polystyrene (PS), and poly (methyl methacrylate) (PMMA) were used to enhance the water stability and PLQY values up to 64%. Nanocomposite thin films with these polymer encapsulations exhibit good thermal stability up to at least 353 K and high quantum yields. PMMA-coated NCs showed long-term water stability for at least 4 months. The composites remain photostable when in contact with water for at least 120 min under continuous 365 nm UV illumination at 1 mW cm-2. Due to their excellent optical properties, aqueous stability, and wide range pH tolerance, these nanocomposite thin films could be employed for a variety of biological applications.

Hot-Injection Synthesis of Cesium Lead Halide Perovskite Nanowires with Tunable Optical Properties

Metal halide perovskite semiconductors have emerged as promising materials for various optoelectronic applications due to their unique crystal structure and outstanding properties. Among different forms, perovskite nanowires (NWs) offer distinct advantages, including a high aspect ratio, superior crystallinity, excellent light absorption, and carrier transport properties, as well as unique anisotropic luminescence properties. Understanding the formation mechanism and structure-property relationship of perovskite NWs is crucial for exploring their potential in optoelectronic devices. In this study, we successfully synthesized all-inorganic halide perovskite NWs with high aspect ratios and an orthorhombic crystal phase using the hot-injection method with controlled reaction conditions and surface ligands. These NWs exhibit excellent optical and electrical properties. Moreover, precise control over the halogen composition through a simple anion exchange process enables the tuning of the bandgap, leading to fluorescence emission, covering a wide range of colors across the visible spectrum. Consequently, these perovskite NWs hold great potential for efficient energy conversion and catalytic applications in photoelectrocatalysis.

Investigating the effect of Zn doping and temperature on the photoluminescence behaviour of CuLaSe2 quantum dots

In this study, CuLaSe2 and ZnCuLaSe2 quantum dots (QDs) with a mean size of ~4 nm were synthesized and characterized, and their temperature-dependent photoluminescence (PL) properties were studied in the temperature range from 90 to 300 K for the first time. The results show that the obtained QDs were spherical and revealed excitonic band gaps. The PL intensity for both types of materials decreased when increasing the temperature to 300 K, which was attributed to the nonradiative relaxation and thermal escape mechanisms. As the temperature was increased, the PL linewidths broadened, and PL peak energies were red shifted for both types of QDs due to the exciton-phonon coupling and lattice deformation potential mechanisms. In addition, we found that as the temperature was decreased, the PL spectrum of ZnCuLaSe2 QDs contained two extra components, which could be attributed to the shallow defect sites (low energy peak) and the crystal phase transition process (high energy peak). The spectrum of CuLaSe2 QDs contained one extra component, which could be attributed to the crystal phase transition process.

Colloidal Synthesis of Hollow Double Perovskite Nanocrystals and Their Applications in X-ray Imaging

Rare earth-based halide double perovskites are regarded as an emerging class of X-ray scintillation materials. However, the majority of related scintillator applications are still focused on single crystal and powder systems; the application of nanocrystal (NC) scintillators is rarely reported. Here, we present the synthesis of high-purity Cs2NaTbCl6 NCs by an improved hot-injection method. Interestingly, hollow Cs2NaTbCl6 NCs are observed, the monitoring of the growth process indicates that micrometer-sized NaCl is the initial product, and then the NaCl would convert into Cs2NaTbCl6 NCs through the diffusion of Cs+ and Tb3+ into NaCl lattice, and the faster outward diffusion of Na+ results in the formation of hollow NCs. The double perovskite NCs exhibit green light emission, and the photoluminescence intensity can be significantly enhanced through Ce3+ doping. In particular, the Cs2NaTbCl6:5%Ce3+ scintillator exhibits a linear response and a low detection limit of 79.09 nGy/s when exposed to X-rays. Furthermore, a flexible scintillator film for X-ray imaging is prepared by mixing NCs with polymer, showing a high spatial resolution imaging capability of 10 lp/mm. This work provides a new strategy for hollow perovskite NCs and may shed light on the synthesis of related hollow NCs and their applications in X-ray detection.

Multiscale Supercrystal Meta-atoms

Meta-atoms are the building blocks of metamaterials, which are employed to control both generation and propagation of light as well as provide novel functionalities of localization and directivity of electromagnetic radiation. In many cases, simple dielectric or metallic resonators are employed as meta-atoms to create different types of electromagnetic metamaterials. Here, we fabricate and study supercrystal meta-atoms composed of coupled perovskite quantum dots. We reveal that these multiscale structures exhibit specific emission properties, such as spectrum splitting and polaritonic effects. We believe that such multiscale supercrystal meta-atoms will provide novel functionalities in the design of many novel types of active metamaterials and metasurfaces.

Nanocrystals as performance-boosting materials for solar cells

Nanocrystals (NCs) have been widely studied owing to their distinctive properties and promising application in new-generation photoelectric devices. In photovoltaic devices, semiconductor NCs can act as efficient light harvesters for high-performance solar cells. Besides light absorption, NCs have shown great significance as functional layers for charge (hole and electron) transport and interface modification to improve the power conversion efficiency and stability of solar cells. NC-based functional layers can boost hole/electron transport ability, adjust energy level alignment between a light absorbing layer and charge transport layer, broaden the absorption range of an active layer, enhance intrinsic stability, and reduce fabrication cost. In this review, recent advances in NCs as a hole transport layer, electron transport layer, and interfacial layer are discussed. Additionally, NC additives to improve the performance of solar cells are demonstrated. Finally, a summary and future prospects of NC-based functional materials in solar cells are presented, addressing their limitations and suggesting potential solutions.

Polymeric Metal Halides with Bright Luminescence and Versatile Processability

Most of current metal halide materials, including all inorganic and organic-inorganic hybrids, are crystalline materials with poor workability and plasticity that limit their application scope. Here, we develop a novel class of materials termed polymeric metal halides (PMHs) through introducing polycations into antimony-based metal halide materials as A-site cations. A series of PMHs with orange-yellow broadband emission and large Stokes shift originating from inorganic self-trapped excitons are successfully prepared, which meanwhile exhibit the excellent processability and formability of polymers. The versatility of these PMHs is manifested as the broad choices of polycations, the ready extension to manganese- and copper-based halides, and the tolerance to molar ratios between polycations and metal halides in the formation of PMHs. The merger of polymer chemistry and inorganic chemistry thus provides a novel generic platform for the development of metal halide functional materials.

An all-inorganic lead-free metal halide double perovskite for the highly selective detection of norfloxacin in aqueous solution

Lead-based perovskites are highly susceptible to environmental influences, and their application in analytical chemistry, especially in aqueous solution, has been reported rarely. All-inorganic lead-free metal halide perovskites have been considered as a substitute for lead-based perovskites. Herein, a Cs2RbTbCl6 perovskite microcrystal (PMCs), which emits strong yellow-green fluorescence with a maximum emission wavelength at 547 nm, was for the first time  synthesized and characterized. The Cs2RbTbCl6 PMCs could be well dispersed in N,N-dimethylacetamide (DMF), and its fluorescence could be significantly enhanced by the addition of norfloxacin (NOR) in the aqueous solution. We found that the Cs2RbTbCl6 PMCs can be used as fluorescent probes (excitation, 365 nm; emission, 547 nm) to selectively detect NOR in a concentration range from 10.0 to 200.0 μM with the limit of detection (LOD) being 0.04 μM. The Cs2RbTbCl6 PMCs could also be adsorbed on filter paper to fabricate as a fluorescent test paper for visual detection of NOR under 365-nm ultraviolet (UV) lamp irradiation. The proposed method has the potential to establish a new analytical method to visualize the detection of NOR in aqueous environments and also promotes the application of all-inorganic lead-free perovskites for analytical detection in aqueous environments.

Scintillation Properties of CsPbBr3 Nanocrystals Prepared by Ligand-Assisted Reprecipitation and Dual Effect of Polyacrylate Encapsulation toward Scalable Ultrafast Radiation Detectors

Lead halide perovskite nanocrystals (LHP-NCs) embedded in polymeric hosts are gaining attention as scalable and low-cost scintillation detectors for technologically relevant applications. Despite rapid progress, little is currently known about the scintillation properties and stability of LHP-NCs prepared by the ligand assisted reprecipitation (LARP) method, which allows mass scalability at room temperature unmatched by any other type of nanostructure, and the implications of incorporating LHP-NCs into polyacrylate hosts are still largely debated. Here, we show that LARP-synthesized CsPbBr3 NCs are comparable to particles from hot-injection routes and unravel the dual effect of polyacrylate incorporation, where the partial degradation of LHP-NCs luminescence is counterbalanced by the passivation of electron-poor defects by the host acrylic groups. Experiments on NCs with tailored surface defects show that the balance between such antithetical effects of polymer embedding is determined by the surface defect density of the NCs and provide guidelines for further material optimization.

Highly Sensitive H2S Gas Sensor Based on a Lead-Free CsCu2I3 Perovskite Film at Room Temperature

Recently, there have been reports of lead halide perovskite-based sensors demonstrating their potential for gas sensing applications. However, the toxicity of lead and the instability of lead-based perovskites have limited their applications. This study addressed this issue by developing a H2S gas sensor based on a lead-free CsCu2I3 film prepared using a one-step CVD method. The sensor demonstrated excellent sensing properties, including a high response and selectivity toward H2S, even at low concentrations (0.2 ppm) at room temperature. Furthermore, a reasonable sensing mechanism was proposed. It is suggested that the sensing mechanism sheds light on the role of defects in perovskite materials, the impact of H2S as an electron donor, and the occurrence of reversible chemical reactions. These findings suggest that lead-free CsCu2I3 has great potential in the field of H2S gas sensing.

Customizable Scintillator of Cs3 Cu2 I5 :2% In+ @Paper for Large-Area X-Ray Imaging

High-resolution X-ray imaging is increasingly required for medical diagnosis and large-area detection. However, the issues of scattering and optical crosstalk are limiting the spatial resolution of the indirect X-ray imaging. In this study, a feasible and efficient strategy is proposed to in situ synthesize flexible Cs3 Cu2 I5 :2%In+ @paper as a superior scintillator film, which can be scaled up to an ultra-large area of 4800 cm2 . The as-obtained Cs3 Cu2 I5 :2%In+ @paper performs a fascinating photoluminescence quantum efficiency up to 88.14%, a steady state light yield of 70169 photons/MeV, and spatial resolution of 15 lp mm-1 . Moreover, the suppressed physical scattering and optical crosstalk of the corresponding film are demonstrated. Accordingly, this work explores a feasible fabrication of customizable scintillation films with large area for high-resolution X-ray detection.

Bulk CsPbClxBr3-x (1 ≤ x ≤ 3) perovskite nanocrystals/polystyrene nanocomposites with controlled Rayleigh scattering for light guide plate

Perovskite nanocrystals (PNCs)/polymer nanocomposites can combine the advantages of each other, but extremely few works can achieve the fabrication of PNCs/polymer nanocomposites by bulk polymerization. We originally adopt a two-type ligand strategy to fabricate bulk PNCs/polystyrene (PS) nanocomposites, including a new type of synthetic polymerizable ligand. The CsPbCl3 PNCs/PS nanocomposites show extremely high transparency even the doping content up to 5 wt%. The high transparency can be ascribed to the Rayleigh scattering as the PNCs distribute uniformly without obvious aggregation. Based on this behavior, we first exploit the potential of PNCs to serve as scatters inside light guided plate (LGP), whose surface illuminance and uniformity can be improved, and this new kind of LGP is compatible with the advanced liquid crystal display technology. Thanks to the facile composition adjustment of CsPbClxBr3-x (1 ≤ x ≤ 3) PNCs, the Rayleigh scattering behavior can also be adjusted so as to the performance of LGP. The best-performing 5.0-inch LGP based on CsPbCl2.5Br0.5 PNCs/PS nanocomposites shows 20.5 times higher illuminance and 1.8 times higher uniformity in display than the control. The LGP based on PNCs/PS nanocomposite exhibits an enormous potential in commercialization no matter based on itself or combined with the LGP-related technology.

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn²⁺ into OIHP is expected to introduce a ⁴T₁-⁶A₁-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn²⁺ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (¹O₂), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)₂PbBr₄ (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn²⁺ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based ¹O₂ generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from β-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb²⁺ exciton to alloyed Mn²⁺ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

Flexible All-Inorganic Perovskite Photodetector with a Combined Soft-Hard Layer Produced by Ligand Cross-Linking

Although perovskite nanocrystals have attracted considerable interests as emerging semiconductors in optoelectronic devices, design and fabrication of a deformable structure with high stability and flexibility while meeting the charge transport requirements remain a huge challenge. Herein, a combined soft-hard strategy is demonstrated to fabricate intrinsically flexible all-inorganic perovskite layers for photodetection via ligand cross-linking. Perfluorodecyltrichlorosilane (FDTS) is employed as the capping ligand and passivating agent bound to the CsPbBr₃ surface via Pb-F and Br-F interactions. The SiCl head groups of FDTS are hydrolyzed to produce SiOH groups which subsequently condense to form the SiOSi network. The CsPbBr₃ @FDTS nanocrystals (NCs) are monodispersed cubes with an average particle size of 13.03 nm and exhibit excellent optical stability. Furthermore, the residual hydroxyl groups on the surface of the CsPbBr₃ @FDTS render the NCs tightly packed and cross-linked to each other to form a dense and elastic CsPbBr₃ @FDTS film with soft and hard components. The photodetector based on the flexible CsPbBr₃ @FDTS film exhibits outstanding mechanical flexibility and robust stability after 5000 bending cycles.

Water-stable, biocompatible, and highly luminescent perovskite nanocrystals-embedded fiber-based paper for anti-counterfeiting applications

In this study, we present a promising and facile approach toward the fabrication of non-toxic, water-stable, and eco-friendly luminescent fiber paper composed of polycaprolactone (PCL) polymer and CsPbBr₃@SiO₂ core-shell perovskite nanocrystals. PCL-perovskite fiber paper was fabricated using a conventional electrospinning process. Transmission electron microscopy (TEM) clearly revealed incorporation of CsPbBr₃@SiO₂ nanocrystals in the fibers, while scanning electron microscopy (SEM) demonstrated that incorporation of CsPbBr₃@SiO₂ nanocrystals did not affect the surface and diameter of the PCL-perovskite fibers. In addition, thermogravimetric analysis (TGA) and contact angle measurements have demonstrated that the PCL-perovskite fibers exhibit excellent thermal and water stability. The fabricated PCL-perovskite fiber paper exhibited a bright green emission centered at 520 nm upon excitation by ultra-violet (UV) light (374 nm). We have demonstrated that fluorescent PCL-perovskite fiber paper is a promising candidate for anti-counterfeiting applications because various patterns can be printed on the paper, which only become visible after exposure to UV light at 365 nm. Cell proliferation tests revealed that the PCL-perovskite fibers are cytocompatibility. Consequently, they may be suitable for biocompatible anti-counterfeiting. The present study reveals that PCL-perovskite fibers may pave way toward next generation biomedical probe and anti-counterfeiting applications.

Continuous manufacturing of highly stable lead halide perovskite nanocrystals via a dual-reactor strategy

Lead halide perovskite nanocrystals possess incredible potential as next generation emitters due to their stellar set of optoelectronic properties. Unfortunately, their instability towards many ambient conditions and reliance on batch processing hinder their widespread utilities. Herein, we address both challenges by continuously synthesizing highly stable perovskite nanocrystals via integrating star-like block copolymer nanoreactors into a house-built flow reactor. Perovskite nanocrystals manufactured in this strategy display significantly enhanced colloidal, UV, and thermal stabilities over those synthesized with conventional ligands. Such scaling up of highly stable perovskite nanocrystals represents an important step towards their eventual use in many practical applications in optoelectronic materials and devices.

Supramolecular Framework Constructed by Dendritic Nanopolymer for Stable Flexible Perovskite Resistive Random-Access Memory

The 3D supramolecular framework (3D-SF) is constructed in this work through the hydrogen bond assisted self-assembly of spherical dendritic nanopolymer to regulate the flexibility, stability, and resistive switching (RS) performance of perovskite resistive random-access memory (RRAM). Herein, the 3D-SF network acts as the perovskite crystallization template to regulate the perovskite crystallization process due to its coordination interaction of functional groups with the perovskite grains, presenting the uniform, pinhole-free, and compact perovskite morphology for stable flexible RRAM. The 3D-SF network in situ stays at the perovskite intergranular boundaries to crosslink the perovskite grains. The RS performance of 3D-SF-modified perovskite RRAM device is evidently improved to the ON/OFF ratio of 10⁵ , the cycle number of 500 times, and the data retention time of 10⁴ s. The 50-days exposure of unencapsulated RRAM device at ambient environment still makes the ON/OFF ratio to be kept at ≈10⁴ , indicating the potential of long-term stable multilevel storage in the high-density data storage. The bending action under different radius also does not change the RS performance due to the excellent bending-resistant ability of 3D-SF-modified perovskite film. This work explores a novel polymer additive strategy to construct the 3D supramolecular framework for stable flexible perovskite optoelectronic devices.

FAPbBr3 Perovskite Nanocrystals Embedded in Poly(L-lactic acid) Nanofibrous Membranes for Enhanced Air and Water Stability

Formamidinium lead bromide (FAPbBr₃) nanocrystals have emerged as a powerful platform for optoelectronic applications due to their pure green photoluminescence (PL). However, their low colloidal stability under storage and operation reduces the potential use of FAPbBr₃ perovskite nanocrystals (PeNCs) in various applications. In this study, we prepared the poly(L-lactic acid) (PLLA) nanofibrous membrane embedded with FAPbBr₃ perovskite nanocrystals by electrospinning the perovskite and PLLA precursor solution. This is a simple and low-cost technique for the direct confinement of nano-sized functional materials in the continuous polymer nanofibres. PLLA as a polymer matrix provided a high surface framework to fully encapsulate the perovskite NCs. In addition, we found that FAPbBr₃ PeNCs crystallize spontaneously inside the PLLA nanofibre. The resultant PLLA-FAPbBr₃ nanofibrous membranes were stable and remained in the water for about 45 days without any evident decomposition. The results of this research support the idea of new possibilities for the production of air-stable FAPbBr₃ PeNCs by forming a composite with PLLA polymer. The authors believe this study is a new milestone in the development of highly stable metal halide perovskite-based nanofibres, which allow for potential use in lasers, waveguides, and flexible energy harvesters.

Ultra-stable CsPbBr3@PbBrOH nanorods for fluorescence labeling application based on methylimidazole-assisted synthesis

The extension application of perovskites in aqueous media such as bioassays requires the development of a water-stable perovskite with a simple preparation process and low cost. However, the degradation of perovskites in aqueous solution is still a thorny problem. Here, we develop a methylimidazole-assisted two-step synthesis protocol to prepare CsPbBr₃@PbBrOH nanorods with superior water stability and remarkable optical properties at room temperature. The synergy of 2-methylimidazole (2-MIM), an N-donor ligand, with water can not only facilitate CsPbBr₃ formation and suppress CsPb₂Br₅ or Cs₄PbBr₆ formation, but also promote the formation of a PbBrOH shell capping CsPbBr₃. 2-MIM is ionized into 2-MIM^- in DMF and 2-MIM⁺ in water. They passivated the surface defects and changed the crystallization environment, leading to water-stable CsPbBr₃@PbBrOH. The obtained CsPbBr₃@PbBrOH nanorods can still maintain 91% PL intensity after being stored in water for more than 2 months. Furthermore, the CsPbBr₃@PbBrOH nanorods show excellent stability in polar solvents, water, and phosphate buffer solution in a wide pH range, as well as better thermal and irradiation stability. In addition, the CsPbBr₃@PbBrOH nanorods are further functionalized with polydopamine (PDA) for biomolecular immobilization and immunoassay studies. The resulting assay shows a detection limit of 0.003 ng mL^-1 for IgG detection, illustrating important progress towards expanding fluorescence labeling application of perovskite nanomaterials for immunoassays.

Self-Charging Piezo-Supercapacitor: One-Step Mechanical Energy Conversion and Storage

With the contemplations of ecological and environmental issues related to energy harvesting, piezoelectric nanogenerators (PNGs) may be an accessible, sustainable, and abundant elective wellspring of energy in the future. The PNGs' power output, however, is dependent on the mechanical energy input, which will be intermittent if the mechanical energy is not continuous. This is a fatal flaw for electronics that need continuous power. Here, a self-charging flexible supercapacitor (PSCFS) is successfully realized that can harvest sporadic mechanical energy, convert it to electrical energy, and simultaneously store power. Initially, chemically processed multimetallic oxide, namely, copper cobalt nickel oxide (CuCoNiO₄) is amalgamated within the poly(vinylidene fluoride) (PVDF) framework in different wt % to realize high-performance PNGs. The combination of CuCoNiO₄ as filler creates a notable electroactive phase inside the PVDF matrix, and the composite realized by combining 1 wt % CuCoNiO₄ with PVDF, coined as PNCU 1, exhibits the highest electroactive phase (>86%). Under periodic hammering (∼100 kPa), PNGs fabricated with this optimized composite film deliver an instantaneous voltage of ∼67.9 V and a current of ∼4.15 μA. Furthermore, PNG 1 is ingeniously integrated into a supercapacitor to construct PSCFS, using PNCU 1 as a separator and CuCoNiO₄ nanowires on carbon cloth (CC) as the positive and negative electrodes. The self-charging behavior of the rectifier-free storage device was established under bending deformation. The PSCFS device exhibits ∼845 mV from its initial open-circuit potential ∼35 mV in ∼220 s under periodic bending of 180° at a frequency of 1 Hz. The PSCFS can power up various portable electronic appliances such as calculators, watches, and LEDs. This work offers a high-performance, self-powered device that can be used to replace bulky batteries in everyday electronic devices by harnessing mechanical energy, converting mechanical energy from its environment into electrical energy.

Synergy of Block Copolymers and Perovskites: Template Growth through Self-Assembly

Block copolymers (BCPs) have been widely used as templates to prepare nanostructures over the past few decades. Ordered nanostructures can be formed after microphase segregation of BCPs. In this context, the newly emerging BCP-templated perovskites, in which the perovskite crystal growth has been confined within a self-assembled BCP nanostructure due to the interaction between the polymer block and the cation of the perovskite, have shown profound optical performance and environmental stability. Considering the promising performance of BCP-templated perovskites, this Perspective comprehensively reviews recent works in which BCPs are used as templates with three-dimensional perovskites and perovskite quantum dots, and their performance and stability are thoroughly discussed. Lastly, their potential applications in optoelectronics and biology are discussed.

Weakening Ligand-Liquid Affinity to Suppress the Desorption of Surface-Passivated Ligands from Perovskite Nanocrystals

The interfacial migration of surface-bound ligands highly affects the colloidal stability and optical quality of semiconductor nanocrystals, of which the underlying mechanism is not fully understood. Herein, colloidal CsPbBr₃ perovskite nanocrystals (PNCs) with fragile dynamic equilibrium of ligands are taken as the examples to reveal the important role of balancing ligand-solid/solvent affinity in suppressing the desorption of ligands. As a micellar surfactant, glycyrrhizic acid (GA) with bulky hydrophobic and hydrophilic groups exhibits a relatively smaller diffusion coefficient (∼440 μm²/s in methanol) and weaker ligand-liquid affinity than that of conventional alkyl amine and carboxy ligands. Consequently, hydrophilic GA-passivated PNCs (PNCs-GA) show excellent colloidal stability in various polar solvents with dielectric constant ranging from 2.2 to 32.6 and efficient photoluminescence with a quantum yield of 85.3%. Due to the suppressed desorption of GA, the morphological and optical properties of PNCs-GA are well maintained after five rounds purification and two months long-term storage. At last, hydrophilic PNCs-GA are successfully patterned through inkjet- and screen-printing technology. These findings offer deep insights into the interfacial chemistry of colloidal NCs and provide a universal strategy for preparing high-quality hydrophilic PNCs.

Go beyond the limit: Rationally designed mixed-dimensional perovskite/semiconductor heterostructures and their applications

Halide perovskite heterojunctions rationally integrate the chemical and physical properties of multi-dimensional perovskites and judiciously chosen semiconductor materials, offering the promise of going beyond the limit of a single component. This emerging platform of materials innovation offers fresh opportunities to tune material properties, discover interesting phenomena, and enable novel applications. In this review, we first discuss the fundamentals of forming heterojunctions with perovskites and a wide range of semiconductors, and then we give an overview of the research progress of halide perovskite heterojunctions in terms of their optical, electrical, and mechanical properties, focusing on how the heterojunction tunes the energy band structure, electrical transport, and charge recombination behaviors. We further outline the progress of perovskite-based heterojunctions in optoelectronics. Finally, the challenges and future research directions for perovskite/semiconductor heterojunctions are discussed.

Stereolithography of Semiconductor Silver and Acrylic-Based Nanocomposites

Polymer nanocomposites (PNCs) attract the attention of researchers and industry because of their potential properties in widespread fields. Specifically, electrically conductive and semiconductor PNCs are gaining interest as promising materials for biomedical, optoelectronic and sensing applications, among others. Here, metallic nanoparticles (NPs) are extensively used as nanoadditives to increase the electrical conductivity of mere acrylic resin. As the in situ formation of metallic NPs within the acrylic matrix is hindered by the solubility of the NP precursors, we propose a method to increase the density of Ag NPs by using different intermediate solvents, allowing preparation of Ag/acrylic resin nanocomposites with improved electrical behaviour. We fabricated 3D structures using stereolithography (SLA) by dissolving different quantities of metal precursor (AgClO₄) in methanol and in N,N-dimethylformamide (DMF) and adding these solutions to the acrylic resin. The high density of Ag NPs obtained notably increases the electrical conductivity of the nanocomposites, reaching the semiconductor regime. We analysed the effect of the auxiliary solvents during the printing process and the implications on the mechanical properties and the degree of cure of the fabricated nanocomposites. The good quality of the materials prepared by this method turn these nanocomposites into promising candidates for electronic applications.

Halide Perovskite Crystallization Processes and Methods in Nanocrystals, Single Crystals, and Thin Films

Halide perovskite semiconductors with extraordinary optoelectronic properties have been fascinatedly studied. Halide perovskite nanocrystals, single crystals, and thin films have been prepared for various fields, such as light emission, light detection, and light harvesting. High-performance devices rely on high crystal quality determined by the nucleation and crystal growth process. Here, the fundamental understanding of the crystallization process driven by supersaturation of the solution is discussed and the methods for halide perovskite crystals are summarized. Supersaturation determines the proportion and the average Gibbs free energy changes for surface and volume molecular units involved in the spontaneous aggregation, which could be stable in the solution and induce homogeneous nucleation only when the solution exceeds a required minimum critical concentration (C_min ). Crystal growth and heterogeneous nucleation are thermodynamically easier than homogeneous nucleation due to the existent surfaces. Nanocrystals are mainly prepared via the nucleation-dominated process by rapidly increasing the concentration over C_min , single crystals are mainly prepared via the growth-dominated process by keeping the concentration between solubility and C_min , while thin films are mainly prepared by compromising the nucleation and growth processes to ensure compactness and grain sizes. Typical strategies for preparing these three forms of halide perovskites are also reviewed.

Preparation of ultra-stable and environmentally friendly CsPbBr3@ZrO2/PS composite films for white light-emitting diodes

The working stability of perovskite light-emitting diodes (LEDs) has become an urgent bottleneck to be solved in the process of commercialization. Although lead halide perovskite CsPbX₃ (X = Br, I, Cl) quantum dots (QDs) are considered rising stars in the lighting market owing to their excellent optoelectronic properties, they suffer from fluorescence quenching under thermal conditions. Unfortunately, the surfaces of electronic devices inevitably warm up under long-term energization, which is extremely detrimental to the appropriate functioning of CsPbX₃ QDs. Based on the above discussion, the relationship function between the energization time and surface temperature of electronic devices was analyzed, after which a strategy for the preparation of dual-encapsulating perovskites using organic (polystyrene (PS)) and inorganic (ZrO₂) materials was proposed, and the change in optical stability before and after encapsulation was investigated. The results show that the thermal stability of CsPbBr₃@ZrO₂/PS composite films (CFs) after the dual encapsulation was remarkably enhanced, and the assembled white LEDs still retain the initial emission intensity under prolonged high-power operation. In addition, the double encapsulation layer completely suppresses the ion leakage in CsPbBr₃ and avoids damage to the ecosystem. It can be seen that this encapsulation strategy was capable of imparting excellent working stability to the perovskite material, which would clear the obstacles to commercial conversion.

Zero-Dimensional Zn-Based Halides with Ultra-Long Room-Temperature Phosphorescence for Time-Resolved Anti-Counterfeiting

Though fluorescence-tag-based anti-counterfeiting technology has distinguished itself with cost-effective features and huge information loading capacity, the clonable decryption process of spatial-resolved anti-counterfeiting cannot meet the requirements for high-security-level anti-counterfeiting. Herein, we demonstrate a spatial-time-dual-resolved anti-counterfeiting system based on new organic-inorganic hybrid halides BAPPZn₂ (Cl_y Br_1-y )₈ (BAPP=1,4-bis(3-ammoniopropyl)piperazinium, y=0-1) with ultra-long room-temperature phosphorescence (RTP). Remarkably, the afterglow lifetime can be facilely tuned by regulating the halide-induced heavy-atom effect and can be identified by the naked eyes or with the help of a simple machine vision system. Therefore, the short-lived unicolor fluorescence and lasting-time-tunable RTP provide the prerequisites for unicolor-time-resolved anti-counterfeiting, which lowers the decryption-device requirements and further provides the design strategy of advanced portable anti-counterfeiting technology.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Harnessing of Spatially Confined Perovskite Nanocrystals Using Polysaccharide-based Block Copolymer Systems

Metal halide perovskite nanocrystals (PVSK NCs) are generally unstable upon their transfer from colloidal dispersions to thin film devices. This has been a major obstacle limiting their widespread application. In this study, we proposed a new approach to maintain their exceptional optoelectronic properties during this transfer by dispersing brightly emitting cesium lead halide PVSK NCs in polysaccharide-based maltoheptaose-block-polyisoprene-block-maltoheptaose (MH-b-PI-b-MH) triblock copolymer (BCP) matrices. Instantaneous crystallization of ion precursors with favorable coordination to the sugar (maltoheptaose) domains produced ordered NCs with varied nanostructures of controlled domain size (≈10-20 nm). Confining highly ordered and low dimension PVSK NCs in polysaccharide-based BCPs constituted a powerful tool to control the self-assembly of BCPs and PVSK NCs into predictable structures. Consequently, the hybrid thin films exhibited excellent durability to humidity and stretchability with a relatively high PL intensity and photoluminescence quantum yield (>70%). Furthermore, stretchable phototransistor memory devices were produced and maintained with a good memory ratio of 10⁵ and exhibited a long-term memory retention over 10⁴ s at a high strain of 100%.

One-step spray coating strategy toward a highly uniform large-area CsPbBr3@PMMA composite film for backlit display

The large-scale and continuous production of CsPbBr₃@PMMA composite film is realized by the in-situ ultrasonic spray coating method at room temperature. Through embedding CsPbBr₃ nanocrystals into the hydrophobic polymer framework, the as-fabricated films (20 cm × 20 cm) exhibit uniform green emissions with a relatively high PLQYs of 76%, and could maintain 80% PL intensity after 3 months storage under ambient conditions. Assembling the green-emissive CsPbBr₃@PMMA film and the red-emissive KSF@PMMA film with blue LED chip, a high-performance LCD is obtained, reaching a higher saturation with 126% and 94% color gamut of NTSC and Rec.2020, respectively. This work demonstrates that ultrasonic spray coating technique could be widely used in the large-scale fabrication of uniformly high-quality perovskite films for backlight application.

Multifunctional π-Conjugated Additives for Halide Perovskite

Additive is a conventional way to enhance halide perovskite active layer performance in multiaspects. Among them, π-conjugated molecules have significantly special influence on halide perovskite due to the superior electrical conductivity, rigidity property, and good planarity of π-electrons. In particular, π-conjugated additives usually have stronger interaction with halide perovskites. Therefore, they help with higher charge mobility and longer device lifetime compared with alkyl-based molecules. In this review, the detailed effect of conjugated molecules is discussed in the following parts: defect passivation, lattice orientation guidance, crystallization assistance, energy level rearrangement, and stability improvement. Meanwhile, the roles of conjugated ligands played in low-dimensional perovskite devices are summarized. This review gives an in-depth discussion about how conjugated molecules interact with halide perovskites, which may help understand the improved performance mechanism of perovskite device with π-conjugated additives. It is expected that π-conjugated organic additives for halide perovskites can provide unprecedented opportunities for the future improvement of perovskite devices.

Spontaneous Formation of Lead-Free Cs3 Cu2 I5 Quantum Dots in Metal-Organic-Frameworks with Deep-Blue Emission

All-inorganic lead-free Cs₃ Cu₂ I₅  perovskite-derivant quantum dots (QDs) have attracted tremendous attention due to their nontoxicity and unique optoelectronic properties. However, the traditional hot-injection method requires high temperatures and multiple ligands to confine the growth of QDs. Herein, a strategy is reported to spontaneously synthesize ultrasmall Cs₃ Cu₂ I₅  QDs within metal-organic-frameworks (MOFs) MOF-74 at room temperature (RT) with an average diameter of 4.33 nm. The obtained Cs₃ Cu₂ I₅  QDs exhibit an evident deep-blue emission with Commission Internationale de L'Eclairage coordinates of (0.17, 0.07), owing to the strong quantum confinement effect. Due to the protection of MOF-74, the Cs₃ Cu₂ I₅  QDs demonstrate superior stability, and the photoluminescence quantum yield retains 89% of the initial value after the storage of 1440 h under the environment with relative humidity exceeding 70%. Besides, triplet-triplet annihilation upconversion emission is observed within the composite of Cs₃ Cu₂ I₅ @MOF-74, which brings out apparent temperature-dependent photoluminescence. This study reveals a facile method for fabricating ultrasmall lead-free perovskite-derivant QDs at RT without multiple ligands. Besides, the temperature-dependent photoluminescence of Cs₃ Cu₂ I₅ @MOF-74 may open up a new way to develop the applications of temperature sensors or other related optoelectronic devices.

Self-Assembly of CsPbBr3 Perovskites in Micropatterned Polymeric Surfaces: Toward Luminescent Materials with Self-Cleaning Properties

In this work, we present a series of porous, honeycomb-patterned polymer films containing CsPbBr₃ perovskite nanocrystals as light emitters prepared by the breath figure approach. Microscopy analysis of the topography and composition of the material evidence that the CsPbBr₃ nanocrystals are homogeneously distributed within the polymer matrix but preferably confined inside the pores due to the fabrication process. The optical properties of the CsPbBr₃ nanocrystals remain unaltered after the film formation, proving that they are stable inside the polystyrene matrix, which protects them from degradation by environmental factors. Moreover, these surfaces present highly hydrophobic behavior due to their high porosity and defined micropatterning, which is in agreement with the Cassie-Baxter model. This is evidenced by performing a proof-of-concept coating on top of 3D-printed LED lenses, conferring the material with self-cleaning properties, while the CsPbBr₃ nanocrystals embedded inside the polymeric matrix maintain their luminescent behavior.

Encapsulation of Pb-Free CsSnCl3 Perovskite Nanocrystals with Bone Gelatin: Enhanced Stability and Application in Fe3+ Sensing

The toxicity of the Pb element limits the large-scale application of inorganic cesium-lead halide (CsPbX₃, with X = Cl, Br, and I) perovskite nanocrystals (NCs). Pb-free cesium-tin halide (CsSnX₃) NCs have emerged as a viable alternative because of its excellent photoelectric conversion efficiency. However, the applications are hampered by its poor stability and low photoluminescence quantum yield (PLQY). In this study, extraordinarily stable CsSnCl₃ NCs were prepared by exploiting bone gelatin as surface capping agents, which retain 95% of the photoluminescence intensity in water for 55 h. Additionally, after bone gelatin encapsulation, the PLQY of CsSnCl₃ NCs was found to increase from 2.17% to 3.13% for the uncapped counterparts because of an improved radiative recombination rate. With such remarkable optical properties of the bone gelatin-CsSnCl₃ NCs, metal ions like Fe³⁺ in aqueous solutions can be readily detected and monitored, signifying the potential application of such stable bone gelatin-CsSnCl₃ NCs in the development of fluorescence sensors and detectors.

Highly Stable CsSnCl3 Quantum Dots Grown in an Ionic Liquid/Gelatin Composite System through an In Situ Method

Lead halide perovskite quantum dots (QDs) are controversial due to their high lead content. Tin, a low-toxic element with an outer electronic structure similar to that of Pb, becomes a strong candidate for preparing lead-free perovskite QDs. However, tin-based perovskite QDs, especially CsSnCl₃ QDs, exhibit poor environmental stability. Herein, we proposed an strategy for highly stable CsSnCl₃ QDs using an ionic liquid as a solvent and antioxidant and gelatin as a multidentate ligand and coating material through an in situ method ([AMIM]Cl/gelatin-QDs). The results showed that the abundant active groups of gelatin served as the nucleation growth center for QDs and further passivated QDs. At the same time, the long molecular chain of gelatin can coat the QDs to isolate the environment and fully protect QDs, and the size of QDs grown in gelatin was 5-10 nm. In addition, the oxidation resistance of ionic liquids and the halogen-rich environment formed also played an important role. Even if [AMIM]Cl/gelatin-QDs were treated with water and ultraviolet light simultaneously, its remaining fluorescence intensity was still above 60% within 72 h. Meaningfully, QDs endowed the composite system mildew resistance, which can resist the erosion of gelatin by molds, thereby realizing the system's long-term protection toward CsSnCl₃ QDs.

Research Progress in Semiconductor Materials with Application in the Photocatalytic Reduction of CO2

The large-scale burning of non-renewable fossil fuels leads to the gradual increase of the CO2 concentration in the atmosphere, which is associated with negative impacts on the environment. The consequent need to reduce the emission of CO2 resulting from fossil fuel combustion has led to a serious energy crisis. Research reports indicate that the photocatalytic reduction of CO2 is one of the most effective methods to control CO2 pollution. Therefore, the development of novel high-efficiency semiconductor materials has become an important research field. Semiconductor materials need to have a structure with abundant catalytic sites, among other conditions, which is of great significance for the practical application of highly active catalysts for CO2 reduction. This review systematically describes various types of semiconductor materials, as well as adjustments to the physical, chemical and electronic characteristics of semiconductor catalysts to improve the performance of photocatalytic reduction of CO2. The principle of photocatalytic CO2 reduction is also provided in this review. The reaction types and conditions of photocatalytic CO2 reduction are further discussed. We believe that this review will provide a good basis and reference point for future design and development in this field.

Polymerized Hybrid Perovskites with Enhanced Stability, Flexibility, and Lattice Rigidity

The intrinsic soft lattice nature of organometal halide perovskites (OHPs) makes them very tolerant to defects and ideal candidates for solution-processed optoelectronic devices. However, the soft lattice results in low stability towards external stresses such as heating and humidity, high density of phonons and strong electron-phonon coupling (EPC). Here, it is demonstrated that the OHPs with unsaturated 4-vinylbenzylammonium (VBA) as organoammonium cations can be polymerized without damaging the perovskite structure and its tolerance to defects. The polymerized perovskites show enhanced stability and flexibility compared to regular three-dimensional and two-dimensional (2D) perovskites. Furthermore, the polymerized 4-vinylbenzylammonium group improves perovskite lattice rigidity substantially, resulting in a reduced non-radiative recombination rate because of suppressed electron-phonon coupling, and enhanced carrier mobility because of suppressed phonon scattering. 2D polymerized perovskite light-emitting diodes (PeLEDs) with strong electroluminescence at room temperature, and quasi-2D PeLEDs with an external quantum efficiency (EQE) of 23.2% and enhanced operation stability are demonstrated. The work has opened a new way of enhancing the intrinsic stability and optoelectronic properties of OHPs.